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  • 1. Aguiar, Francisca C.
    et al.
    Segurado, Pedro
    Martins, Maria Joao
    Bejarano, Maria Dolores
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Portela, Maria Manuela
    Merritt, David M.
    The abundance and distribution of guilds of riparian woody plants change in response to land use and flow regulation2018In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 55, no 5, p. 2227-2240Article in journal (Refereed)
    Abstract [en]

    1. Many riparian ecosystems in Mediterranean Europe are affected by land use and flow alteration by dams. We focused on understanding how these stressors and their components affect riparian forests in the region. We asked the following questions: (1) Are there well‐defined, responsive riparian guilds? (2) Do dam‐induced streamflows determine abundance and distribution of riparian guilds? (3) What are the main drivers governing composition and cover of riparian guilds in regulated rivers?

    2. We inventoried the cover of riparian woody species in free‐flowing rivers and downstream of dams. We performed a cluster analysis and ordination to derive riparian guilds, using abundance data from 66 riparian woody species and 26 functional plant traits. We used a reduced set of principal components for the environment, land use and hydrology, and general linear modelling to explore the effect of these factors (separately and combined) on riparian guilds.

    3. We found that: (1) four dominant guilds are responsive to disturbance in southwestern European streams, namely the obligate riparian, water‐stress tolerant, deciduous competitive and Mediterranean evergreen guilds; (2) a set of land use and hydrological variables differentially affect the diverse co‐occurring riparian guilds; (3) frequency and duration of high flow pulses and the low‐flow conditions were major drivers of change in landscapes dominated by intensive agriculture and forestry; (4) storage reservoirs reduced the cover of obligate riparian and Mediterranean evergreen guilds, and increased the abundance of water‐stress tolerant and deciduous competitive guilds, while run‐of‐river dams, having limited water storage, reduced both obligate and deciduous competitive guilds.

    4. Synthesis and applications. Future research in southwestern Europe should address the resilience of riparian guilds and the effects of interacting landscape factors and stressors on guild distribution. Streamflow regulations downstream of reservoirs should focus on specific flow components, namely the magnitude of flows, and frequency and duration of extreme flow events. For successful mitigation of the dam‐induced effects on riparian vegetation, river management plans must incorporate the environmental and land use site‐specific contexts.

  • 2.
    Arthington, Angela H
    et al.
    Australian Rivers Institute and eWater Co-operative Research Centre, Griffith University, Brisbane, Qld, Australia.
    Naiman, Robert J
    School of Aquatic & Fishery Sciences, University of Washington-355020, Seattle, WA, U.S.A..
    McClain, Michael E
    UNESCO-IHE Institute for Water Education, Delft, The Netherlands and Department of Earth and Environment, Florida International University, Miami, FL, U.S.A..
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Preserving the biodiversity and ecological services of rivers: new challenges and research opportunities2010In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 55, no 1, p. 1-16Article in journal (Refereed)
    Abstract [en]

    Natural biogeochemical processes and diverse communities of aquatic biota regulate freshwater quantity and quality in ways that are not sufficiently acknowledged nor appreciated by the water resources management community. The establishment and enforcement of environmental flow requirements offer promising means to improve and care for these critical environmental services. This Special Issue provides new insights and novel techniques to determine, protect and restore ecologically and socially sustainable flow regimes, and thereby help achieve the water-related goals of the Millennium Ecosystem Assessment.

    Whilst alteration of flow, sediment, organic matter and thermal regimes interact to reduce biological diversity and the ecological integrity of freshwater ecosystems - and thereby degrade the properties and ecological services most valued by humans - ‘environmental flows' left in rivers, or restored to developed rivers, will sustain many ecological and societal values. The success of river protection and rehabilitation ⁄ restoration depends upon understanding and accurately modelling relationships between hydrological patterns, fluvial disturbance and ecological responses in rivers and floodplains.

    This Special Issue presents new analytical and modelling approaches to support the development of hydro-ecological models and environmental flow standards at multiple spatial scales - applicable to all rivers in any economic and societal setting. Examples include the new framework Ecological Limits of Hydrologic Alteration (ELOHA) founded on hydrological classification and gradient analysis; ecological trait analysis; Bayesian hierarchical modelling; Bayesian Decision Networks; and Integrated Basin Flow Assessment (IBFA).

    Advances in the allocation of flood flows along the River Murray in Australia, an Ecosystems Function Model (HEC-EFM) for the Bill Williams River restoration programme in Arizona (U.S.A), the European Water Framework Directive, and improved management of hydroelectric dams demonstrate the potential for significant ecological recovery following partial restoration of natural river flow regimes.

    Based on contributions to this Special Issue, the action agenda of the 2007 Brisbane Declaration on environmental flows and the wider literature, we propose an invigorated global research programme to construct and calibrate hydro-ecological models and to quantify the ecological goods and services provided by rivers in contrasting hydro-climatic settings across the globe. A major challenge will be to find acceptable ways to manage rivers for multiple uses. Climate change intensifies the urgency. Environmental flows help to preserve the innate resilience of aquatic ecosystems, and thereby offer the promise of improved sustainability and wellbeing for people as well as for ecosystems.

  • 3.
    Bejarano, Maria D.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The effects of hydropeaking on riverine plants: a review2018In: Biological Reviews, ISSN 1464-7931, E-ISSN 1469-185X, Vol. 93, no 1, p. 658-673Article, review/survey (Refereed)
    Abstract [en]

    Hydropeaking refers to frequent, rapid and short-term fluctuations in water flow and water levels downstream and upstream of hydropower stations. Such fluctuations are becoming increasingly common worldwide and are known to have far-reaching effects on riverine vegetation. Novel hydrology caused by hydropeaking has no natural correspondence in freshwater systems, and hence few species have adaptations to all its aspects. Here, we review the literature on hydropeaking effects on riverine plants and define the state of the information on this human alteration of riverine ecosystems. We focus on riparian plants, but also draw on information from aquatic plant species, which exhibit a wide variety of adaptations to inundation and associated processes. Riparian plants face both physiological and physical constraints because of the shifts between submergence and drainage, and erosion of substrates. At the population level, hydropeaking may favour dispersal within, but not between, reservoirs, but may hamper germination, establishment, growth and reproduction. At the community level, strong filtering towards easily dispersed, flexible, flood-tolerant and amphibious plants is expected, although few species share these traits. Hence, most riparian plant species are expected to disappear or be pushed towards the upper boundaries of the regulated river margin. Future research should examine more closely global variation in hydropeaking effects, including other taxonomic groups of species and the diversity of hydropeaking regimes. There is also a need for studies focusing on identifying the boundaries within which hydropeaking could operate without impairing plant life.

  • 4.
    Bejarano, Maria Dolores
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Aguiar, Francisca Constanca
    Riparian plant guilds become simpler and most likely fewer following flow regulation2018In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 55, no 1, p. 365-376Article in journal (Refereed)
    Abstract [en]

    1. River regulation affects riparian systems world-wide and conservation and restoration efforts are essential to retain biodiversity, and the functioning and services of riverine ecosystems. Effects of regulation on plant species richness have been widely addressed, but the filtering effect of regulation on guilds has received less attention.

    2. We used a functional trait approach to identify adaptive plant strategies through regulation-tolerant traits and predict shifts of riparian vegetation communities in response to regulation. We analysed variation in functional diversity across gradients of hydrological alteration in northern Sweden in relation to modified timing and infrequent major floods, along with frequent short-term inundation.

    3. Functional richness was similar in all study sites, but species richness declined with increasing intensity of regulation, and the species lost were largely functionally redundant (i.e. co-existing species that have similar contribution to an ecosystem function). Guilds of species intolerant to waterlogging were particularly unsuccessful in most regulated sites as they were affected by hydropower dams which replace major fluvial disturbances with frequent short inundation events. We predict that this guild will disappear, with likely consequences for the entire riverine ecosystem.

    4. Synthesis and applications. We conclude that functional traits tolerant to waterlogging or submergence and lack of major fluvial disturbances were key to understanding our results. We suggest that the functional trait approach can be integrated with knowledge of other ecosystem components to provide an understanding of ecosystem function that can be used to guide fluvial ecosystem management.

  • 5. Bejarano, Maria Dolores
    et al.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Gonzales del Tanago, Marta
    Marchamalo, Miguel
    Responses of riparian trees and shrubs to flow regulationalong a boreal stream in northern Sweden2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, no 5, p. 853-866Article in journal (Refereed)
    Abstract [en]

    1. Flow dynamics is a major determinant of riparian plant communities. Therefore, flowregulation may heavily affect riparian ecosystems. Despite the large number of damsworldwide, little specific information is available on the longitudinal impacts of dams onvegetation, for example how far downstream and at what degree of regulation a dam on ariver can influence riparian woodlands.

    2. We quantified the long-term responses of riparian trees and shrubs to flow regulation byidentifying their lateral distribution and habitat conditions along a boreal river in northernSweden that has been regulated by a single dam since 1948. The regulation has reducedannual flow fluctuations, this effect being largest at the dam, downstream from which itprogressively decreases following the entrance of free-flowing tributaries.

    3. We related changes in the distribution patterns, composition, abundance and richness oftree and shrub species to the degree of regulation along the river downstream from thedam. Regulation has triggered establishment of trees and shrubs closer to the channel,making it possible to measure ecological impacts of flow regulation as differences invegetation attributes relative to the positions of tree and shrub communities establishedbefore and after regulation.

    4. Trees and shrubs had migrated towards the mid-channel along the entire study reach,but the changes were largest immediately downstream of the dam. Shrubs were mostimpacted by flow regulation in terms of lateral movement, but the effect on trees extendedfurthest downstream.

