Christer Nilsson - Profile on Academia.edu (original) (raw)

Papers by Christer Nilsson

Journal of Applied Ecology, 2016

Summary Understanding and predicting ecosystem responses to multiple environmental pressures is a... more Summary 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. 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 poten...

Ecology and evolution, 2016

Environmental fluctuations exert strong control on behavior, survival, and fitness of stream biot... more Environmental fluctuations exert strong control on behavior, survival, and fitness of stream biota. Technical improvements increasingly allow for tracking the response of large numbers of individuals to environmental fluctuations, for instance, by remote detection of animals equipped with PIT (passive integrated transponder) tags. PIT tags were implanted into 393 juvenile and adult brown trout Salmo trutta L. and European sculpin Cottus gobio L. in a boreal stream subjected to considerable ice formation. With weekly trackings over 6 months, we quantified apparent survival and detection probability in relation to biological, environmental, and methodological factors. Individuals with a higher physical condition in autumn showed a higher apparent survival; this pattern was consistent across all species and age classes. Detection probability decreased with increasing thickness of the surface ice layer; this effect was most pronounced for juvenile trout and benthic-living sculpin, both ...

Vegetatio, 1983

Regulated shores 26, Unregulated shores 26 4.2 Substrate classification and analysis 4.3 Vegetati... more Regulated shores 26, Unregulated shores 26 4.2 Substrate classification and analysis 4.3 Vegetational analysis Layers 27, Cover (C) 27, Number of individuals or shoots (N) 28, Number of species (n5) 28, Difference and changeability quotients 28 4.4 Determination of buried seed content, seed production and seed weight 5 Vegetation dy namics 5.1 A strongly-exposed shore 5.2 Moderately-exposed shores 31 5.3 Weakly-exposed shores 5.4 A sheltered shore 5.5 The vegetational development at Site 5 in 1980 6 Site habitats and dy namics of vegetation 6. 1 Degree of exposure 6.2 Substrate type 42 Shore-level 42, Different substrates 45 6.3 Water-level fluctuations Sites 1-5 4 7, Site 6 50, Discussion 50 7 Survival strategies of the most fr equent sp ecies 7. 1 Selection of species 7.2 Bryophytes Bryophyte dynamics 53, Bryophyte survival strategies 53 7.3 Vascular plants Survival strategies of vascular plants 54, Discussion 62 53 53 53 Acta Phytogeogr. Suec. tions in (I) degree of exposure, (2) substrate type and (3) seasonal water-levels. Factors (I) and (2) were important for vegetational distribution while factor (3) chiefly governed the cyclic variations in plant cover, the richness in vascular plant species being related to between-year changes in the artificial fluctuations in water-level. Survival strategies of some common bryophytes and phanerogams, most of the latter weeds, are discussed with reference to During (1979). Most turned out to be annual shuttle strategists, fit for habitat conditions existing only for short periods.

$Research paper thumbnail of Remote estimation of the fraction of absorbed photosynthetically active radiation for a maize canopy in Northeast China$

Journal of Plant Ecology, 2014

Aims accurate remote estimation of the fraction of absorbed photosynthetically active radiation (... more 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 × (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.

Hydrological Processes, 2011

Evapotranspiration (ET), which links water, energy and the carbon cycle in terrestrial ecosystems... more 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 (Kc) 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 Kc 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 Kc values was mainly affected by SWC10cm and Rn, and the regression coefficients (R2) were 58·9 and 69·5%, respectively. These results will aid in making accurate and quantitative assessments of the vulnerability of the sparse...

Scots Pine (pinus sylvestris L.) on Shingle Fields: A Dendrochronologic Reconstruction of Early Summer Precipitation in Mideast Sweden

Journal of Climate, 2009

Scots pine (Pinus sylvestris L.) trees growing on shingle fields offer a unique possibility to re... more Scots pine (Pinus sylvestris L.) trees growing on shingle fields offer a unique possibility to reconstruct precipitation and study climate variability in the fairly humid eastern part of central Sweden. Tree-ring characteristics were compared with monthly (1890–2001) and daily (1961–2001) climate data from an adjacent meteorological station. Chronologies for latewood (LW), earlywood (EW), and tree-ring widths (RW) were constructed from 73 living and dead trees. Correlation analyses show that tree growth is most sensitive to early summer precipitation. EW shows the strongest correlation with precipitation in May and June while LW is best correlated with June and July precipitation. A reconstruction model for May–June precipitation was calculated using principal component analysis (PCA) regression (regular regression) including EW, LW, and RW for present and previous years. The model explained 46% of the variation in May–June precipitation and allowed a reconstruction back to 1560. In...

