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Nilsson, Christer
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Publications (10 of 131) Show all publications
Sarneel, J. M., Hefting, M. M., Kowalchuk, G. A., Nilsson, C., Van der Velden, M., Visser, E. J. W., . . . Jansson, R. (2019). Alternative transient states and slow plant community responses after changed flooding regimes. Global Change Biology, 25(4), 1358-1367
Open this publication in new window or tab >>Alternative transient states and slow plant community responses after changed flooding regimes
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2019 (English)In: Global Change Biology, ISSN 1354-1013, E-ISSN 1365-2486, Vol. 25, no 4, p. 1358-1367Article in journal (Refereed) Published
Abstract [en]

Climate change will have large consequences for flooding frequencies in freshwater systems. In interaction with anthropogenic activities (flow regulation, channel restoration and catchment land-use) this will both increase flooding and drought across the world. Like in many other ecosystems facing changed environmental conditions, it remains difficult to predict the rate and trajectory of vegetation responses to changed conditions. Given that critical ecosystem services (e.g. bank stabilization, carbon subsidies to aquatic communities or water purification) depend on riparian vegetation composition, it is important to understand how and how fast riparian vegetation responds to changing flooding regimes. We studied vegetation changes over 19 growing seasons in turfs that were transplanted in a full-factorial design between three riparian elevations with different flooding frequencies. We found that (a) some transplanted communities may have developed into an alternative stable state and were still different from the target community, and (b) pathways of vegetation change were highly directional but alternative trajectories did occur, (c) changes were rather linear but faster when flooding frequencies increased than when they decreased, and (d) we observed fastest changes in turfs when proxies for mortality and colonization were highest. These results provide rare examples of alternative transient trajectories and stable states under field conditions, which is an important step towards understanding their drivers and their frequency in a changing world.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
alternative stable states, drought events, flood regime change, hydrological alterations, hysteresis, riparian vegetation, river restoration, species traits
National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-157948 (URN)10.1111/gcb.14569 (DOI)000461817500013 ()30638293 (PubMedID)
Available from: 2019-04-18 Created: 2019-04-18 Last updated: 2019-04-18Bibliographically approved
Su, X., Polvi, L. E., Lind, L., Pilotto, F. & Nilsson, C. (2019). Importance of landscape context for post-restoration recovery of riparian vegetation. Freshwater Biology, 64(5), 1015-1028
Open this publication in new window or tab >>Importance of landscape context for post-restoration recovery of riparian vegetation
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2019 (English)In: Freshwater Biology, ISSN 0046-5070, E-ISSN 1365-2427, Vol. 64, no 5, p. 1015-1028Article in journal (Refereed) Published
Abstract [en]

We tested whether the recovery of riparian vegetation along rapids that have been restored after channelisation for timber floating can be predicted based on floristic and geomorphic characteristics of surrounding landscape units. Our study was located along tributary stream networks, naturally fragmented in rapids, slow-flowing reaches, and lakes (i.e. process domains), in the Vindel River catchment in northern Sweden.

We tested whether landscape characteristics, specifically to what extent the geomorphology (affecting local abiotic conditions), species richness, and species composition (representing the species pool for recolonisation), as well as the proximity to various upstream process domains (determining the dispersal potential), can predict post-restoration recovery of riparian vegetation.

Our results indicate that post-restoration recovery of riparian vegetation richness or composition is not strongly related to landscape-scale species pools in these streams. The restored rapids were most similar to upstream rapids, geomorphically and floristically, including plant traits. Species richness of adjacent landscape units (upstream process domains or lateral upland zone) did not correlate with that of restored rapids, and proximity of upstream rapids or other process domains was only weakly influential, thus diminishing support for the hypothesis that hydrochory or other means of propagule dispersal plays a strong role in riparian vegetation community organisation after restoration in this fragmented stream network.

We conclude that, in these naturally fragmented stream systems with three discrete process domains (rapids, slow-flowing reaches and lakes), hydrochory is probably not the main predictor for short-term riparian vegetation recovery. Therefore, other factors than landscape context can serve in prioritising restoration and, in these systems, local factors are likely to outweigh landscape connectivity in the recovery of riparian vegetation.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
hydrochory, plant dispersal, riparian zone, species pool, streams
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-159391 (URN)10.1111/fwb.13282 (DOI)000466805700016 ()
Available from: 2019-06-10 Created: 2019-06-10 Last updated: 2019-06-10Bibliographically approved
Sarneel, J. M., Bejarano, M. D., van Oosterhout, M. & Nilsson, C. (2019). Local flooding history affects plant recruitment in riparian zones. Journal of Vegetation Science, 30(2), 224-234
Open this publication in new window or tab >>Local flooding history affects plant recruitment in riparian zones
2019 (English)In: Journal of Vegetation Science, ISSN 1100-9233, E-ISSN 1654-1103, Vol. 30, no 2, p. 224-234Article in journal (Refereed) Published
Abstract [en]