    5. The species composition of trees progressively returned to its pre-regulation state withdistance downstream, but entrance of free-flowing tributaries and variation in channelmorphology and substratum caused local deviations. Species richness after regulationincreased for trees but decreased for shrubs. The changes in species composition andrichness of trees and shrubs showed no clear downstream patterns, suggesting that otherfactors than the degree of regulation were more important in governing life form.

  • 6.
    Bejarano, Maria Dolores
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sordo-Ward, Alvaro
    Alonso, Carlos
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Characterizing effects of hydropower plants on sub-daily flow regimes2017In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 550, p. 186-200Article in journal (Refereed)
    Abstract [en]

    A characterization of short-term changes in river flow is essential for understanding the ecological effects of hydropower plants, which operate by turning the turbines on or off to generate electricity following variations in the market demand (i.e., hydropeaking). The goal of our study was to develop an approach for characterizing the effects of hydropower plant operations on within-day flow regimes across multiple dams and rivers. For this aim we first defined ecologically meaningful metrics that provide a full representation of the flow regime at short time scales from free-flowing rivers and rivers exposed to hydropeaking. We then defined metrics that enable quantification of the deviation of the altered short-term flow regime variables from those of the unaltered state. The approach was successfully tested in two rivers in northern Sweden, one free-flowing and another regulated by cascades of hydropower plants, which were additionally classified based on their impact on short-term flows in sites of similar management. The largest differences between study sites corresponded to metrics describing sub-daily flow magnitudes such as amplitude (i.e., difference between the highest and the lowest hourly flows) and rates (i.e., rise and fall rates of hourly flows). They were closely followed by frequency-related metrics accounting for the numbers of within-day hourly flow patterns (i.e., rises, falls and periods of stability of hourly flows). In comparison, between-site differences for the duration-related metrics were smallest. In general, hydropeaking resulted in higher within-day flow amplitudes and rates and more but shorter periods of a similar hourly flow patterns per day. The impacted flow feature and the characteristics of the impact (i.e., intensity and whether the impact increases or decreases whatever is being described by the metric) varied with season. Our approach is useful for catchment management planning, defining environmental flow targets, prioritizing river restoration or dam reoperation efforts and contributing information for relicensing hydropower dams. 

  • 7. Bell, David
    et al.
    Hjältén, Joakim
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jørgensen, Dolly
    Johansson, Therese
    Forest restoration to attract a putative umbrella species, the white-backed woodpecker, benefited saproxylic beetles2015In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 6, no 12, article id 278Article in journal (Refereed)
    Abstract [en]

    Umbrella species are often spatially demanding and have limited ability to adapt to environmental changes induced by human land-use. This makes them vulnerable to human encroachment. In Sweden, broadleaved trees are disadvantaged by forestry, and commercially managed forests are often deprived of dead wood. This has led to a situation where previously widespread top predators in saproxylic food webs, such as the white-backed woodpecker (Dendrocopos leucotos), have become species of conservation concern. The white-backed woodpecker is generally considered an umbrella species, and it has been linked to forests with large volumes of dead wood from broadleaved trees. In recent years, forest stands have been restored for the white-backed woodpecker, but post-treatment evaluations have rarely included other species that also occur in broad-leaved forests (co-occurring species). Many co-occurring species are saproxylic beetles. In this study, we collected saproxylic beetles and environmental data in restored and commercially managed forests to evaluate if habitat restoration for the white-backed woodpecker also benefited other species with similar habitat associations. We found that volumes of coarse woody debris were higher in restored than in commercially managed forests, and that a majority of man-made snags and downed logs were created from birch trees (Betula spp.). Most spruce trees (Picea abies) were extracted during forest restoration, and this opened up the forest canopy, and created stands dominated by broadleaved trees. Many saproxylic beetles were more common in restored forests, and there were significant differences in species composition between treatments. These differences were largely explained by species traits. Effects of sun-exposure were particularly important, but many beneficiary species were also linked to dead wood from broadleaved trees. Red-listed saproxylic beetles showed a similar pattern with more species and individuals in restored sites. The white-backed woodpecker is still critically endangered in Sweden, but important prey species are already responding to forest restoration at the stand level. We recognize that landscape-level improvements will be required to bring the white-backed woodpecker back, but also that the umbrella species concept can provide a useful framework for successful forest restoration as many co-occurring saproxylic beetle species seemingly benefitted from restoration for the white-backed woodpecker.

  • 8. Bruno, Daniel
    et al.
    Gutierrez-Canovas, Cayetano
    Sanchez-Fernandez, David
    Velasco, Josefa
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Impacts of environmental filters on functional redundancy in riparian vegetation2016In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 53, no 3, p. 846-855Article in journal (Refereed)
    Abstract [en]

    1. Understanding and predicting ecosystem responses to multiple environmental pressures is a long-standing interest in ecology and environmental management. However, few studies have examined how the functional features of freshwater biological communities vary along multiple gradients of environmental stress. Furthermore, modelling these functional features for a whole river network constitutes a strong potential basis to improve ecosystem management. 2. We explored how functional redundancy of biological communities (FR, a functional feature related to the stability, resistance and resilience of ecosystems) responds to single and multiple environmental filters. We compared these responses with those of functional richness, evenness and divergence. We used riparian vegetation of a Mediterranean basin, and three of the main environmental filters affecting freshwater communities in such regions, that is drought, flow regulation and agricultural intensity, thus considering the potential effect of natural environmental variability. We also assessed the predictability of FR and estimated it for the entire river network. 3. We found that all functional measures decreased with increasing environmental filter intensity. However, FR was more sensitive to single and multiple environmental filters compared to other functional measures. The best-fitting model explained 59% of the FR variability and included agriculture, drought and flow regulation and the pairwise interactions of agriculture with drought and flow regulation. The parameters of the FR models differed from null model expectations reflecting a non-random decline along stress gradients. 4. Synthesis and applications. We found non-random detrimental effects along environmental filters' gradients for riparian functional redundancy (the most sensitive functional index), meaning that increased stress could jeopardize stability, resistance and resilience of these systems. In general, agriculture caused the greatest impact on functional redundancy and functional diversity measures, being the most important stressor for riparian functionality in the study area. Temporary streams flowing through an agricultural, regulated basin had reduced values of functional redundancy, whereas the free-flowing medium-sized, perennial water courses flowing through unaltered sub-basins displayed higher values of functional redundancy and potentially greater stability against human impacts. All these findings along with the predicted basin-wide variation of functional redundancy can assist environmental managers in improving monitoring and ecosystem management.

  • 9. Bång, Åsa
    et al.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Holm, Svante
    The potential role of tributaries as seed sources to an impoundment in northern Sweden: a field experiment with seed mimics2007In: Rivers Research and Applications: an international journal devoted to river research and management, ISSN 1535-1459, E-ISSN 1535-1467, Vol. 23, p. 1049-1057Article in journal (Refereed)
  • 10.
    Catford, Jane A.
    et al.
    Department of Resource Management and Geography, The University of Melbourne, Australia.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reducing redundancy in invasion ecology by integrating hypotheses into a single theoretical framework2009In: Diversity & distributions: A journal of biological invasions and biodiversity, ISSN 1366-9516, E-ISSN 1472-4642, Vol. 15, no 1, p. 22-40Article in journal (Refereed)
    Abstract [en]

    Aim: Invasion ecology includes many hypotheses. Empirical evidence suggests that most of these can explain the success of some invaders to some degree in some circumstances. If they all are correct, what does this tell us about invasion? We illustrate the major themes in invasion ecology, and provide an overarching framework that helps organize research and foster links among subfields of invasion ecology and ecology more generally.

    Location: Global.

    Methods: We review and synthesize 29 leading hypotheses in plant invasion ecology. Structured around propagule pressure (P), abiotic characteristics (A) and biotic characteristics (B), with the additional influence of humans (H) on P, A and B (hereon PAB), we show how these hypotheses fit into one paradigm. P is based on the size and frequency of introductions, A incorporates ecosystem invasibility based on physical conditions, and B includes the characteristics of invading species (invasiveness), the recipient community and their interactions. Having justified the PAB framework, we propose a way in which invasion research could progress.

    Results: By highlighting the common ground among hypotheses, we show that invasion ecology is encumbered by theoretical redundancy that can be removed through integration. Using both holistic and incremental approaches, we show how the PAB framework can guide research and quantify the relative importance of different invasion mechanisms.

    Main conclusions: If the prime aim is to identify the main cause of invasion success, we contend that a top-down approach that focuses on PAB maximizes research efficiency. This approach identifies the most influential factors first, and subsequently narrows the number of potential causal mechanisms. By viewing invasion as a multifaceted process that can be partitioned into major drivers and broken down into a series of sequential steps, invasion theory can be rigorously tested, understanding improved and effective weed management techniques identified.

  • 11. Chapin, F Stuart
    et al.
    Hoel, Michael
    Carpenter, Steven R
    Lubchenco, Jane
    Walker, Brian
    Callaghan, Terry V
    Folke, Carl
    Levin, Simon A
    Mäler, Karl-Göran
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Barrett, Scott
    Berkes, Fikret
    Crépin, Anne-Sophie
    Danell, Kjell
    Rosswall, Thomas
    Starrett, David
    Xepapadeas, Anastasios
    Zimov, Sergey A
    Building resilience and adaptation to manage Arctic change2006In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 35, no 4, p. 198-202Article in journal (Refereed)
  • 12. Dahlström, N
    et al.
    Jönsson, K
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Long term dynamics of large woody debris in a managed boreal forest stream2005In: Forest Ecology and Management, ISSN 0378-1127, E-ISSN 1872-7042, Vol. 210, no 1-3, p. 363-373Article in journal (Refereed)
    Abstract [en]

    Little is known about how past forest management in Sweden influenced the quantity and quality of large woody debris (LWD) in streams. The present study provides information of the long-term dynamics of LWD in a reach of a boreal stream intersecting a managed forest. Dendrochronological methods were used to reconstruct mortality years of the pieces of LWD and the general history of fire and cuttings of the surrounding riparian forest. Today, spruce dominates among the living trees, whereas the LWD is dominated by birch in the forest and by pine in the stream. Fire frequency prior to active fire suppression was similar to values reported from boreal forests. Pine trees were more abundant in the riparian forest before selective logging operations and active fire suppression began in the 1800s. Many of the pieces of LWD found in the stream today died more than 200 years ago and derived from a cohort of pines that generated in the early 1600s. Pine LWD in stream channels is highly resistant to decomposition and can reside for more than 300 years. A substantial amount of the LWD found today in managed forest streams in boreal Sweden most likely derives from the time before extensive human influence and is likely to decrease further in the future. Management of riparian forests to ascertain future supply of long-lived LWD in streams should target to increase the proportion of pine trees.

