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  • 1.
    Altizer, Sonia
    et al.
    Institute of Ecology, University of Georgia.
    Nunn, Charles L
    Max Planck Institute for Evolutionary Anthropology, Department of Integrative Biology, University of California, Berkeley.
    Lindenfors, Patrik
    Stockholm University, Faculty of Science, Department of Zoology. Stockholm University, Faculty of Humanities, Centre for the Study of Cultural Evolution.
    Do threatened hosts have fewer parasites?: A comparative study in primates2007In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 76, p. 304-314Article in journal (Refereed)
    Abstract [en]

    1. Parasites and infectious diseases have become a major concern in conservation biology, in part because they can trigger or accelerate species or population declines. Focusing on primates as a well-studied host clade, we tested whether the species richness and prevalence of parasites differed between threatened and non-threatened host species.

    2. We collated data on 386 species of parasites (including viruses, bacteria, protozoa, helminths and arthropods) reported to infect wild populations of 36 threatened and 81 non-threatened primate species. Analyses controlled for uneven sampling effort and host phylogeny.

    3. Results showed that total parasite species richness was lower among threatened primates, supporting the prediction that small, isolated host populations harbour fewer parasite species. This trend was consistent across three major parasite groups found in primates (helminths, protozoa and viruses). Counter to our predictions, patterns of parasite species richness were independent of parasite transmission mode and the degree of host specificity.

    4. We also examined the prevalence of selected parasite genera among primate sister-taxa that differed in their ranked threat categories, but found no significant differences in prevalence between threatened and non-threatened hosts.

    5. This study is the first to demonstrate differences in parasite richness relative to host threat status. Results indicate that human activities and host characteristics that increase the extinction risk of wild animal species may lead simultaneously to the loss of parasites. Lower average parasite richness in threatened host taxa also points to the need for a better understanding of the cascading effects of host biodiversity loss for affiliated parasite species.

  • 2.
    Auffret, Alistair G.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. University of York, UK.
    Rico, Yessica
    Bullock, James M.
    Hooftman, Danny A. P.
    Pakeman, Robin J.
    Soons, Merel B.
    Suarez-Esteban, Alberto
    Traveset, Anna
    Wagner, Helene H.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Plant functional connectivity - integrating landscape structure and effective dispersal2017In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 105, no 6, p. 1648-1656Article, review/survey (Refereed)
    Abstract [en]

    1. Dispersal is essential for species to survive the threats of habitat destruction and climate change. Combining descriptions of dispersal ability with those of landscape structure, the concept of functional connectivity has been popular for understanding and predicting species' spatial responses to environmental change. 2. Following recent advances, the functional connectivity concept is now able to move beyond landscape structure to consider more explicitly how other external factors such as climate and resources affect species movement. We argue that these factors, in addition to a consideration of the complete dispersal process, are critical for an accurate understanding of functional connectivity for plant species in response to environmental change. 3. We use recent advances in dispersal, landscape and molecular ecology to describe how a range of external factors can influence effective dispersal in plant species, and how the resulting functional connectivity can be assessed. 4. Synthesis. We define plant functional connectivity as the effective dispersal of propagules or pollen among habitat patches in a landscape. Plant functional connectivity is determined by a combination of landscape structure, interactions between plant, environment and dispersal vectors, and the successful establishment of individuals. We hope that this consolidation of recent research will help focus future connectivity research and conservation.

  • 3. Burns, Jean H.
    et al.
    Blomberg, Simon P.
    Crone, Elizabeth E.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Knight, Tiffany M.
    Pichancourt, Jean-Baptiste
    Ramula, Satu
    Wardle, Glenda M.
    Buckley, Yvonne M.
    Empirical tests of life-history evolution theory using phylogenetic analysis of plant demography2010In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 98, no 2, p. 334-344Article in journal (Refereed)
    Abstract [en]