Aims: Many rivers across the globe are severely impacted by changed flooding regimes, resulting in drastic shifts in vegetation, but the processes driving the exchange of flood‐sensitive and flood‐tolerant species are understood less. We studied the role of long‐term and recent flooding histories for riparian plant recruitment in response to various changes in flooding regime.

Location: Vindel River catchment (Northern Sweden).

Methods

We experimentally changed long‐term flooding regimes by transplanting turfs between high and low elevations in 2000 and in 2014 (= 8 per treatment). We sowed seeds of five riparian species in both transplanted turfs and non‐transplanted controls and counted seedling numbers over two growing seasons. Further, we inventoried natural seedling frequencies in 190 plots in 19 reaches in 2013 and 2014, and related natural seedling numbers to plot flooding history in the period 2012–2014.

Results: We observed effects of long‐term flooding history in the second year of the transplantation study (2015), but not in the first year. In 2015, turfs transplanted to locations with less flooding resulted in higher plant recruitment while transplantation to sites with more frequent flooding reduced recruitment compared to the controls. Since these differences were only found in recently transplanted turfs and not in older turfs, the legacy effect of long‐term flooding history can be transient. In the field seedling survey, similar differences were found between flooding‐history categories in 2013, but not in 2014, when the moisture conditions of the most recent year determined flooding. Further, lowest seedling numbers were observed when the previous flooding occurred in winter, and higher seedling numbers when floods occurred in spring or not at all.

Conclusions: Both long‐term and recent flooding histories can affect plant recruitment, and their influence should be taken into account when designing restoration projects.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
dispersal filtering, environmental filtering, flood dynamics, historic contingency, legacy effects, plant recruitment window, regime shifts, window of opportunity, zonation
National Category
Forest Science
Identifiers
urn:nbn:se:umu:diva-160317 (URN)10.1111/jvs.12731 (DOI)000466421500005 ()
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-17Bibliographically approved
Grill, G., Lehner, B., Thieme, M., Geenen, B., Tickner, D., Antonelli, F., . . . Zarfl, C. (2019). Mapping the world's free-flowing rivers. Nature, 569(7755), 215-221
Open this publication in new window or tab >>Mapping the world's free-flowing rivers
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2019 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 569, no 7755, p. 215-221Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Nature Publishing Group, 2019
National Category
Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:umu:diva-159606 (URN)10.1038/s41586-019-1111-9 (DOI)000467473600041 ()31068722 (PubMedID)
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-17Bibliographically approved
Jansson, R., Ström, L. & Nilsson, C. (2019). Smaller future floods imply less habitat for riparian plants along a boreal river. Ecological Applications
Open this publication in new window or tab >>Smaller future floods imply less habitat for riparian plants along a boreal river
2019 (English)In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582Article in journal (Refereed) Epub ahead of print
Abstract [en]

Climate-change projections suggest large changes in riverine flow regime, which will likely alter riparian communities. In northern Europe, forecasts propose lower annual spring flood peaks and higher winter flows, resulting in narrower riparian zones. To estimate the impact of climate change on habitat extent of riparian plants, we developed a framework estimating the sensitivity and exposure of individual species to streamflow change, and surveyed five reaches along the free-flowing Vindel River in northern Sweden. We modeled the hydrologic niche of riparian plant species based on the probability of occurrence along gradients of flood frequency and duration and used predicted future water-level fluctuations (based on climate models and IPCC emission scenarios) to calculate changes in flow-related habitat availability of individual species. Despite projected increases in runoff, we predict most species to decrease in riparian elevational extent by on average 12-29% until the end of the century, depending on scenario. Species growing in the upper, spring-flood-controlled part of the riparian zone will likely lose most habitat, with the largest reductions in species with narrow ranges of inundation duration tolerance (decreases of up to 54%). In contrast, the elevational extent of most amphibious species is predicted to increase, but conditions creating isoetid vegetation will become rarer or disappear: isoetid vegetation is presently found in areas where ice formed in the fall settles on the riverbank during the winter as water levels subside. Higher winter flows will make these conditions rare. We argue that our framework is useful to project the effects of hydrologic change caused by climate change as well as other stressors such as flow regulation also in other regions. With few rivers remaining unaffected by dams and other human stressors, these results call for monitoring to detect species declines. Management to alleviate species losses might include mitigation of habitat degradation from land-use activities, more environmentally friendly flow schemes, and more intensive management options such as mowing riparian meadows no longer regularly maintained by recurrent floods.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
climate change, flooding, inundation, niche width, riverbanks, river, water table
National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-162858 (URN)10.1002/eap.1977 (DOI)000481122800001 ()31323161 (PubMedID)
Available from: 2019-09-06 Created: 2019-09-06 Last updated: 2019-09-06
Su, X., Lind, L., Polvi, L. E. & Nilsson, C. (2019). Variation in hydrochory among lakes and streams: effects of channel planform, roughness, and currents. Ecohydrology, 12(5), Article ID e2091.
Open this publication in new window or tab >>Variation in hydrochory among lakes and streams: effects of channel planform, roughness, and currents
2019 (English)In: Ecohydrology, ISSN 1936-0584, E-ISSN 1936-0592, Vol. 12, no 5, article id e2091Article in journal (Refereed) Published
Abstract [en]