  • 13. Dahlström, N
    et al.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The dynamics of coarse woody debris in boreal Swedish forests are similar between stream channels and adjacent riparian forests2006In: Canadian Journal of Forest Research, ISSN 0045-5067, E-ISSN 1208-6037, Vol. 36, no 5, p. 1139-1148Article in journal (Refereed)
  • 14.
    Dahlström, Niklas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Influence of woody debris on channel structure in old growth and managedforest streams in central Sweden2004In: Environmental Management, ISSN 0364-152X, E-ISSN 1432-1009, Vol. 33, no 3, p. 376-384Article in journal (Refereed)
    Abstract [en]

    Anecdotal information suggests that woody debris have had an important channel-forming role in Swedish streams and rivers, but there are few data to support this view. We identified 10 streams within near-natural and 10 streams within managed forest landscapes in central Sweden, and quantified their channel characteristics and content of woody debris. All pieces of woody debris greater than 0.5 m in length and greater than 0.05 m in base diameter were included. The near-natural forests were situated in reserves protected from forest cutting, whereas the managed forests had previously faced intensive logging in the area adjacent to the stream, The two sets of streams did not differ in general abiotic characteristics such as width, slope, or boulder cover, but the number of wood pieces was twice as high and the wood volume almost four times as high in the near-natural streams. This difference resulted in a higher frequency of debris dams in the near-natural streams. Although the total pool area did not differ between the two sets of streams, the wood-formed pools were larger and deeper, and potentially ecologically more important than other pools. In contrast to what has been believed so far, woody debris can be a channel-forming agent also in steeper streams with boulder beds. In a step-wise multiple regression analysis, pool area was positively and most strongly related to the quantity of woody debris, whereas channel gradient and wood volume were negatively related. The frequency of debris dams increased with the number of pieces of woody debris, but was not affected by other variables. The management implications of this study are that the wood quantity in streams in managed forests would need to be increased if management of streams will target more pristine conditions.

  • 15. De Frenne, Pieter
    et al.
    Brunet, Jörg
    Shevtsova, Anna
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    Kolb, Annette
    Graae, Bente J
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Chabrerie, Olivier
    Cousins, Sara AO
    Decocq, Guillaume
    De Schrijver, An
    Diekmann, Martin
    Gruwez, Robert
    Heinken, Thilo
    Hermy, Martin
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stanton, Sharon
    Tack, Wesley
    Willaert, Justin
    Verheyen, Kris
    Temperature effects on forest herbs assessed by warmingand transplant experiments along a latitudinal gradient2011In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 17, no 10, p. 3240-3253Article in journal (Refereed)
    Abstract [en]

    Slow-colonizing forest understorey plants are probably not able to rapidly adjust their distribution range following large-scale climate change. Therefore, the acclimation potential to climate change within their actual occupied habitats will likely be key for their short- and long-term persistence. We combined transplant experiments along a latitudinal gradient with open-top chambers to assess the effects of temperature on phenology, growth and reproductive performance of multiple populations of slow-colonizing understorey plants, using the spring flowering geophytic forb Anemone nemorosa and the early summer flowering grass Milium effusum as study species. In both species, emergence time and start of flowering clearly advanced with increasing temperatures. Vegetative growth (plant height, aboveground biomass) and reproductive success (seed mass, seed germination and germinable seed output) of A. nemorosa benefited from higher temperatures. Climate warming may thus increase future competitive ability and colonization rates of this species. Apart from the effects on phenology, growth and reproductive performance of M. effusum generally decreased when transplanted southwards (e.g., plant size and number of individuals decreased towards the south) and was probably more limited by light availability in the south. Specific leaf area of both species increased when transplanted southwards, but decreased with open-top chamber installation in A. nemorosa. In general, individuals of both species transplanted at the home site performed best, suggesting local adaptation. We conclude that contrasting understorey plants may display divergent plasticity in response to changing temperatures which may alter future understorey community dynamics.

  • 16. De Frenne, Pieter
    et al.
    Graae, Bente J
    Department of Biology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Brunet, Joerg
    Shevtsova, Anna
    Umeå University, Faculty of Medicine, Department of Medical Biochemistry and Biophysics.
    De Schrijver, An
    Chabrerie, Olivier
    Cousins, Sara AO
    Decocq, Guillaume
    Diekmann, Martin
    Hermy, Martin
    Heinken, Thilo
    Kolb, Annette
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Stanton, Sharon
    Verheyen, Kris
    The response of forest plant regeneration to temperature variation along a latitudinal gradient2012In: Annals of Botany, ISSN 0305-7364, E-ISSN 1095-8290, Vol. 109, no 5, p. 1037-1046Article in journal (Refereed)
    Abstract [en]

    The response of forest herb regeneration from seed to temperature variations across latitudes was experimentally assessed in order to forecast the likely response of understorey community dynamics to climate warming. Seeds of two characteristic forest plants (Anemone nemorosa and Milium effusum) were collected in natural populations along a latitudinal gradient from northern France to northern Sweden and exposed to three temperature regimes in growth chambers (first experiment). To test the importance of local adaptation, reciprocal transplants were also made of adult individuals that originated from the same populations in three common gardens located in southern, central and northern sites along the same gradient, and the resulting seeds were germinated (second experiment). Seedling establishment was quantified by measuring the timing and percentage of seedling emergence, and seedling biomass in both experiments. Spring warming increased emergence rates and seedling growth in the early-flowering forb A. nemorosa. Seedlings of the summer-flowering grass M. effusum originating from northern populations responded more strongly in terms of biomass growth to temperature than southern populations. The above-ground biomass of the seedlings of both species decreased with increasing latitude of origin, irrespective of whether seeds were collected from natural populations or from the common gardens. The emergence percentage decreased with increasing home-away distance in seeds from the transplant experiment, suggesting that the maternal plants were locally adapted. Decreasing seedling emergence and growth were found from the centre to the northern edge of the distribution range for both species. Stronger responses to temperature variation in seedling growth of the grass M. effusum in the north may offer a way to cope with environmental change. The results further suggest that climate warming might differentially affect seedling establishment of understorey plants across their distribution range and thus alter future understorey plant dynamics.

  • 17.
    Dietrich, Anna L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A phytometer study evaluating the effects of stream restoration on riparian vegetation2016In: Ecohydrology, ISSN 1936-0584, E-ISSN 1936-0592, Vol. 9, no 4, p. 646-658Article in journal (Refereed)
    Abstract [en]

    Channelization of streams and rivers to facilitate timber floating has cut off riparian zones from the channel, covered them with coarse sediment and resulted in less flooding. Restoration measures aiming to counteract these impacts are expected to create a higher, more natural hydrological variability and enhance site quality for riparian plants. In a long-term field experiment, we evaluated the effect of flooding regime on riparian plant performance by measuring survival and biomass increment of two transplanted phytometer species, a grass (Molinia caerulea) and a forb (Filipendula ulmaria). We also analysed the number and duration of flooding events in channelized and restored stream and river reaches with an indirect method using diurnal temperature oscillation. We found that flow duration was higher, with significantly more flood events at restored compared with channelized sites in medium-sized and large watercourses, particularly during the summer months. Phytometer performance was better at restored sites, and it was positively correlated with duration and frequency of summer flooding, indicating that more but less intense floods after restoration improved site conditions for phytometer growth. This may not only result from an increased heterogeneity in channel morphology caused by the return of boulders but can probably also be attributed to a reduced current velocity at restored sites. Flood variables were more often correlated with other abiotic variables at restored than at channelized sites, which points to an increased land-water connectivity as a result of restoration. 

  • 18.
    Dietrich, Anna L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Restoration effects on germination and survival of plants in the riparian zone: a phytometer study2015In: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 216, no 3, p. 465-477Article in journal (Refereed)
    Abstract [en]

    Many streams that were channelized to facilitate timber floating in northern Sweden, have in recent years been restored by returning coarse sediment (cobbles and boulders) to the channel and reconnecting riparian with instream habitats. We asked if such restoration measures affect germination and survival of plants in the riparian zone, and if such potential effects depend on location in the catchment. We used a paired site approach, comparing the performance of Helianthus annuus (sunflower) phytometers (seeds and seedlings) in the riparian zone in channelized versus restored river reaches along climate and stream size gradients in the Vindel River catchment in northern Sweden. Phytometer survival, substrate availability, and soil nutrient content in large streams were enhanced by restoration, but overall, phytometer performance was negatively related to the length of the growing season, i.e. phytometers grew best at high altitudes and short growing seasons. This result may have been caused by less competition from the shorter and sparser neighbouring vegetation at these sites or to more frequent flooding events, enhancing retention of organic matter. Soil nutrient levels were lowest close to the coast and in large streams, probably due to deposition of mineral sediment. The higher availability of riparian habitat at restored than at channelized sites suggests that plant species richness and abundance may potentially increase after restoration. Seedling transplantation seems to be a preferable revegetation measure, because phytometer seedlings established better than seeds and survival was significantly higher at restored sites. The good plant performance at sites with short growing seasons and high altitudes suggests that, with limited resources, restoration measures should first be located to such sites.

