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  • 1251.
    Yashiro, Yuichiro
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Shizu, Yoko
    Hirota, Mitsuru
    Shimono, Ayako
    Ohtsuka, Toshiyuki
    The role of shrub (Potentilla fruticosa) on ecosystem CO2 fluxes in an alpine shrub meadow2010In: Journal of Plant Ecology, ISSN 1752-9921, E-ISSN 1752-993X, Vol. 3, no 2, p. 89-97Article in journal (Refereed)
    Abstract [en]

    Aims Recent studies have shown that alpine meadows on the Qinghai-Tibetan plateau act as significant CO2 sinks. On the plateau, alpine shrub meadow is one of typical grassland ecosystems. The major alpine shrub on the plateau is Potentilla fruticosa L. (Rosaceae), which is distributed widely from 3 200 to 4 000 m. Shrub species play an important role on carbon sequestration in grassland ecosystems. In addition, alpine shrubs are sensitive to climate change such as global warming. Considering global warming, the biomass and productivity of P. fruticosa will increase on Qinghai-Tibetan Plateau. Thus, understanding the carbon dynamics in alpine shrub meadow and the role of shrubs around the upper distribution limit at present is essential to predict the change in carbon sequestration on the plateau. However, the role of shrubs on the carbon dynamics in alpine shrub meadow remains unclear. The objectives of the present study were to evaluate the magnitude of CO2 exchange of P. fruticosa shrub patches around the upper distribution limit and to elucidate the role of P. fruticosa on ecosystem CO2 fluxes in an alpine meadow. Methods We used the static acrylic chamber technique to measure and estimate the net ecosystem productivity (NEP), ecosystem respiration (Re), and gross primary productivity (GPP) of P. fruticosa shrub patches at three elevations around the species' upper distribution limit. Ecosystem CO2 fluxes and environmental factors were measured from 17 to 20 July 2008 at 3 400, 3 600, and 3 800 m a.s.l. We examined the maximum GPP at infinite light (GPP(max)) and maximum R-e (R-emax) during the experimental time at each elevation in relation to aboveground biomass and environmental factors, including air and soil temperature, and soil water content. Important Findings Patches of P. fruticosa around the species' upper distribution limit absorbed CO2, at least during the daytime. Maximum NEP at infinite light (NEPmax) and GPP(max) of shrub patches in the alpine meadow varied among the three elevations, with the highest values at 3 400 m and the lowest at 3 800 m. GPP(max) was positively correlated with the green biomass of P. fruticosa more strongly than with total green biomass, suggesting that P. fruticosa is the major contributor to CO2 uptake in the alpine shrub meadow. Air temperature influenced the potential GPP at the shrub-patch scale. R-max was correlated with aboveground biomass and R-emax normalized by aboveground biomass was influenced by soil water content. Potentilla fruticosa height (biomass) and frequency increased clearly as elevation decreased, which promotes the large-scale spatial variation of carbon uptake and the strength of the carbon sink at lower elevations.

  • 1252.
    Ylva, Karlberg
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    The influence of northern pike on the diet of Eurasian perch2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Top predators in aquatic ecosystems often have strong top-down effects on the ecosystem. Northern pike (Esox lucius) has been documented to cause whitefish (Coregonus lavaretus) populations to diverge into different ecomorphs. This can facilitate piscivory in other predators as a novel resource becomes available to them in the form of dwarf whitefish. The aim of this study is to examine whether the presence of pike causes Eurasian perch (Perca fluviatilis) to shift their diet from insectivory to piscivory, and whether this is directly driven by whitefish polymorphism. Stomach contents of 147 perch from lakes with and without pikes were analyzed. The results show that the presence of pike has a clear influence on the diet of the perch. In lakes without pike, perch are mostly insectivorous, and in lakes with pike, they are mostly piscivorous. This diet shift appears to be driven by whitefish availability, as a majority of the diet of perch in pike lakes consisted of whitefish, while none of the fish eaten by perch in non-pike lakes was whitefish. In addition, the results showed that perch undergo the diet shift from insectivory to piscivory at a smaller size when coexisting with pike. This study can be added to the growing body of evidence for the ecological significance of pike.

  • 1253. Ylänne, Henni
    et al.
    Olofsson, Johan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Oksanen, Lauri
    Stark, Sari
    Consequences of grazer-induced vegetation transitions on ecosystem carbon storage in the tundra2018In: Functional Ecology, ISSN 0269-8463, E-ISSN 1365-2435, Vol. 32, no 4, p. 1091-1102Article in journal (Refereed)
    Abstract [en]

    1. Large herbivores can control plant community composition and, under certain conditions, even induce vegetation shifts to alternative ecosystem states. As different plant assemblages maintain contrasting carbon (C) cycling patterns, herbivores have the potential to alter C sequestration at regional scales. Their influence is of particular interest in the Arctic tundra, where a large share of the world's soil C reservoir is stored.