Ny lag behövs för att skydda åar och älvar

Vi vet idag mycket mer om de skadliga effekterna av dammar och flodesreglering, an vad som var ka... more Vi vet idag mycket mer om de skadliga effekterna av dammar och flodesreglering, an vad som var kant da vattenkraften byggdes ut i Sverige. I en ny utredning foreslas ocksa flera viktiga atgarder da ...

Water, 2020

The computational tool InSTHAn (indicators of short-term hydrological alteration) was developed t... more The computational tool InSTHAn (indicators of short-term hydrological alteration) was developed to summarize data on subdaily stream flows or water levels into manageable, comprehensive and ecologically meaningful metrics, and to qualify and quantify their deviation from unaltered states. The pronunciation of the acronym refers to the recording interval of input data (i.e., instant). We compared InSTHAn with the tool COSH-Tool in a characterization of the subdaily flow variability of the Colorado River downstream from the Glen Canyon dam, and in an evaluation of the effects of the dam on this variability. Both tools captured the hydropeaking caused by a dam operation, but only InSTHAn quantified the alteration of key flow attributes, highlighting significant increases in the range of within-day flow variations and in their rates of change. This information is vital to evaluate the potential ecological consequences of the hydrological alteration, and whether they may be irreversible,...

BioScience, 2018

Many streams and rivers experience major floods. Historically, human societies have responded to ... more 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.

Water, 2018

Many stream restoration projects aim to increase geomorphic complexity, assuming that this increa... more 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), whi...

Biological reviews of the Cambridge Philosophical Society, Jan 17, 2017

Hydropeaking refers to frequent, rapid and short-term fluctuations in water flow and water levels... more 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, reservo...

Ecological Applications, 2017

Recent research predicts that future climate change will result in substantial biodiversity loss ... more 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.

Ecosystems, 2016

Restoration of channelized streams by returning coarse sediment from stream edges to the wetted c... more Restoration of channelized streams by returning coarse sediment from stream edges to the wetted channel has become a common practice in Sweden. Yet, restoration activities do not always result in the return of desired biota. This study evaluated a restoration project in the Vindel River in northern Sweden in which practitioners further increased channel complexity of previously restored stream reaches by placing very large boulders (>1 m), trees (>8 m), and salmonid spawning gravel from adjacent upland areas into the channels. One reach restored with basic methods and another with enhanced methods were selected in each of ten different tributaries to the main channel. Geomorphic and hydraulic complexity was enhanced but the chemical composition of riparian soils and the communities of riparian plants and fish did not exhibit any clear responses to the enhanced restoration measures during the first 5 years compared to reaches restored with basic restoration methods. The variation in the collected data was among streams instead of between types of restored reaches. We conclude that restoration is a disturbance in itself, that immigration potential varies across landscapes, and that biotic recovery processes in boreal river systems are slow. We suggest that enhanced restoration has to apply a catchment-scale approach accounting for connectivity and availability of source populations, and that low-intensity monitoring has to be performed over several decades to evaluate restoration outcomes.

Logging residues and forest edges affect bryophyte vitality and growth in boreal forest clear-cuts

High resilience in stream-side bryophyte assemblages in boreal forests

Ecology, 2009

Restaurering av vattendrag i ett landskapsperspektiv : – en syntes av ”Second international Symposium on Riverine Landscapes”

Restaurering av vattendrag i ett landskapsperspektiv : – en syntes av ”Second international Sympo... more Restaurering av vattendrag i ett landskapsperspektiv : – en syntes av ”Second international Symposium on Riverine Landscapes”

Longitudinal variation in vegetation responses to disturbance in a riparian corridor along a boreal river

Longitudinal variation in vegetation responses to disturbance in a riparian corridor along a bore... more Longitudinal variation in vegetation responses to disturbance in a riparian corridor along a boreal river

Lie low : substrate form determines the fate of bryophytes in riparian buffer strips