  • 19.
    Dietrich, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lind, Lovisa
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The Use of Phytometers for Evaluating Restoration Effects on Riparian Soil Fertility2014In: Journal of Environmental Quality, ISSN 0047-2425, E-ISSN 1537-2537, Vol. 43, no 6, p. 1916-1925Article in journal (Refereed)
    Abstract [en]

    The ecological restoration of streams in Sweden has become increasingly important to counteract effects of past timber floating. In this study, we focused on the effect on riparian soil properties after returning coarse sediment (cobbles and boulders) to the channel and reconnecting riparian with instream habitats. Restoration increases habitat availability for riparian plants, but its effects on soil quality are unknown. We also analyzed whether the restoration effect differs with variation in climate and stream size. We used standardized plant species to measure the performance of a grass (Phleum pratense L.) and a forb (Centaurea cyanus L.) in soils sampled in the riparian zones of channelized and restored streams and rivers. Furthermore, we analyzed the mass fractions of carbon (C) and nitrogen (N) along with the proportions of the stable isotopes C-13 and N-15 in the soil, as well as its grain size composition. We found a positive effect of restoration on biomass of phytometers grown in riparian soils from small streams, indicating that restoration enhanced the soil properties favoring plant performance. We suggest that changed flooding with more frequent but less severe floods and slower flows, enhancing retention, could explain the observed patterns. This positive effect suggests that it may be advantageous to initiate restoration efforts in small streams, which make up the highest proportion of the stream network in a catchment. Restoration responses in headwater streams may then be transmitted downstream to facilitate recovery of restored larger rivers. If the larger rivers were restored first, a slower reaction would be expected.

  • 20.
    Dietrich, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    A long-term phytometer study to evaluate stream restoration along climate and discharge gradientsManuscript (preprint) (Other academic)
    Abstract [en]

    Simplified channel morphology caused by the channelization of rivers to facilitatetimber floating resulted in a less variable flow regime with faster flows in the mainchannel. Restoration measures aiming to counteract these impacts, such as the returnof boulders to the channel and the reconnection of the riparian zone with instreamhabitats, are expected to create a higher, more natural hydrological variability andenhance riparian site quality. In this study, we analysed the number and duration offlooding events at channelized and restored river reaches with an indirect methodusing diurnal temperature oscillation. In a long-term field experiment, we evaluatedthe effect of flooding regime on riparian plant performance by measuring survival andbiomass increment of two transplanted phytometer species, a grass (Molinia caerulea)and a forb (Filipendula ulmaria). We found that flow variability was significantlyhigher at restored compared to channelized sites in medium-sized and large streams,particularly during summer months. Phytometer performance was better at restoredsites and positively correlated with summer flooding, indicating that a more variableflow after restoration improved site conditions for phytometer growth. This may notonly result from the higher heterogeneity in channel morphology caused by thereturned boulders, but can probably also be attributed to a lower flow velocity atrestored sites. Flood variables were more often correlated with other abiotic variablesat restored than at channelized sites, which points to an increased land-waterconnectivity as a result of restoration.

  • 21.
    Dietrich, Anna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Phytometers are underutilised for evaluating ecological restoration2013In: Basic and Applied Ecology, ISSN 1439-1791, E-ISSN 1618-0089, Vol. 14, no 5, p. 369-377Article in journal (Refereed)
    Abstract [en]

    Ecological restoration increases, but evaluation of restoration efforts is inadequate because reliable performance indicators are lacking. As plants are important actors in ecological restoration, we suggest that they be used as meters, i.e. phytometers, of restoration success. Phytometer plants are transplanted to different conditions to integrate measures of the prevailing conditions. We analysed 100 studies for the use of phytometers and especially their applicability to evaluate ecological restoration. Most studies employed single species and life-stages and focused on habitat conditions and environmental impacts. Most experiments were conducted on grasslands in wet temperate regions. Growth was the dominant response variable, in long-term studies often combined with reproductive output and plant survival. Only five studies specifically evaluated ecological restoration, implying that its potential is not yet realised. We found phytometers promising in evaluating restoration outcomes given that they are easy to measure, can provide rapid results, and serve as integrative indicators of environmental conditions with the ability of covering many aspects of plant life and ecosystem processes. To evaluate restoration success with high resolution and generality, we suggest a combination of different phytometer species, life-forms and life-stages, and experimental periods >1 year to reduce effects of transplantation and between-year variation and to account for time lags in ecological processes and changes after restoration.

  • 22. Dunn, RM
    et al.
    Colwell, RK
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The river domain: why are there more species halfway up the river?2006In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 29, no 2, p. 251-259Article in journal (Refereed)
  • 23.
    Dynesius, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Stockholms universitet, Botaniska institutionen.
    Hylander, Kristoffer
    Stockholms universitet, Botaniska institutionen.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    High resilience of bryophyte assemblages in streamside compared to upland forests2009In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 90, no 4, p. 1042-1054Article in journal (Refereed)
    Abstract [en]

    Landscape heterogeneity causes spatial variation in disturbance regimes and resilience. We asked whether the resilience of bryophyte (liverwort and moss) assemblages to clear-cutting differs between streamside and upland boreal forests in northern Sweden. We hypothesized that bryophyte survival and recolonization rates are higher in streamside areas, thus raising resilience. Conversely, disturbance-intolerant but also invading species should be more frequent here, potentially reducing resilience. In each of 18 sites, we compared two 0.1-ha plots (one streamside and one upland) located in old forest that had never been clear-cut with two matching plots in young stands established after clear-cutting of old forests 30-50 years earlier. We used the magnitude of the difference in assemblages between old and young stands as a measure of change and, therefore, resilience (large difference implying low resilience). Species assemblages were more resilient in streamside than in upland forests. Species composition changed significantly in upland but not in streamside forests. Reductions in species richness were more pronounced in upland forests for total richness and for eight subgroups of species. Two results indicated lower survival/recolonization in upland forests: (1) species had a stronger association with old stands in upland areas, and (2) among species present in both the old streamside and old upland plot in a site, fewer appeared in the young upland than in the corresponding streamside plot. Simultaneously, a higher proportion of species invaded streamside areas; 40 of the 262 species encountered in streamside forests increased their occupancy by two or more sites compared to only two of 134 species in uplands. We suggest that in boreal forests spatial variation in resilience of assemblages of forest organisms intolerant of canopy removal is related to factors governed mainly by topography. More generally, we argue that landscape-scale variation in resilience of assemblages is influenced by spatial variation in (1) stress and resource availability, (2) number of  disturbance intolerant species, and (3) magnitude of environmental changes brought about by a disturbance with a specific intensity. We also suggest that rapid recovery in the short term does not necessarily imply higher long-term ability to return to the pre-disturbance state.

  • 24.
    Dynesius, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Johansson, Mats E
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Intercontinental similarities in riparian-plant diversity and sensitivity to river regulation2004In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 14, p. 173-191Article in journal (Refereed)
    Abstract [en]

    We asked whether assemblages of species with separate evolutionary histories differed in their response to similar human interventions. We assessed this by comparing the response of riparian plant communities to river regulation on two different continents. We compared free-flowing and regulated rivers between boreal parts of North America (Alberta and British Columbia) and Europe (Sweden), using a standardized sampling protocol and the same field staff on both continents. Although the two regions shared few species, both riparian plant-species diversity along free-flowing rivers and the response to different kinds of flow regulation were similar between the continents. The number of riparian-plant species and their amount of cover differed among types of water-level regime, but the continental affiliation of a river-margin site did not statistically explain any of the variation. Within continents, the local flora of the regulated river-margin sites was largely similar in species composition to the free-flowing ones, but the sites along storage reservoirs were more species-poor. The similarity in the response to regulation between the continents suggests that general guidelines for rehabilitation of degraded boreal rivers are a realistic goal. The number of species and genera, plant cover, and species numbers in most trait groups (classified according to growth form and life span) were similar between free-flowing river margins in Europe and North America. Moreover, the regional native species pools of northern Sweden and Alberta were similar in size and composition of species groups, despite the fact that only 27% of the species in Alberta were found in northern Sweden. This is presumably because the floras share a common Tertiary origin and because the regions have had largely similar late-Tertiary and Quaternary histories. The most pronounced difference between the continents was that we found no exotic species on the 183 Swedish river-margin sites, whereas 9% of the species found in all 24 North American plots taken together were exotics. All North American exotics found have occurred in Europe since prehistoric times, and the difference in exotic richness most likely reflects a difference in the number of species humans have transferred from one continent to another, rather than a difference in invasibility between the regions.

  • 25.
    Dynesius, Mats
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Åström, Marcus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Microclimatic buffering by logging residues and forest edges reduces clear-cutting impacts on forest bryophytes2008In: Applied Vegetation Science, ISSN 1402-2001, E-ISSN 1654-109X, Vol. 11, no 3, p. 345-354Article in journal (Refereed)
    Abstract [en]

    Question: The practice of extracting logging residues after clear-cutting for bioenergy purposes is spreading. Logging residues constitute a shelter in clear-cut areas and therefore concerns have been expressed that their removal could make the ground and its vegetation more exposed to extreme micro¬climatic conditions. We asked whether logging residues and forest edges can protect ground-dwelling forest bryophytes from fatal microclimate events following clear-cutting.

    Location: Boreal forests of central Sweden.

    Methods: Using transplants of eight forest floor bryophyte species we experimentally analysed the sheltering effect (less solar radiation and less wind) of logging residues and forest edges in seven clear-cut areas. Transplants were placed in two contrasting positions in each area; near a north-facing forest edge and in the centre of the clear-cut area. In each position, half of the transplants were covered by a layer of spruce branches and the other half was left uncovered. We estimated proportion of apparently living shoots (apparent vitality) and measured radial growth of transplants during one growing season.