    2. We assessed the influence of grazing mammals on tundra vegetation and C stocks by resampling two sites located along pasture rotation fences in northern Norway. These fences have separated lightly grazed areas from heavily grazed areas (in close proximity to the fences) and moderately grazed areas (further away from the fences) for the past 50years. Fourteen years earlier, the lightly and moderately grazed areas were dominated by dwarf shrubs, whereas heavy grazing had promoted the establishment of graminoid-dominated vegetation. Since then, both reindeer densities and temperatures have increased, and more time has passed for transient dynamics to be expressed. We expected that the vegetation and C stocks would have changed under all grazing intensities, but not necessarily in the same way.

    3. At the site where relative reindeer numbers and trampling intensity had increased the most, graminoid-dominated vegetation was now also found in the moderately grazed area. At the other site, the dominant vegetation types under all grazing intensities were the same as 14 years earlier.

    4. We show that the heavily grazed, graminoid-dominated areas stored less C above-ground than the lightly grazed, shrub-dominated areas. Yet, the below-ground consequences of grazing-induced grassification varied between the sites: Grazing did not alter organic soil C stocks at the site where both evergreen and deciduous shrubs were abundant in the lightly grazed area, whereas heavy grazing increased organic soil C stocks at the site where the deciduous shrub Betula nana was dominant.

    5. Our results indicate that, despite the negative impacts of grazers on above-ground C storage, their impact on below-ground C may even be positive. We suggest that the site-specific responses of organic soil C stocks to grazing could be explained by the differences in vegetation under light grazing. This would imply that the replacement of deciduous shrubs by graminoids, as a consequence of grazing could be beneficial for C sequestration in tundra soils.

  • 1254.
    Yoo, Kyungsoo
    et al.
    Department of Soil, Water, and Climate, University of Minnesota–Twin Cities, St. Paul, Minnesota, USA.
    Ji, Junling
    Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware, USA.
    Aufdenkampe, Anthony
    Stroud Water Research Center, Avondale, Pennsylvania, USA.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Rates of soil mixing and associated carbon fluxes in a forest vs. tilled agricultural field:  Implications for modeling the soil carbon cycle2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, no G01014Article in journal (Refereed)
    Abstract [en]

    In natural ecosystems, bioturbation is an essential component of soil formation, whereas tillage drives soil mixing in agricultural soils. Yet soil mixing is commonly neglected in modeling soil organic carbon (SOC) as it responds to land use changes. Here, in order to determine mixing-driven carbon fluxes, we combine a mass balance model with measurements of 210Pb activities and SOC contents. Soil mixing rates by tillage decrease from 3.4 ± 2.3 cm yr−1 at the surface to 0.8 ± 0.2 cm yr−1 at a depth of ∼20 cm, causing the SOC stored in the upper 25 cm of the soil to be physically turned over via mixing annually. In contrast, the bioturbation-driven soil mixing velocity at the forest increases from 0.6 ± 0.1 cm yr−1 at the surface to 2.7 ± 0.5 cm yr−1 at a depth of ∼10 cm, which results in physically turning over SOC in the A horizon via mixing on years to decadal time scales. Therefore, SOC fractions with different susceptibilities to decomposition may have significantly different physical trajectories within the soils over their lifespans, and thus the assumption of C-cycling models that all SOC fractions experience identical environmental conditions is unlikely to be realistic. Carbon sinks, excesses of plant carbon inputs over decomposition carbon losses, are found within the top portion of the A horizons. These carbon excesses are transferred, via mixing, to the lower portion of the A horizon, where they are decomposed. By quantifying mixing-derived SOC fluxes, this study shows a previously unrecognized complexity in understanding SOC dynamics associated with land use changes.