The configuration of channels in stream networks is vital for their connectivity, biodiversity, and metacommunity dynamics. We compared the capacity of three process domains-lakes, slow-flowing reaches, and rapids-to disperse and retain plant propagules by releasing small wooden cubes as propagule mimics during the spring flood and recording their final locations. We also measured the geomorphic characteristics (planform, longitudinal profile, cross-sectional morphology, and wood) of each process domain. The three process domains all differed in morphology and hydraulics, and those characteristics were important in shaping the transport capacity of mimics. On average, lakes retained more mimics than slow-flowing reaches but did not differ from the retainment of rapids. Living macrophytes were the most efficient element trapping mimics. In rapids and slow-flowing reaches, most trapped mimics remained floating, whereas in lakes, most mimics ended up on the banks. The decay curves of retention varied substantially among and within process domains. The results suggest that managers who rely on natural recovery of restored sites by means of plant immigration may benefit from understanding landscape patterns when deciding upon the location of restoration measures in stream networks.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
connectivity, hydrochory, lakes, northern Sweden, process domains, propagule mimics, streams
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-161838 (URN)10.1002/eco.2091 (DOI)000474658500011 ()
Available from: 2019-08-08 Created: 2019-08-08 Last updated: 2019-08-08Bibliographically approved
Hasselquist, E. M., Polvi, L. E., Kahlert, M., Nilsson, C., Sandberg, L. & Mckie, B. G. (2018). Contrasting Responses among Aquatic Organism Groups to Changes in Geomorphic Complexity Along a Gradient of Stream Habitat Restoration: Implications for Restoration Planning and Assessment. Water, 10(10), Article ID 1465.
Open this publication in new window or tab >>Contrasting Responses among Aquatic Organism Groups to Changes in Geomorphic Complexity Along a Gradient of Stream Habitat Restoration: Implications for Restoration Planning and Assessment
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2018 (English)In: Water, ISSN 2073-4441, E-ISSN 2073-4441, Vol. 10, no 10, article id 1465Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
MDPI, 2018
Keywords
bioassessment, boreal, bryophyte, hydromorphology, riparian, river, substrate heterogeneity, woody bris
National Category
Environmental Sciences related to Agriculture and Land-use
Identifiers
urn:nbn:se:umu:diva-154362 (URN)10.3390/w10101465 (DOI)000451208400180 ()2-s2.0-85054984343 (Scopus ID)
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2018-12-17Bibliographically approved
Nilsson, C., Riis, T., Sarneel, J. M. & Svavarsdóttir, K. (2018). Ecological Restoration as a Means of Managing Inland Flood Hazards. BioScience, 68(2), 89-99
Open this publication in new window or tab >>Ecological Restoration as a Means of Managing Inland Flood Hazards
2018 (English)In: BioScience, ISSN 0006-3568, E-ISSN 1525-3244, Vol. 68, no 2, p. 89-99Article in journal (Refereed) Published
Abstract [en]

Many streams and rivers experience major floods. Historically, human societies have responded to such floods by moving away from them or by abating them, the latter with large negative impacts on stream and river ecology. Societies are currently implementing a strategy of "living with floods,"which may involve ecological restoration. It further involves flood mapping, forecasting, and warning systems. We evaluate 14 different stream-and river-restoration measures, which differ in their capacity to modify water retention and runoff. We discuss these restoration measures in the light of predicted changes in climate and flooding and discuss future restoration needs. We focus on the Nordic countries, where substantial changes in the water cycle are foreseen. We conclude that sustainable solutions require researchers to monitor the effect of flood management and study the relative importance of individual restoration measures, as well as the side effects of flood attenuation.