    Results: Position in the clear-cut area, but not cover of spruce branches, clearly influenced radial growth. Vitality scores were higher among transplants covered with branches and the lowest apparent vitality was observed in uncovered transplants in the middle of clear-cut areas. The change in area of apparently liv¬ing shoots during the course of the experiment (growth minus mortality) was unaffected by branch cover close to the edge but positively affected in the centre of the clear-cut area. In general, the effect of branch cover on bryophytes was higher in the centre of clear-cut areas. Here, climatic measurements showed that branch cover buffers during periods of extreme microclimates.

    Conclusions: Extraction of logging residues after clear-felling may reduce the survival of some ground-dwelling forest organisms. The additional sheltering provided by branches was unimportant close to forest edges. We suggest smaller clear-cut areas, green-tree retention and other ways to make logged areas shadier and less windy to mitigate the reduced shelter caused by harvest of logging residues.

  • 26.
    Engström, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Helfield, James
    Department of Environmental Science, Huxley College of the Environment, Western Washington University, Bellingham, Washington 98225-9181 USA.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palm, Daniel
    Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Science SE-901 83 Umeå, Sweden.
    Large wood restoration in boulder dominated streamsArticle in journal (Other academic)
    Abstract [en]

    1. An important aim of many restoration activities is to improve ecological structures and processes that have a central role for ecosystem functioning.  Large wood (LW) is such a component, affecting hydraulics, channel morphology, floodplain dynamics, and ecological communities.

    2. We studied the effect of in-stream wood restoration, evaluating the difference before and after wood addition using boulder restored sites as controls. We investigated channel dynamics, movement and recruitment of large wood, retention of propagules and fish communities.

    3. One of three streams experienced a reduced current velocity after LW placement. The width of the channel and the reduced velocity were probably the reasons why this stream trapped most naturally drifting wood. LW sites experienced increased retention of organic matter compared to control sites, but LW proved to be unimportant in controlling brown trout density and biomass.

    4. Restoring habitat heterogeneity has been widely used to enhance ecological functioning, but during the last years its potential to restore streams and rivers has been questioned. In streams affected by multiple stressors, increased habitat heterogeneity is less important. Our result demonstrates that restoration with wood can enhance the restoration made with only boulders, and as a consequence advance ecological functioning.

  • 27.
    Engström, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Weber, Christine
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of river ice on riparian vegetation2011In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 56, no 6, p. 1095-1105Article in journal (Refereed)
    Abstract [en]

    1.  Many rivers and streams experience pronounced ice dynamics caused by the formation of anchor and frazil ice, leading to flooding and disturbance of riparian and aquatic communities.  The effects of dynamic ice conditions on riverine biota are little known.

    2.  We studied the formation of anchor ice in natural streams over 2 years, and assessed the effects of anchor ice on riparian vegetation by comparing sites with frequent or abundant and little or no anchor ice formation. We also studied the direct impact of ice on riparian plants by experimentally creating ice in the riparian zone over three winters, and by exposing plants of different life-forms to ‑18oC cold ice in the laboratory.

    3.  Riparian species richness per 1-m2 plot was higher at sites affected by anchor ice than at sites where anchor ice was absent or rare. Dominance was lower at anchor ice sites, suggesting that ice disturbance enhanced species richness. Species composition was more homogenous among plots at anchor ice sites. Experimentally creating riparian ice corroborated the comparative results, with species richness increasing in ice-treated plots compared to controls, irrespective of whether the sites showed natural anchor ice.

    4.  Because of human alterations of running waters, the natural effects of river ice on stream hydrology, geomorphology and ecology are little known.  Global warming in northern streams will lead to more dynamic ice conditions, offering new challenges for aquatic organisms and river management.  We expect that the results discussed here can stimulate new research, contributing to a better understanding of ecosystem function during winter.

  • 28.
    Engström, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of stream restoration on dispersal of plant propagules2009In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 46, no 2, p. 397-405Article in journal (Refereed)
    Abstract [en]

    1. Species immigration is vital for the success of restoring degraded ecosystems, but the effectiveness of enhancing dispersal following restoration is seldom evaluated. Running water is an important vector for plant dispersal. Frequency and duration of floods and channel-network complexity are important factors influencing propagule dispersal. In Sweden, these functions have been modified by channelization to facilitate timber floating, thus hampering emigration and immigration of riparian propagules.

    2. During the last 10–20 years, affected watercourses have been restored by removing barriers and replacing boulders into channels. This is hypothesized to facilitate retention of water-dispersed propagules. We studied the efficiency of propagule retention following restoration by releasing propagule mimics and by placing propagule traps in the riparian zone.

    3. Retention of propagule mimics was highest in sites restored with boulders and large wood. Retention occurred at both high and low flows but was most efficient during low flows when mimics were trapped by boulders and wood. Waterborne propagules ending up at such sites are unlikely to establish unless they can reach the riparian zone later. At high flows, floating propagules are more likely to reach riparian areas suitable for establishment. According to propagule traps placed at various levels of the riparian zone, deposition of plant propagules and sediments did not increase in restored sites.

    4. Synthesis and applications. Our study not only demonstrates that restoration of channel complexity through replacement of boulders and wood can enhance retention of plant propagules, but also it highlights the importance of understanding how restoration effects vary with flow. Most streams are restored to function optimally during median or average flows, whereas communities often are controlled by ecological processes acting during extreme flow events. We advocate that stream restoration should be designed for optimal function during those discharges under which the ecological processes in question are most important, which in this case is, during high flow.

  • 29.
    Gardeström, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Holmqvist, Daniel
    Vindel River Fishery Advisory Board.
    Polvi, Lina E.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Demonstration Restoration Measures in Tributaries of the Vindel River Catchment2013In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 18, no 3, p. Article Number: UNSP 8-Article in journal (Refereed)
    Abstract [en]

    Some ecological restoration projects include elements of trial and error where new measures are repeatedly tried, evaluated, and modified until satisfactory results are achieved. Thereafter, the resulting methods may be applied on larger scales. A difficult step is judging whether developed "best-practice" methods have become reasonably ecologically functional or whether further experimentation "demonstration" methods can lead to yet better results. Here, we use a stream restoration project as a case study for evaluating methods and abiotic effects and outlining stakeholder support for demonstration restoration measures, rather than only using best-practice methods. Our work was located in the Vindel River system, a free-flowing river that is part of the Natura 2000 network. The river was exploited for timber floating from 1850-1976, and rapids in the main channel and tributaries below timberline were channelized to increase timber transport capacity. Several side channels in multi-channeled rapids were blocked and the flow was concentrated to a single channel from which boulders and large wood were removed. Hence, previously heterogeneous environments were replaced by more homogeneous systems with limited habitat for riverine species. The restoration project strives to alleviate the effects of fragmentation and channelization in affected rapids by returning coarse sediment from channel margins to the main channel. However, only smaller, angular sediment is available given blasting of large boulders, and large (old-growth) wood is largely absent; therefore, original levels of large boulders and large wood in channels cannot be achieved with standard restoration practices. In 10 demonstration sites, we compensated for this by adding large boulders and large wood (i.e., entire trees) from adjacent upland areas to previously best-practice restored reaches and compared their hydraulic characteristics with 10 other best-practice sites. The demonstration sites exhibited significantly reduced and more variable current velocities, and wider channels, but with less variation than pre-restoration. The ecological response to this restoration has not yet been studied, but potential outcomes are discussed.

  • 30. Gonzalez, Eduardo
    et al.
    Felipe-Lucia, Maria R.
    Bourgeois, Berenger
    Boz, Bruno
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palmer, Grant
    Sher, Anna A.
    Integrative conservation of riparian zones2017In: Biological Conservation, ISSN 0006-3207, E-ISSN 1873-2917, Vol. 211, p. 20-29Article in journal (Refereed)
    Abstract [en]

    Riparian zones are the interface between aquatic and terrestrial systems along inland watercourses. They have a disproportionate ecological role in the landscape considering their narrow extent, which makes them a good example of small natural features (sensu Hunter, 2017-in this issue). Characteristically, riparian zones increase species richness in the landscape and provide key services to society, such as soil fertility, water purification, and recreation. Despite the recognized importance of riparian zones for ecological, economic and social reasons, and the vast amount of scientific literature exploring measures for their conservation, current management is still failing at enabling a proper ecological functioning of these areas. The best practices for conservation of riparian zones have mostly focused on manipulating biotic and physical components (e.g. renaturalizing flow regimes, improving channel mobility, and controlling invasions of exotic ecosystem engineer species). However, these strategies face important technical, socio-economic, and legal constraints that require a more integrative approach for effective conservation. In this paper we summarize the main problems affecting riparian zones and their current management challenges. Following Hunter et al. (2017-in this issue), we review novel approaches to conservation of riparian zones, complementary to manipulating processes that reflect contemporary management and policy. These include (1) investing in environmental education for both local people and technical staff, (2) guaranteeing qualitative and long term inventories and monitoring, (3) establishing legislation and solutions to protect riparian zones, (4) framing economic activities in riparian zones under sustainable management, and (5) planning restoration of riparian zones at multiple and hierarchical spatio-temporal scales.