  • 1255. Young, Amanda B.
    et al.
    Cairns, David M.
    Lafon, Charles W.
    Moen, Jon
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Geometrid moth outbreaks and their climatic relations in northern Sweden2014In: Arctic, Antarctic and Alpine research, ISSN 1523-0430, E-ISSN 1938-4246, Vol. 46, no 3, p. 659-668Article in journal (Refereed)
    Abstract [en]

    The alpine treeline in northern Fennoscandia is composed primarily of mountain birch (Betula pubescens ssp. czerepanovii), a deciduous tree that experiences episodic defoliation due to outbreaks of the autumnal moth (Epirrita autumnata) and winter moth (Operophtera brumata). Here, we use an extensive dendroecological data set to reconstruct historic defoliating outbreaks and relate them to climatic conditions. Our data are from 25 sites in eight valleys in northern Sweden. We used the computer program OUTBREAK to reconstruct moth outbreaks. The reconstructed outbreak record matches the historical record well. There is a significant, but weak relationship between the outbreak severity and temperatures in February, April, July, and August of the outbreak year. Temperatures in the previous May and November were also positively correlated with outbreak severity. For seasonally aggregated temperatures, only autumn temperatures are correlated with outbreak severity. There was no significant correlation between NAO index and outbreak severity. A spatiotemporal semivariogram analysis showed that sites within approximately 100 km of each other show similar patterns in outbreak severity. Our analyses suggest that moths are affected by climatic variations. The influence of climate on outbreaks is weak because background climatic conditions alone cannot induce an outbreak. Outbreaks also depend on nonclimatic factors, such as tree age, and the outbreak status of neighboring areas.

  • 1256.
    Zackrisson, O
    et al.
    Swedish University of Agricultural Sciences Department of Forest Ecology and Management, Umeå, Sweden.
    Deluca, T
    Swedish University of Agricultural Sciences Department of Forest Ecology and Management, Umeå, Sweden.
    Gentili, Francesco
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Sellstedt, Anita
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Jäderlund, A
    Swedish University of Agricultural Sciences Department of Forest Ecology and Management, Umeå, Sweden.
    Nitrogen fixation in mixed Hylocomium splendens moss communities2009In: Oecologia, ISSN 0029-8549, E-ISSN 1432-1939, Vol. 160, no 2, p. 309-319Article in journal (Refereed)
    Abstract [en]

    The pleurocarpus feather moss, Hylocomium splendens, is one of two co-dominant moss species in boreal forest ecosystems and one of the most common mosses on earth, yet little is known regarding its capacity to host cyanobacterial associates and thus contribute total ecosystem N. In these studies, we evaluated the N-fixation potential of the H. splendens-cyanobacteria association and contrasted the N-fixation activity with that of the putative N-fixing moss-cyanobacteria association of Pleurozium schreberi. Studies were conducted to: quantify N-fixation in H. splendens and P. schreberi in sites ranging from southern to northern Fennoscandia; assess N and P availability as drivers of N-fixation rates; contrast season-long N-fixation rates for both mosses; and characterize the cyanobacteria that colonize shoots of H. splendens. Nitrogen-fixation rates were generally low at southern latitudes and higher at northern latitudes (64-69 degrees N) potentially related to anthropogenic N deposition across this gradient. Nitrogen fixation in H. splendens appeared to be less sensitive to N deposition than P. schreberi. The season-long assessment of N-fixation rates at a mixed feather moss site in northern Sweden showed that H. splendens fixed a substantial quantity of N, but about 50% less total N compared to the contribution from P. schreberi. In total, both species provided 1.6 kg fixed N ha(-1) year(-1). Interestingly, H. splendens demonstrated somewhat higher N-fixation rates at high fertility sites compared to P. schreberi. Nostoc spp. and Stigonema spp. were the primary cyanobacteria found to colonize H. splendens and P. schreberi. These results suggest that H. splendens with associated Nostoc or Stigonema communities contributes a significant quantity of N to boreal forest ecosystems, but the contribution is subordinate to that of P. schreberi at northern latitudes. Epiphytic cyanobacteria are likely a key factor determining the co-dominant presence of these two feather mosses across the boreal biome.

  • 1257. Zhang, Feng
    et al.
    Zhou, Guangsheng
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Remote estimation of the fraction of absorbed photosynthetically active radiation for a maize canopy in Northeast China2015In: Journal of Plant Ecology, ISSN 1752-9921, E-ISSN 1752-993X, Vol. 8, no 4, p. 429-435Article in journal (Refereed)
    Abstract [en]

    Aims Accurate remote estimation of the fraction of absorbed photosynthetically active radiation (fAPAR) is essential for the light use efficiency (LUE) models. Currently, one challenge for the LUE models is lack of knowledge about the relationship between fAPAR and the normalized difference vegetation index (NDVI). Few studies have tested this relationship against field measurements and evaluated the accuracy of the remote estimation method. This study aimed to reveal the empirical relationship between NDVI and fAPAR and to improve algorithms for remote estimation of fAPAR.