Place, publisher, year, edition, pages
Oxford University Press, 2018
Keywords
climate change, restoration/remediation, river ecology, ecosystem engineering, hydrology
National Category
Ecology Climate Research Environmental Sciences Oceanography, Hydrology and Water Resources
Identifiers
urn:nbn:se:umu:diva-145379 (URN)10.1093/biosci/bix148 (DOI)000424878000006 ()
Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2019-04-18Bibliographically approved
Pilotto, F., Nilsson, C., Polvi, L. E. & McKie, B. G. (2018). First signs of macroinvertebrate recovery following enhanced restoration of boreal streams used for timber floating. Ecological Applications, 28(2), 587-597
Open this publication in new window or tab >>First signs of macroinvertebrate recovery following enhanced restoration of boreal streams used for timber floating
2018 (English)In: Ecological Applications, ISSN 1051-0761, E-ISSN 1939-5582, Vol. 28, no 2, p. 587-597Article in journal (Refereed) Published
Abstract [en]

Although ecological restoration generally succeeds in increasing physical heterogeneity, many projects fail to enhance biota. Researchers have suggested several possible explanations, including insufficient restoration intensity, or time-lags in ecological responses that prevent detection of significant changes in short-term monitoring programs. This study aims to evaluate whether benthic macroinvertebrate communities responded to an expanded set of stream restoration measures within a study period of one to five years after completion of the restoration project. We studied 10 forest streams in northern Sweden that were channelized in the past for timber floating. Managers subjected six of these streams to habitat restoration, on each of these we selected two reaches, located in close proximity but differing in restoration intensity. In basic restored reaches, the restoration managers broke up the channelized banks and returned cobbles and small boulders to the main channel. In enhanced restoration reaches, they added additional large wood and boulders to reaches previously subjected to basic restoration, and rehabilitated gravel beds. The remaining four streams were not restored, and thus represent the baseline impacted (channelized) condition. We surveyed stream benthic assemblages before the enhanced restoration (year 2010) and three times afterward between 2011 and 2015. Five years after restoration, macroinvertebrate assemblages at the enhanced restored reaches were more differentiated from channelized conditions than those at basic-restored reaches. This reflected increased relative abundances of the insect orders Ephemeroptera and Trichoptera and the bivalve molluscs Sphaeriidae and decreased relative abundances of Chironomidae (Diptera). Analysis of functional traits provided further insights on the mechanistic explanations driving the recovery, e.g., indicating that the augmented channel retention capacity at enhanced restored reaches favored taxa adapted to slow flow conditions and more effectively retained passive aquatic dispersers. The increased restoration intensity in enhanced restored reaches has resulted in shifts in the composition of benthic macroinvertebrate assemblages, including increases in more sensitive taxa. These shifts became fully apparent five years after the enhanced restoration. Our results emphasize the value of longer-term monitoring to assess ecological responses following restoration, and of undertaking additional restoration as a valuable management option for previously restored sites that failed to achieve biotic recovery.

Keywords
community composition, enhanced restoration, heterogeneity, invertebrates, physical complexity, storation intensity, river restoration, timber floating, time since restoration, traits
National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-146229 (URN)10.1002/eap.1672 (DOI)000426499100024 ()29280235 (PubMedID)
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-06-09Bibliographically approved
Bejarano, M. D., Nilsson, C. & Aguiar, F. C. (2018). Riparian plant guilds become simpler and most likely fewer following flow regulation. Journal of Applied Ecology, 55(1), 365-376
Open this publication in new window or tab >>Riparian plant guilds become simpler and most likely fewer following flow regulation
2018 (English)In: Journal of Applied Ecology, ISSN 0021-8901, E-ISSN 1365-2664, Vol. 55, no 1, p. 365-376Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Wiley-Blackwell Publishing Inc., 2018
Keywords
flow regulation, fluvial ecosystem management, functional diversity, guilds, plant traits, riparian vegetation, riverine ecosystems, rivers, Sweden
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-143633 (URN)10.1111/1365-2664.12949 (DOI)000417764600036 ()
Available from: 2018-01-29 Created: 2018-01-29 Last updated: 2018-08-20Bibliographically approved
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