  • 31. Grill, G.
    et al.
    Lehner, B.
    Thieme, M.
    Geenen, B.
    Tickner, D.
    Antonelli, F.
    Babu, S.
    Borrelli, P.
    Cheng, L.
    Crochetiere, H.
    Macedo, H. Ehalt
    Filgueiras, R.
    Goichot, M.
    Higgins, J.
    Hogan, Z.
    Lip, B.
    McClain, M. E.
    Meng, J.
    Mulligan, M.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olden, J. D.
    Opperman, J. J.
    Petry, P.
    Liermann, C. Reidy
    Saenz, L.
    Salinas-Rodriguez, S.
    Schelle, P.
    Schmitt, R. J. P.
    Snider, J.
    Tan, F.
    Tockner, K.
    Valdujo, P. H.
    van Soesbergen, A.
    Zarfl, C.
    Mapping the world's free-flowing rivers2019In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 569, no 7755, p. 215-221Article in journal (Refereed)
    Abstract [en]

    Free-flowing rivers (FFRs) support diverse, complex and dynamic ecosystems globally, providing important societal and economic services. Infrastructure development threatens the ecosystem processes, biodiversity and services that these rivers support. Here we assess the connectivity status of 12 million kilometres of rivers globally and identify those that remain free-flowing in their entire length. Only 37 per cent of rivers longer than 1,000 kilometres remain free-flowing over their entire length and 23 per cent flow uninterrupted to the ocean. Very long FFRs are largely restricted to remote regions of the Arctic and of the Amazon and Congo basins. In densely populated areas only few very long rivers remain free-flowing, such as the Irrawaddy and Salween. Dams and reservoirs and their up- and downstream propagation of fragmentation and flow regulation are the leading contributors to the loss of river connectivity. By applying a new method to quantify riverine connectivity and map FFRs, we provide a foundation for concerted global and national strategies to maintain or restore them.

  • 32. Hagen, Dagmar
    et al.
    Svavarsdottir, Kristin
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Tolvanen, Anne K
    Raulund-Rasmussen, Karsten
    Aradottir, Asa L
    Fosaa, Anna Maria
    Halldorsson, Gudmundur
    Ecological and social dimensions of ecosystem restoration in the nordic countries2013In: Ecology & society, ISSN 1708-3087, E-ISSN 1708-3087, Vol. 18, no 4, p. 34-Article in journal (Refereed)
    Abstract [en]

    An international overview of the extent and type of ecological restoration can offer new perspectives for understanding, planning, and implementation. The Nordic countries, with a great range of natural conditions but historically similar social and political structures, provide an opportunity to compare restoration approaches and efforts across borders. The aim of this study was to explore variation in ecological restoration using the Nordic countries as an example. We used recent national assessments and expert evaluations of ecological restoration. Restoration efforts differed among countries: forest and peatland restoration was most common in Finland, freshwater restoration was most common in Sweden, restoration of natural heathlands and grasslands was most common in Iceland, restoration of natural and semi-cultural heathlands was most common in Norway, and restoration of cultural ecosystems, mainly abandoned agricultural land, was most common in Denmark. Ecological restoration currently does not occur on the Faroe Islands. Economic incentives influence ecological restoration and depend on laws and policies in each country. Our analyses suggest that habitat types determine the methods of ecological restoration, whereas socio-economic drivers are more important for the decisions concerning the timing and location of restoration. To improve the understanding, planning, and implementation of ecological restoration, we advocate increased cooperation and knowledge sharing across disciplines and among countries, both in the Nordic countries and internationally. An obvious advantage of such cooperation is that a wider range of experiences from different habitats and different socio-economic conditions becomes available and thus provides a more solid basis for developing practical solutions for restoration methods and policies.

  • 33.
    Hasselquist, Eliza Maher
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hasselquist, Niles J.
    Sparks, Jed P.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Changes in nitrogen cycling in riparian zones along a chronosequence of restored streams in northern SwedenManuscript (preprint) (Other academic)
    Abstract [en]

    Understanding how stream restoration affects nitrogen (N) cycling in riparian zones is crucial for setting realistic performance criteria for restored streams. Most streams in northern Sweden were channelized for timber floating, and many streams have now been restored. Channelization disconnected streams from the riparian zone, and reduced the flooding that creates anoxic conditions necessary for many N-cycling reactions. We used a space-for-time substitution consisting of stream reaches restored 2 to 25 years ago, unrestored channelized and natural reference reaches to determine how N-cycling in riparian zones changes with time after restoration. Using stable isotopes of N (δ15N), we found that restoration caused more enriched foliar and root δ15N in recently restored sites, suggesting more gaseous losses of N in younger sites. This enrichment in foliar and root δ15N decreased over the 25-year chronosequence suggesting that the N-cycle becomes tighter and loses less N as it ages. Although the [N] in foliage, roots, and soils did not change over time, understory biomass decreased over time, suggesting that more N was available to plants in younger compared to older sites. Changes in the mechanism of N acquisition (i.e., mycorrhizal colonization, as shown by Δδ15N), plant species richness, and cover of deciduous trees (carbon source), were the most important factors explaining variation in δ15N along with time after restoration. It is clear that the restoration of these streams causes a large and rapid change in nitrogen processing in the riparian zone and this alteration persists for at least 25 years.

  • 34.
    Hasselquist, Eliza Maher
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Hasselquist, Niles J.
    Sparks, Jed P.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Recovery of nitrogen cycling in riparian zones after stream restoration using delta N-15 along a 25-year chronosequence in northern Sweden2017In: Plant and Soil, ISSN 0032-079X, E-ISSN 1573-5036, Vol. 410, no 1-2, p. 423-436Article in journal (Refereed)
    Abstract [en]

    Swedish boreal streams were modified to transport timber by pushing boulders to stream sides, creating levees that disconnected streams from riparian areas. Many streams have since been restored and our goal was to understand how this affects riparian nitrogen (N) cycling. We compared the natural abundance of delta N-15 isotopes in foliage and roots of Filipendula ulmaria plus soils and litter along streams restored 2-25 years ago. We measured sources of N, potential immobilization of N, namely plant diversity and biomass, and the amount and sources of carbon (C) to determine if these were important for describing riparian N cycling. The delta N-15 of F. ulmaria foliage changed dramatically just after restoration compared to the channelized, disconnected state and then converged over the next 25 years with the steady-state reference. The disturbance and reconnection of the stream with the riparian zone during restoration created a short-term pulse of N availability and gaseous losses of N as a result of enhanced microbial processing of N. With increasing time since restoration, N availability appears to have decreased, and N sources changed to those derived from mycorrhizae, amino acids, or the humus layer, or there was enhanced N-use efficiency by older, more diverse plant communities.

  • 35.
    Hasselquist, Eliza Maher
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hjalten, Joakim
    Jørgensen, Dolly
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Lind, Lovisa
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Polvi, Lina E.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Time for recovery of riparian plants in restored northern Swedish streams: a chronosequence study2015In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 25, no 5, p. 1373-1389Article in journal (Refereed)
    Abstract [en]

    A lack of ecological responses in stream restoration projects has been prevalent throughout recent literature with many studies reporting insufficient time for recovery. We assessed the relative importance of time, site variables, and landscape setting for understanding how plant species richness and understory productivity recover over time in riparian zones of northern Swedish streams. We used a space-for-time substitution consisting of 13 stream reaches restored 5-25 years ago, as well as five unrestored channelized reference reaches. We inventoried the riparian zone for all vascular plant species along 60-m study reaches and quantified cover and biomass in plots. We found that while species richness increased with time, understory biomass decreased. Forbs made up the majority of the species added, while the biomass of graminoids decreased the most over time, suggesting that the reduced dominance of graminoids favored less productive forbs. Species richness and density patterns could be attributed to dispersal limitation, with anemochorous species being more associated with time after restoration than hydrochorous, zoochorous, or vegetatively reproducing species. Using multiple linear regression, we found that time along with riparian slope and riparian buffer width (e.g., distance to logging activities) explained the most variability in species richness, but that variability in total understory biomass was explained primarily by time. The plant community composition of restored reaches differed from that of channelized references, but the difference did not increase over time. Rather, different time categories had different successional trajectories that seemed to converge on a unique climax community for that time period. Given our results, timelines for achieving species richness objectives should be extended to 25 years or longer if recovery is defined as a saturation of the accumulation of species over time. Other recommendations include making riparian slopes as gentle as possible given the landscape context and expanding riparian buffer width for restoration to have as much impact as possible.

  • 36.
    Hasselquist, Eliza Maher
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Polvi, Lina E
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Kahlert, Maria
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Sandberg, Lisa
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Mckie, Brendan G.
    Contrasting Responses among Aquatic Organism Groups to Changes in Geomorphic Complexity Along a Gradient of Stream Habitat Restoration: Implications for Restoration Planning and Assessment2018In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 10, no 10, article id 1465Article in journal (Refereed)
    Abstract [en]

    Many stream restoration projects aim to increase geomorphic complexity, assuming that this increases habitat heterogeneity and, thus, biodiversity. However, empirical data supporting these linkages remain scant. Previous assessments of stream restoration suffer from incomplete quantification of habitat complexity, or a narrow focus on only one organism group and/or one restoration measure, limiting learning. Based on a comprehensive quantification of geomorphic complexity in 20 stream reaches in northern Sweden, ranging from streams channelized for timber floating to restored and reference reaches, we investigated responses of macroinvertebrates, diatoms, and macrophytes to multiple geomorphic metrics. Sediment size heterogeneity, which was generally improved in restored sites, favored macroinvertebrate and diatom diversity and macroinvertebrate abundance. In contrast, macrophyte diversity responded to increased variation along the longitudinal stream profile (e.g., step-pools), which was not consistently improved by the restoration. Our analyses highlight the value of learning across multiple restoration projects, both in identifying which aspects of restoration have succeeded, and pinpointing other measures that might be targeted during adaptive management or future restoration. Given our results, a combination of restoration measures targeting not only sediment size heterogeneity, but also features such as step-pools and instream wood, is most likely to benefit benthic biota in streams.