    Methods To investigate the method of remote estimation of fAPAR seasonal dynamics, the CASA (Carnegie-Ames-Stanford Approach) model and spectral vegetation indices (VIs) were used for in situ measurements of spectral reflectance and fAPAR during the growing season of a maize canopy in Northeast China.

    Important Findings The results showed that the fAPAR increased rapidly with the day of year during the vegetative stage, it remained relatively stable at the stage of reproduction, and finally decreased slowly during the senescence stage. In addition, fAPAR(green) [fAPAR(green) = fAPAR x (green LAI/green LAI(max))] showed clearer seasonal trends than fAPAR. The NDVI, red-edge NDVI, wide dynamic range vegetation index, red-edge position (REP) and REP with Sentinel-2 bands derived from hyperspectral remote sensing data were all significantly positively related to fAPAR(green) during the entire growing season. In a comparison of the predictive performance of VIs for the whole growing season, REP was the most appropriate spectral index, and can be recommended for monitoring seasonal dynamics of fAPAR in a maize canopy.

  • 1258. Zhang, Feng
    et al.
    Zhou, Guangsheng
    Wang, Yu
    Yang, Fulin
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Evapotranspiration and crop coefficient for a temperate desert steppe ecosystem using eddy covariance in Inner Mongolia, China2012In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 26, no 3, p. 379-386Article in journal (Refereed)
    Abstract [en]

    Evapotranspiration (ET), which links water, energy and the carbon cycle in terrestrial ecosystems, is an important eco-hydrological process, especially in arid and semi-arid regions. To determine the crop coefficient (K-c) over a 2-year period for a temperate desert steppe in Inner Mongolia, China, ET was measured using the eddy covariance method and the reference evapotranspiration (ET0) was estimated from site meteorological data. The results showed that the seasonal variation of ET differed on an annual timescale between the 2 consecutive years, exhibiting a multi-peak curve in 2008 and a single peak in 2009. The mean daily K-c values were 0.15 and 0.17 in 2 years, varying from 0.009 to 0.75 in 2008 and from 0.005 to 0.58 in 2009. The 5-day moving average for K-c values was mainly affected by SWC10cm and R-n, and the regression coefficients (R-2) were 58.9 and 69.5%, respectively. These results will aid in making accurate and quantitative assessments of the vulnerability of the sparse vegetation to climate change.

    Copyright (C) 2011 John Wiley & Sons, Ltd.

  • 1259.
    Zhang, Lai
    et al.
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics. Technical University of Denmark, Denmark ; International Institute for Applied Systems Analysis, Laxenburg, Austria.
    Andersen, Ken H.
    Dieckmann, Ulf
    Brannstrom, Ake
    Four types of interference competition and their impacts on the ecology and evolution of size-structured populations and communities2015In: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 380, p. 280-290Article in journal (Refereed)
    Abstract [en]

    We investigate how four types of interference competition which alternatively affect foraging, metabolism, survival, and reproduction impact the ecology and evolution of size-structured populations. Even though all four types of interference competition reduce population biomass, interference competition at intermediate intensity sometimes significantly increases the abundance of adult individuals and the population's reproduction rate. We find that foraging and metabolic interference evolutionarily favor smaller maturation size when interference is weak and larger maturation size when interference is strong. The evolutionary response to survival interference and reproductive interference is always larger maturation size. We also investigate how the four types of interference competition impact the evolutionary dynamics and resultant diversity and trophic structure of size-structured communities. Like other types of trait-mediated competition, all four types of interference competition can induce disruptive selection and thus promote initial diversification. Even though foraging interference and reproductive interference are more potent in promoting initial diversification, they catalyze the formation of diverse communities with complex trophic structure only at high levels of interference intensity. By contrast, survival interference does so already at intermediate levels, while reproductive interference can only support relatively smaller communities with simpler trophic structure. Taken together, our results show how the type and intensity of interference competition jointly affect coexistence patterns in structured population models. (C) 2015 Elsevier Ltd. All rights reserved.

  • 1260.
    Zhang, Lai
    et al.
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics. School of Mathematical Science, Yangzhou University, Si Wang Ting Road, Yangzhou 225002, People’s Republic of China.
    Takahashi, Daisuke
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Hartvig, Martin
    Andersen, Ken H.
    Food-web dynamics under climate change2017In: Proceedings of the Royal Society of London. Biological Sciences, ISSN 0962-8452, E-ISSN 1471-2954, Vol. 284, no 1867, article id 20171772Article in journal (Refereed)
    Abstract [en]

    Climate change affects ecological communities through its impact on the physiological performance of individuals. However, the population dynamic of species well inside their thermal niche is also determined by competitors, prey and predators, in addition to being influenced by temperature changes. We use a trait-based food-web model to examine how the interplay between the direct physiological effects from temperature and the indirect effects due to changing interactions between populations shapes the ecological consequences of climate change for populations and for entire communities. Our simulations illustrate how isolated communities deteriorate as populations go extinct when the environment moves outside the species' thermal niches. High-trophic-level species are most vulnerable, while the ecosystem function of lower trophic levels is less impacted. Open communities can compensate for the loss of ecosystem function by invasions of new species. Individual populations show complex responses largely uncorrelated with the direct impact of temperature change on physiology. Such complex responses are particularly evident during extinction and invasion events of other species, where climaticallywell-adapted species may be brought to extinction by the changed food-web topology. Our results highlight that the impact of climate change on specific populations is largely unpredictable, and apparently well-adapted species may be severely impacted.

  • 1261. Zhao, Qiong
    et al.
    Sundqvist, Maja K.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. The Center for Macroecology, Evolution and Climate, The Natural History Museum of Denmark, University of Copenhagen,Universitetsparken 15, 2100 Copenhagen Ø Denmark.
    Newman, Gregory S.
    Classen, Aimée T.
    Soils beneath different arctic shrubs have contrasting responses to a natural gradient in temperature2018In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 9, no 6, article id e02290Article in journal (Refereed)
    Abstract [en]

    Shrubs commonly form islands of fertility and are expanding their distribution and dominance in the arctic due to climate change, yet how soil properties may be influenced when different species of shrubs expand under warmer climates remains less explored. Important plant traits, such as their associated root community, are linked to functionally different and dominant shrub species in the arctic and these traits likely shape biogeochemical cycling in areas of shrub expansion. Using an elevational gradient as a proxy for warming, we explored how biochemical processes beneath two important arctic shrubs varied under warmer (low elevation) and cooler (high elevation) climates. Interestingly, the influence of elevation on biogeochemistry varied between the two shrubs. At the low elevation, Betula nana L., an ectomycorrhizal shrub, had high carbon (C) degrading enzyme activities, and relatively low potential net nitrogen (N) mineralization rates. Conversely, Empetrum nigrum ssp. hermaphroditum Hagerup, an cricoid mycorrhizal dwarf-shrub, had higher enzyme activities and net N immobilization rates at the higher elevation. Further, E. nigrum ssp. hermpahroditum appeared to have a more closed C and nutrient cycle than B. nana-enzymes degrading C, N, and phosphorus were tightly correlated with each other and with total C and ammonium concentrations in the humus beneath E. nigrum ssp. hermaphroditum, but not beneath B. nana. Our results suggest differences in the warming responses of C and N cycling beneath shrub species across an arctic tundra landscape.

  • 1262.
    Zindel, Renate
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    The importance of climate and latitude to seed quality from European forest herbs2007Independent thesis Basic level (degree of Bachelor), 20 credits / 30 HE creditsStudent thesis
  • 1263.
    Zinko, Ursula
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Plants go with the flow: predicting spatial distribution of plant species in the boreal forest2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The main objectives of this thesis are to study if a topographic wetness index (TWI) could be used as a tool for predicting the spatial distribution of vascular plant species richness in the boreal forest as well as to study congruence in species richness between vascular plants, liverworts, mosses and lichens. A wetness index ln(a/tanβ) based on topography was used to assign a specific TWI-value to every 20 x 20m grid in two 25 km2 boreal forest landscapes (differing in average soil pH) in northern Sweden. Soil pH is known to be influenced by groundwater and to affect plant species richness in other biomes. Therefore, the relationships between plant species richness, TWI and soil pH were also studied.

    The results showed that the majority of the investigated boreal forest landscapes were relatively dry and species-poor, whereas interspersed patches linked to areas with relatively high TWI had species-rich vegetation including the species of the drier parts of the landscape. There was a positive relationship between species richness of vascular plants and the TWI in both landscapes, but varied with average soil pH. TWI explained 30 % and 52 % of the variation in plant species richness in the landscape with lower and higher pH, respectively. The proportion of regionally uncommon plants also increased with TWI. Testing different calculation methods of the TWI resulted in a large variation in correlation strengths between the various TWI-values and different measured variables (species richness of vascular plants, soil pH, groundwater flow and soil moisture). The relationship between plant species richness and TWI could be further improved with some of the calculation methods.

    When studying correlations in species richness using data sets from boreal forest in northern Sweden, strong positive correlations among vascular plants, mosses and liverworts were found, but no significant correlation between macrolichens and any of the other groups. This result could be explained by that the species number of each of the three related groups increases with ambient moisture, whereas the species number of macrolichens is weakly associated with moisture.