  • 37. Helfield, James M
    et al.
    Capon, Samantha J
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Palm, Daniel
    Restoration of rivers used for timber floating: Effects on riparian plant diversity2007In: Ecological Applications, ISSN 1051-0761, Vol. 17, no 3, p. 840-851Article in journal (Refereed)
    Abstract [en]

    Fluvial processes such as flooding and sediment deposition play a crucial role in structuring riparian plant communities. In rivers throughout the world, these processes have been altered by channelization and other anthropogenic stresses. Yet despite increasing awareness of the need to restore natural flow regimes for the preservation of riparian biodiversity, few studies have examined the effects of river restoration on riparian ecosystems. In this study, we examined the effects of restoration in the Ume River system, northern Sweden, where tributaries were channelized to facilitate timber floating in the 19th and early 20th centuries. Restoration at these sites involved the use of heavy machinery to replace instream boulders and remove floatway structures that had previously lined stream banks and cut off secondary channels. We compared riparian plant communities along channelized stream reaches with those along reaches that had been restored 3-10 years prior to observation. Species richness and evenness were significantly increased at restored sites, as were floodplain inundation frequencies. These findings demonstrate how river restoration and associated changes in fluvial disturbance regimes can enhance riparian biodiversity. Given that riparian ecosystems tend to support a disproportionate share of regional species pools, these findings have potentially broad implications for biodiversity conservation at regional or landscape scales.

  • 38.
    Helfield, James M
    et al.
    Department of Environmental Science, Huxley College of the Environment, Western Washington University, Bellingham, Washington 98225-9181 USA.
    Engström, Johanna
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Michel, James T
    Department of Environmental Science, Huxley College of the Environment, Western Washington University, Bellingham, Washington 98225-9181 USA.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of river restoration on riparian biodiversity in secondary channels of the Pite River, Sweden2012In: Environmental Management, ISSN 0364-152X, E-ISSN 1432-1009, Vol. 49, no 1, p. 130-141Article in journal (Other academic)
    Abstract [en]

    Between 1850 and 1970, rivers throughout Sweden were channelized to facilitate timber floating.  Floatway structures were installed to streamline banks and disconnect flow to secondary channels, resulting in simplified channel morphologies and more homogenous flow regimes.  In recent years, local authorities have begun to restore channelized rivers.  In this study, we examined the effects of restoration on riparian plant communities at previously disconnected secondary channels of the Pite River.  We detected no increase in riparian diversity at restored sites relative to unrestored (i.e., disconnected) sites, but we did observe significant differences in species composition of both vascular plant and bryophyte communities.  At disconnected sites, plots closest to the stream featured greater representation of mesic-hydric floodplain species, whereas plots farthest from the stream featured greater representation of mesic-xeric species characteristic of the surrounding upland forest.  In contrast, restored sites were most strongly represented by upland species at all distances relative to the stream.  These patterns suggest that restoration has resulted in increased water levels in reconnected channels, but that the restored fluvial regime has not influenced the development of characteristic flood-adapted plant communities.  This may be due to the short time interval (ca. 5 years) since restoration.  Previous studies have demonstrated relatively quick responses to similar restoration in single-channel tributaries, but secondary channels may respond differently due to the more buffered hydrologic regimes typically seen in anabranching systems.  These findings illustrate how restoration outcomes can vary according to hydrologic, climatic and ecological factors, reinforcing the need for site-specific restoration strategies.

  • 39. Hjalten, Joakim
    et al.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jorgensen, Dolly
    Bell, David
    Forest-Stream Links, Anthropogenic Stressors, and Climate Change: Implications for Restoration Planning2016In: BioScience, ISSN 0006-3568, E-ISSN 1525-3244, Vol. 66, no 8, p. 646-654Article in journal (Refereed)
    Abstract [en]

    The global extraction of forest and water resources has led to habitat degradation, biodiversity loss, and declines in ecosystem services. As a consequence, ecological restoration has become a global priority. Restoration efforts to offset this trend, however, are not always effective. One reason is that many restoration projects target single ecosystems and fail to acknowledge functional links between ecosystems. We synthesized current knowledge on links between forest and stream ecosystems, the effect of anthropogenic stressors on these links, and their implications for restoration planning. Many examples show that lateral subsidies, such as invertebrate prey and nutrients, are important in both terrestrial and aquatic environments. Stressors such as commercial forestry, flow regulation, stream channelization, and climate change affect these links and should be considered in restoration planning. Restoration practitioners are encouraged to view adjacent forest and stream ecosystems as one entity.

  • 40.
    Hof, Anouschka R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Future Climate Change Will Favour Non-Specialist Mammals in the (Sub)Arctics2012In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 7, no 12, p. e52574-Article in journal (Refereed)
    Abstract [en]

    Arctic and subarctic (i.e., [sub] arctic) ecosystems are predicted to be particularly susceptible to climate change. The area of tundra is expected to decrease and temperate climates will extend further north, affecting species inhabiting northern environments. Consequently, species at high latitudes should be especially susceptible to climate change, likely experiencing significant range contractions. Contrary to these expectations, our modelling of species distributions suggests that predicted climate change up to 2080 will favour most mammals presently inhabiting (sub) arctic Europe. Assuming full dispersal ability, most species will benefit from climate change, except for a few cold-climate specialists. However, most resident species will contract their ranges if they are not able to track their climatic niches, but no species is predicted to go extinct. If climate would change far beyond current predictions, however, species might disappear. The reason for the relative stability of mammalian presence might be that arctic regions have experienced large climatic shifts in the past, filtering out sensitive and range-restricted taxa. We also provide evidence that for most (sub) arctic mammals it is not climate change per se that will threaten them, but possible constraints on their dispersal ability and changes in community composition. Such impacts of future changes in species communities should receive more attention in literature.

  • 41.
    Hof, Anouschka R
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Future of biodiversity in the Barents Region2015Book (Other academic)
    Abstract [en]

    Climate change may affect biodiversity to a large extent. Its effects have already caused shifts in species distributions and even species extinctions. Since especially high latitude regions are expected to be affected, this publication assesses the impact of future climate change on the biodiversity in the Barents Region (northern parts of Norway, Sweden and Finland, and Northwest Russia). It reports on the impact of climate change on a large range of species, including amphibians, butterflies, birds, mammals, moths, plants, slugs, snails, and reptiles, of which a few were studied more in depth. It further identifies future hotspots of species diversity and gives recommendations on species that should be prioritized for conservation and on areas that should be included in the network of protected areas in future. Lastly, it provides guidance on which aspects require further study.

  • 42.
    Hof, Anouschka R
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    How biotic interactions may alter future predictions of species distributions: future threats to the persistence of the arctic fox in Fennoscandia2012In: Diversity & distributions: A journal of biological invasions and biodiversity, ISSN 1366-9516, E-ISSN 1472-4642, Vol. 18, no 6, p. 554-562Article in journal (Refereed)
    Abstract [en]

    Aim With climate change, reliable predictions of future species geographic distributions are becoming increasingly important for the design of appropriate conservation measures. Species distribution models (SDMs) are widely used to predict geographic range shifts in response to climate change. However, because species communities are likely to change with the climate, accounting for biotic interactions is imperative. A shortcoming of introducing biotic interactions in SDMs is the assumption that biotic interactions remain the same under changing climatic factors, which is disputable. We explore the performance of SDMs while including biotic interactions.

    Location Fennoscandia, Europe.

    Methods We investigate the appropriateness of the inclusion of biotic factors (predator pressure and prey availability) in assessing the future distribution of the arctic fox (Alopex lagopus) in Fennoscandia by means of SDM, using the algorithm MaxEnt.

    Results Our results show that the inclusion of biotic interactions enhanced the accuracy of SDMs to predict the current arctic fox distribution, and we argue that the accuracy of future predictions might also be enhanced. While the range of the arctic fox is predicted to have decreased by 43% in 2080 because of temperature-related variables, projected increases in predator pressure and reduced prey availability are predicted to constrain the potential future geographic range of the arctic fox in Fennoscandia 13% more.

    Main conclusions The results indicate that, provided one has a good knowledge of past changes and a clear understanding of interactions in the community involved, the inclusion of biotic interactions in modelling future geographic ranges of species increases the predictive power of such models. This likely has far-reaching impacts upon the design and implementation of possible conservation and management plans. Control of competing predators and supplementary feeding are suggested as necessary management actions to preserve the Fennoscandian arctic fox population in the face of climate change.

  • 43.
    Hof, Anouschka R
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The usefulness of elevation as a predictor variable in species distribution modelling2012In: Ecological Modelling, ISSN 0304-3800, E-ISSN 1872-7026, Vol. 246, p. 86-90Article in journal (Refereed)
    Abstract [en]

    Species distribution models (SDMs) are increasingly used to forecast impacts of climate change on species geographic distributions, but the reliability of predictions is scrutinized. The main limitation of SDMs lies in their assumption that species' ranges are determined mostly by climate, which is arguable. For instance, biotic interactions, habitat and elevation may affect species ranges. The inclusion of habitat-related variables as predictors in SDMs is generally accepted, but there is no consensus regarding the inclusion of elevation. A review of randomly chosen literature revealed that elevation is used as a predictor variable by just over half of the papers studied with no apparent trends as to why, except that papers predicting mammal species distributions for large regions included elevation more often than not, and that papers that predicted mammal ranges for small regions tended to exclude elevation. In addition, we compared the performance of SDMs with and without elevation as a predictor variable for the distribution of north European mammals and plants and found that the difference between their performances is statistically significant for mammals, slightly favouring exclusion of elevation. No differences were found for plants.

    (C) 2012 Elsevier B.V. All rights reserved.