    In conclusion, the TWI could become a useful tool in conservation management for identifying areas of special interest prior to field inventories. Since vascular plants can be used as an indicator taxon for species richness of mosses and liverworts, high TWI-values indicate areas of species hotspots of these taxa.

  • 1264.
    Zinko, Ursula
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Dynesius, Mats
    Nilsson, Christer
    Seibert, Jan
    The importance of soil moisture and pH for the spatial variation of plant species numbers in boreal forests.Manuscript (preprint) (Other academic)
  • 1265.
    Zinko, Ursula
    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.
    Nilsson, Christer
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Seibert, Jan
    Department of Physical Geography and Quaternary Geology, Stockholm University.
    The role of soil pH in linking groundwater flow and plant species density in boreal forest landscapes2006In: Ecography, ISSN 0906-7590, E-ISSN 1600-0587, Vol. 29, no 4, p. 515-524Article in journal (Refereed)
    Abstract [en]

    In hilly boreal landscapes topography governs groundwater flow which strongly influences soil development, and thus vegetation composition. Soil pH is known to correlate well with plant species density and composition, but in boreal forests this relationship has been little studied. Previously, we successfully used a topography-based hydrological index, the topographical wetness index (TWI), as an approximation of the variation in groundwater flow to predict local plant species density in a boreal forest landscape. Data on species indicator values demonstrated that soil pH can be an important soil variable linking groundwater flow and plant species density. In the present paper we explore this link by relating measured soil pH to species numbers of vascular plants and TWI in 200-m2 plots within two boreal forest landscapes, differing in average soil pH. The two landscapes showed almost identical relationships between plant species number and soil pH, implying that this relationship is robust. The landscapes also had similar relationships between soil pH and TWI as well as between plant species number and TWI except at high TWI values, which indicate groundwater discharge areas. In these areas soil pH and plant species numbers were higher in the high-pH landscape at any given TWI value. We conclude that for predictive mapping of the species density of vascular plants in boreal forests, soil pH is a major factor. However, TWI as a measure of groundwater flow is a practical alternative predictor.

  • 1266.
    Zinko, Ursula
    et al.
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Seibert, Jan
    Dynesius, Mats
    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.
    Plant species number predicted by a topography based groundwater-flow index2005In: Ecosystems (New York. Print), ISSN 1432-9840, E-ISSN 1435-0629, Vol. 8, no 4, p. 430-441Article in journal (Refereed)
    Abstract [en]

    The lack of a clear understanding of the factors governing the often-great variation of species numbers over entire landscapes confounds attempts to manage biodiversity. We hypothesized that in a topographically variable boreal forest landscape the availability of shallow groundwater is a major determinant of plant species numbers. We then developed a topographically derived hydrologic index based on multidirectional flow algorithms to account for the variation in availability of such groundwater in the landscape. We found a positive correlation between species numbers of vascular plants in plots ranging from 0.01 to 200 m2 and the hydrologic index. Generally, the landscape was relatively dry and species-poor, but interspersed patches with shallow groundwater had high species numbers and high proportions of regionally uncommon plant species. The index explained 30% of the variation in vascular plant number and correlated quite well (rs = 0.50) with groundwater level, but not as well with a community H+concentration value (instead of community pH, rs = −0.31), based on species composition. In addition, we found a very strong correlation between species number and the community H+ concentration value (rs−0.84). The hydrologic index is a useful tool for the identification of spatial of species number patterns across entire landscapes. This is an important step in identifying the areas most in need of protection or restoration, designing survey techniques, and understanding the fundamental processes that control the spatial distribution of species.

  • 1267.
    Åberg, Jan
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Production and emission of CO2 in two unproductive lakes in northern Sweden2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Unproductive lakes are one of few natural landscape compartments with net release of carbon to the atmosphere. Lakes also generally decrease the net terrestrial carbon uptake, since most of the CO2 production in unproductive lakes are derived from organic carbon produced on land (e.g. in forests). High latitude lakes are predicted to be particularly affected by the global climate change. The carbon cycling in these lakes and their role in the landscape are therefore important to study.

    In this thesis, carbon turnover processes were studied in two lakes above the arctic circle (Lake Diktar-Erik and Lake Merasjärvi) in year 2004 and 2005. Both lakes were net heterotrophic, with large variations in CO2 concentrations both on shorter (30min) and longer (24h) time-scales. The pelagic habitat supported a major part of the net production of CO2, with larger dynamics in the CO2 production than the sediments. The CO2 variations of the surface water were related to respiration of allochthonous organic carbon, and were affected by the concentration and quality of the DOC, as well as the whole lake water temperatures, and vertical water movements.