  • 44.
    Hof, Anouschka R.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Forest and Wildlife Ecology, University of Wisconsin-Madison, Madison, Wisconsin 53706 USA.
    Rodriguez-Castaneda, Genoveva
    Allen, Andrew M.
    Jansson, Roland
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Vulnerability of Subarctic and Arctic breeding birds2017In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 27, no 1, p. 219-234Article in journal (Refereed)
    Abstract [en]

    Recent research predicts that future climate change will result in substantial biodiversity loss associated with loss of habitat for species. However, the magnitude of the anticipated biodiversity impacts are less well known. Studies of species vulnerability to climate change through species distribution models are often limited to assessing the extent of species' exposure to the consequences of climate change to their local environment, neglecting species sensitivity to global change. The likelihood that species or populations will decline or go extinct due to climate change also depends on the general sensitivity and adaptive capacity of species. Hence, analyses should also obtain more accurate assessments of their vulnerability. We-addressed this by constructing a vulnerability matrix for 180 bird species currently breeding in Subarctic and Arctic Europe that integrates a climatic exposure-based vulnerability index and a natural-history trait-based vulnerability index. Species that may need extra conservation-attention based on our matrix include the Great Snipe (Gallinago media), the Rough-legged Buzzard (Buteo lagopus), the Red-throated Pipit (Anthus cervinus), the Common Swift (Apus apus), the Horned Lark (Eremophila alpestris), and the Bar-tailed Godwit (Limosa lapponica). Our vulnerability matrix stresses the importance of looking beyond exposure to climate change when species conservation is the aim. For the species that scored high in our matrix the future in the region looks grim and targeted conservation actions, incorporating macroecological and global perspectives, may be needed to alleviate severe population declines. We further demonstrate that climate change is predicted to significantly reduce the current breeding range of species adapted to cold climates in Subarctic and Arctic Europe. The number of incubation days and whether the species was a habitat specialist or not were also among the variables most strongly related to predicted contraction or expansion of species' breeding ranges. This-approach may aid the identification of vulnerable bird species worldwide.

  • 45. Hughes, Francine MR
    et al.
    Johansson, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Xiong, Shaojun
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Carlborg, Elisabet
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hawkins, Dawn
    Svedmark, Magnus
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hayes, Adrian
    Goodall, Alexander
    Richards, Keith S
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The influence of hydrological regimes on sex ratios and spatial segregation of the sexes in two dioecious riparian shrub species in northern Sweden2010In: Plant Ecology, ISSN 1385-0237, E-ISSN 1573-5052, Vol. 208, no 1, p. 77-92Article in journal (Refereed)
    Abstract [en]

    River management practices have altered the hydrological regimes of many rivers and also altered the availability of regeneration niches for riparian species. We investigated the impact of changed hydrological regimes on the sex ratios and the Spatial Segregation of the Sexes (SSS) in the dioecious species Salix myrsinifolia Salisb.–phylicifolia L. and S. lapponum L. by studying the free-flowing Vindel River and the regulated Ume River in northern Sweden. We surveyed sex ratios of these species in 12 river reaches on the Vindel River and in 17 reaches on the Ume River. In addition, we surveyed the sex and location above mean river stage of 1,002 individuals across both river systems to investigate the SSS of both species. Cuttings were collected from male and female individuals of S. myrsinifolia–phylicifolia from both rivers and subjected to four different water table regimes in a greenhouse experiment to investigate growth response between the sexes. We found an M/F sex ratio in both river systems similar to the regional norm of 0.62 for S.myrsinifolia–phylicifolia and of 0.42 for S. lapponum. We found no evidence of SSS in either the free-flowing Vindel River or the regulated Ume River. In the greenhouse experiment, hydrological regime had a significant effect on shoot and root dry weight and on root length. Significantly higher shoot dry weights were found in females than in males and significantly different shoot and root dry weights were found between cuttings taken from the two rivers. We concluded that changed hydrological regimes are likely to alter dimensions of the regeneration niche and therefore to influence sex ratios and SSS at an early successional stage, making it difficult to find clear spatial patterns once these species reach maturity and can be sexed.

  • 46.
    Hylander, Kristoffer
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Dynesius, Mats
    Jonsson, Bengt Gunnar
    Nilsson, Christer
    Lie low: substrate form determines the fate of bryophytes in riparian buffer stripsManuscript (preprint) (Other academic)
  • 47.
    Hylander, Kristoffer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Dynesius, Mats
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Jonsson, Bengt Gunnar
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Substrate form determines the fate of bryophytes in riparian buffer strips2005In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 15, no 2, p. 674-688Article in journal (Refereed)
  • 48.
    Hylander, Kristoffer
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Jonsson, Bengt Gunnar
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Evaluating buffer strips along boreal streams using bryophtes as indicators2002In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 12, no 3, p. 797-806Article in journal (Refereed)
    Abstract [en]

    Buffer strips have recently become the main management practice for reducing logging impact on stream habitats in boreal and temperate regions. The habitat value of buffer strips, however, has not received much attention, although riparian forests belong to the systems with the highest biodiversity in these regions. We used plants as indicators of the ability of buffer strips to maintain an environment similar to intact riparian forests in a boreal forest landscape in northern Sweden. We measured the growth of three common bryophyte species (Hylocomiastrum umbratum, Calypogeia integristipula, and Tritomaria quinquedentata) transplanted to riparian habitat close to a stream in clear-cut logged sites 10-15 m wide buffer strips on each side of the stream, and intact (reference) sites. Each of the three site categories included six wet and six tnoist-mesic sites and the experiment was followed over three months in 1999. The species remained vital in the reference sites and grew substantially during the 3-mo-long experiment, but in the logged sites almost no growth was registered, and many shoots died (except for T. qninquedentata). The pattern was consistent irrespective of the ground moisture class. The performance of bryophytes in the moist-mesic buffer strips was almost as bad as in the logged sites, whereas in the wet buffer strips it was either intermediate between that in logged and reference sites (H. umbratum) or very similar to that in reference sites (C. integristipula and T. quinquedentata). The edge effect has previously been shown to vary depending on edge orientation, edge physiognomy, and weather conditions. We found that ground moisture can be of major importance as well. Although many buffer strips function better than no strips, 20-30 m wide strips (with a stream in the middle) through a logged area consist entirely of edge habitat. Increasing the buffer width and avoiding clear-cut logging on both sides of a watercourse would be the first steps to take for improving biodiversity conservation in riparian habitats. Our results also show that bryophytes are good indicators of habitat quality and efficient tools for assessing the ecological function of buffer strips.

  • 49.
    Hylander, Kristoffer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Göthner, Tove
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Effects of buffer strip retention and clearcutting on land snails in boreal riparian forests2004In: Conservation Biology, ISSN 0888-8892, E-ISSN 1523-1739, Vol. 18, no 4, p. 1052-1062Article in journal (Refereed)
    Abstract [en]

    We investigated the short-term effects of forest clearcutting on land snails (terrestrial gastropods) in 15 forest stands along small streams in Sweden. Two different silvicultural treatments were applied at each site: clearcutting across the stream channel and buffer strips 10 m wide on each side of the stream. Additionally, we studied 10 reference sites in unlogged riparian forests along similar-sized streams. All sites were studied before logging and then 2.5 years after logging. After clearcutting the number of individuals in a 0.5-m2 sample from each site decreased on average from 107 to 87, and the mean number of species per sample decreased from 9.9 to 7.7. Most species were negatively affected, but there were also clear differences in sensitivity. There were correlations between species survival and ground moisture. At the wettest clearcut sites with an almost intact bryophyte cover, the land snails were unaffected by clearcutting. This result suggests that wet or moist forest floors can serve as refugia even at very small spatial scales (e.g., shallow hollows, crevices). If this is an important mechanism, the spatial distribution of small habitats could be important for the long-term survival of the snail fauna or other small, dispersal-limited organisms at clearcut sites. In the buffer strips, the number of individuals decreased but not the number of species, indicating that buffer-strip retention is a good practice for protecting land snails in riparian forests. The varying effectiveness of the buffer strip could partly be explained by the proportion of the remaining basal area, emphasizing that buffer strips could be even more effective if efforts are made to avoid heavy damage by windthrows.

  • 50.
    Hylander, Kristoffer
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. Department of Natural and Environmental Sciences, Mittuniversitetet, Sundsvall.
    Jonsson, Bengt Gunnar
    Department of Natural and Environmental Sciences, Mittuniversitetet, Sundsvall.
    Göthner, Tove
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Differences in habitat quality explain nestedness in a land snail meta-community2005In: Oikos, ISSN 0030-1299, E-ISSN 1600-0706, Vol. 108, no 2, p. 351-361Article in journal (Refereed)
    Abstract [en]

    We set up two alternative hypotheses on how environmental variables could foster nestedness; one of “nested habitats” and another of “nested habitat quality”. The former hypothesis refers to situations where the nestedness of species depends on a nestedness of discrete habitats. The latter considers situations where all species in an assemblage increase in abundance along the same environmental gradient, but differ in specialisation or tolerance. We tested whether litter-dwelling land snails (terrestrial gastropods) in boreal riparian forest exhibited a nested community structure, whether such a pattern was related to differences in environmental variables among sites, and which of the two hypotheses that best could account for the found pattern. We sampled litter from 100 m2 plots in 29 mature riparian forest sites along small streams in the boreal zone of Sweden. The number of snail species varied between 3 and 14 per site. Ranking the species-by-site matrix by PCA scores of the first ordination axis revealed a similarly significant nested pattern as when the matrix was sorted by number of species, showing that the species composition in this meta-community can be properly described as nested. Several environmental variables, most notably pH index, were correlated with the first PCA axis. All but two species had positive eigenvectors in the PCA ordination and the abundance increased considerably along the gradient for most of the species implying that the hypothesis of “nested habitats” was rejected in favour of the “nested habitat quality” hypothesis. Analyses of nestedness have seldom been performed on equal sized plots, and our study shows the importance of understanding that variation in environmental variables among sites can result in nested communities. The conservation implications are different depending on which of our two hypotheses is supported; a conservation focus on species “hotspots” is more appropriate if the communities are nested because of “nested habitat quality”.

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