    The emission of CO2 from Lake Merasjärvi was measured with the eddy covariance tech­nique. The results showed that the gas transfer rate during moderate winds were higher than expected, causing the two most commonly used models to underestimate the long term fluxes of CO2 from the lake.

    Taken together, the results of the thesis show that the studied lakes contributed to bring terrestrial organic carbon back into the atmosphere, driven by a substantial internal CO2 production based on mineralization of allochthonous organic carbon. Major results are that the eddy covariance technique indicated that commonly used models tend to underestimate the net release rate of CO2 from lakes to the atmosphere, and that the lake CO2 dynamics can be the results of interactions between biogeochemical and physical processes in the lake water.

  • 1268.
    Åhlén, Emma
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Fingerprints of planktivory: paleolimnological evidence of past fish community structure and dynamics2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Planktivorous fish affect the species composition, size and morphology of their zooplankton prey by size selective predation. Remains of cladocerans are deposited in the lake sediments and this microfossil community hence reflects the historical changes in the planktivore fish community. Most earlier work on quantitatively inferring past planktivory deals with ephippia (resting eggs) of Daphnia, however these remains are very scarce in northern Swedish lakes. In these lakes, often dominated by fish that are not obligate planktivores, such as perch (Perca fluviatilis), the individual size to a large degree determines the type of resource consumed. Therefore, in these lakes, the size distribution as well as the density of the fish community determines the overall planktivoryThis thesis deals with evaluating the use of Bosmina remains in the sediment as indicators of past planktivory. I developed a transfer function based on Bosmina remains to be used in oligotrophic lakes with omnivorous species to reconstruct past planktivory. I test the transfer function in a lake where the history is to a large extent known. Furthermore, in this thesis a novel quantitative measure of planktivore pressure, the PCC (Planktivore Community Capacity) was developed. It was also possible to compare the morphology measurements of carapace length and mucro length of contemporary Bosmina sampled in the lake, with the same measurements on microfossils of Bosmina sedimented during the corresponding time period. By using the resurrection approach this thesis also evaluates the use of Ceriodaphnia clones as indicators of micro-evolutionary responses to past planktivory.From the studies in this thesis I can draw some major conclusions; the morphological measurements carapace length and mucro length of Bosmina can be used to infer past planktivory in northern Swedish lakes. PCC has a higher explanatory power than CPUE in these lakes dominated by omnivorous fish. The morphology of the contemporary Bosmina corresponds well with the remains found in the sediment dating from the same time period. Both the contemporary and microfossil Bosmina changes in body size characteristics was in turn strongly related to PPC. Finally, the hatching of Ceriodaphnia ephippia is promising for studying past planktivory, both because of the high viability of the ephippia and the relationship between eye area and inferred PCC.

  • 1269.
    Åkerlund, Elisabeth
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Why two sexes in separate individuals? The evolution of dioecy in plants.2009Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
  • 1270.
    Årdahl, Kerstin
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Reindeer in the archipelago of Holmöarna: Abundance of habitats and how reindeer have utilized them during winter 2015-16 and summer 20162017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the winter 2015/2016, about 700 reindeer were winter grazing on the islands of Holmöarna. Since the islands had not been used for reindeer grazing for more than 100 years, this is a unique opportunity to study how reindeer influence the vegetation that has developed in the absence of reindeer. Moreover, it also means that all reindeer faeces depositions and grazing damages originate from the last year. Most of the reindeer grazing occurred on Ängesön and Grossgrunden, at least during winter, due to lichen rich habitats. To investigate which habitats were available for reindeer, the abundance of these habitats and which resources they provide, 239 randomly selected study sites were investigated. To find out reindeer utilization of resources and impact on vegetation, all faecal droppings from reindeer were counted. Also, lichen height, lichen cover, lichen volume, grazing damages of lichens and vegetation, trampling, and digging, were recorded at every study site. Old-grown spruce forest was the most abundant habitat, providing reindeer with ground lichens, bilberries and epiphytic lichens. Pine forest, rich in ground lichens, was the most preferred and used habitat based on lichen cover and lichen volume, lichen damage and trampling. NMSD ordination confirmed a strong relationship between lichen height and lichen cover, i.e. lichens were heavily grazed in every habitat where lichens were recorded. Reindeer depositions of dungs and pellets were found in all habitats, but were most abundant in spruce forest with ground lichens. Strong relationships between lichen damages, digging signs and reindeer pellets confirmed more activities where lichens were abundant. Grazing of bilberry shoots and trampling, both indications of summer activities by reindeer, were also closely associated, indicating that bilberry shoots was an important food resource in summer on these islands. In the light of my result, the islands of Holmöarna have good provision for reindeer, in winter by richness of ground lichens in pine forest and old spruce forest, and summer primarily by bilberries in old grown spruce forest, mixed forest and pine forest with Vaccinium ssp. Although almost all suitable habitats show signs of reindeer activities after only one year, there is still abundant winter and summer food resources available for future grazing. There is thus plenty of resources available for reindeer on the islands of Holmöarna and reindeer are able to utilize them. If they are suitable to use for reindeer grazing in the future is thus more dependent on logistic problems like difficulties in transporting the reindeer from mainland to the islands.

  • 1271.
    Åslund, Daniel
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Toxicity of extracts from mercury contaminated sediments on the crustaceans Daphnia magna and Nitocra spinipes2006Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
  • 1272.
    Ögren, Amanda
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Is above- and belowground phenology of Eriophorum vaginatum in sync in a peatland underlain by permafrost?2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The phenology of plants in northern ecosystems is currently changing. Roots have a key role in these ecosystems, though the phenology of roots is still poorly understood. The aim of this report was to investigate if above- and belowground phenology of the circumpolar sedge Eriophorum vaginatum was synchronized in a subarctic peatland underlain by permafrost, and to investigate which abiotic factors are limiting root growth. Additionally, the length of the belowground growing season was examined. The study was performed with a non-destructive in situ method (minirhizotrons and NDVI measurements) in the northernmost part of Sweden. Both above- and belowground phenology was measured biweekly during the whole growing season in 2016. The depth of the active layer, air temperature, soil temperature and soil moisture were measured to investigate the determinants of root growth. Root growth and aboveground activity was asynchronous, as peak in root growth occurred on average 21 days before maximum NDVI was reached. Soil temperature and thaw depth seem to be important factors regulating root growth in this peatland. The result highlight that solely studying the aboveground parts of plants can give a misleading interpretation about the phenology of the entire plant and thus during which time periods important ecosystem processes take place. Hence, to more accurate forecast ecosystem responses to global warming, both aboveground and belowground phenology should be considered.

  • 1273.
    Öhlund, Gunnar
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Ecological and evolutionary effects of predation in environmental gradients2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Understanding species interactions and how they affect densities and distributions of organisms is a central theme in ecological research. Studying such interactions in an ecosystem context is challenging as they often depend on species-specific characteristics and rates that not only change during the ontogeny of an organism, but also are affected by the surrounding environment. This thesis focuses on two separate questions and study systems that highlight different aspects of how effects of predation can depend on environmental conditions. In the first part of the thesis, we studied how temperature affects attack rate and handling time, two ecological rates with profound importance for predator-prey dynamics. Using a metaanalysis, we first show that the currently dominating model for temperature dependence in predator-prey interactions, i.e. the Arrhenius equation, has weak support in available empirical literature. This suggests that we need new rules for how and when we can generalize on the temperature-dependence of intake rates. We then use a simple model and a series of experiments to demonstrate that differences in the relative physiological capacity between predator and prey can impose strong non-linear effects on temperature-response curves of attack rate. In the second part of the thesis, we study the role of predation along a benthic-pelagic habitat gradient in promoting divergence and resource polymorphism among prey. We show that presence of a large piscivorous predator, the northern pike (Esox lucius), induces dwarfs, giants or divergence into both ecotypes in populations of European whitefish (Coregonus lavaretus) depending on lake characteristics. Using dated introductions of whitefish as controlled natural experiments, we show that pike presence induces rapid life history divergence between pelagic and littoral habitat use strategies, and that this divergence can translate into partial reproductive isolation in a matter of decades. Our results demonstrate the potential for thresholds in a crucial ecological rate, setting the stage for tipping points with potentially far reaching implications for effects of warming on predator prey dynamics and ecosystem stability. Moreover, they illustrate the potentially drastic consequences of such tipping points by demonstrating the importance of a single predator species as a driving force behind the creation and maintenance of biodiversity in a natural system.  

  • 1274.
    Öhlund, Gunnar
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hedström, Per
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Norman, Sven
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Hein, Catherine L.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Englund, Göran
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Temperature-dependence of predation depends on relative performance of predators and preyManuscript (preprint) (Other academic)
  • 1275.
    Örnmark, Jannice
    Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
    Utvärdering och optimering av en biologisk fosforavskiljningsprocess vid Duvbackens reningsverk.Mikrobiologiska, processtekniska och externa aspekter2007Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
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