    1. A primary goal of evolutionary ecology is to understand factors selecting for the diversity of life histories. Life-history components, such as time-to-reproduction, adult survivorship and fecundity, might differ among species because of variation in direct and indirect benefits of these life histories in different environments or might have lower-than-expected variability because of phylogenetic constraints. Here, we present a phylogenetic examination of demography and life histories using a data base of 204 terrestrial plant species. 2. Overall, statistical models without phylogeny were preferred to models with phylogeny for vital rates and elasticities, suggesting that they lacked phylogenetic signal and are evolutionarily labile. However, the effect of phylogeny was significant in models including sensitivities, suggesting that sensitivities exhibit greater phylogenetic signal than vital rates or elasticities. 3. Species with a greater age at first reproduction had lower fecundity, consistent with a cost of delayed reproduction, but only in some habitats (e.g. grassland). We found no evidence for an indirect benefit of delayed reproduction via a decrease in variation in fecundity with age to first reproduction. 4. The greater sensitivity and lower variation in survival than in fecundity was consistent with buffering of more important vital rates, as others have also found. This suggests that studies of life-history evolution should include survival, rather than only fecundity, for the majority of species. 5. Synthesis. Demographic matrix models can provide informative tests of life-history theory because of their shared construction and outputs and their widespread use among plant ecologists. Our comparative analysis suggested that there is a cost of delayed reproduction and that more important vital rates exhibit lower variability. The absolute importance of vital rates to population growth rates (sensitivities) exhibited phylogenetic signal, suggesting that a thorough understanding of life-history evolution might require an understanding of the importance of vital rates, not just their means, and the role of phylogenetic history.

  • 4.
    Dahl, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Deyanova, Diana
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lyimo, Liberatus D.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences. University of Dodoma, Tanzania.
    Näslund, Johan
    Samuelsson, Göran S.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Mtolera, Marten S. P.
    Björk, Mats
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gullström, Martin
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Effects of shading and simulated grazing on carbon sequestration in a tropical seagrass meadow2016In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 104, no 3, p. 654-664Article in journal (Refereed)
    Abstract [en]

    1. There is an ongoing world-wide decline of seagrass ecosystems, one of the world's most efficient carbon sink habitats. In spite of this, there is a clear lack of studies experimentally testing the effects of anthropogenic disturbances on carbon sequestration of seagrass systems. 2. We assessed the effects of two disturbances of global concern on the carbon sink function in a five-month in situ experiment within a tropical seagrass (Thalassia hemprichii) meadow by testing the impacts of shading and simulated grazing at two levels of intensity using shading cloths and clipping of shoot tissue. We measured the effects of these disturbances on the carbon sequestration process by assessing the net community production (NCP), carbon and nitrogen content in tissue biomass, and organic matter and THAA (total hydrolysable amino acids) in the sediment down to 40 cm depth. 3. Treatments of high-intensity shading and high-intensity clipping were similarly impacted and showed a significantly lower NCP and carbon content in the below-ground biomass compared to the seagrass control. No significant effects were seen in organic carbon, total nitrogen, C:N ratio and THAA in the sediment for the seagrass treatments. However, both clipping treatments showed different depth profiles of carbon and THAA compared to the seagrass control, with lower organic carbon and THAA content in the surface sediment. This can be explained by the clipping of shoot tissue causing a less efficient trapping of allochthonous carbon and reduced input of shredded seagrass leaves to the detritus sediment layer. In the clipping plots, erosion of the surface sediment occurred, which was also most likely caused by the removal of above-ground plant biomass. 4. Synthesis. Our findings show that during the course of this experiment, there were no impacts on the sedimentary carbon while the high-intensity disturbances caused a clear depletion of carbon biomass and reduced the seagrass meadow's capacity to sequester carbon. From a long-term perspective, the observed effect on the carbon biomass pool in the high-intensity treatments and the sediment erosion in the clipping plots may lead to loss in sedimentary carbon.

  • 5.
    Dahlgren, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Linking environmental variation to population dynamics of a forest herb2009In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 97, no 4, p. 666-674Article in journal (Refereed)
    Abstract [en]

    . Although necessary for understanding and predicting population dynamics, abiotic and biotic interactions have only rarely been coupled to demography and population dynamics.

    2. We estimated effects of 11 environmental factors on survival, growth and fertility of the perennial herb Actaea spicata and incorporated significant factors into integral projection models to assess their effect on population dynamics.

    3. Statistical models suggested that high soil potassium concentration increased individual growth and that seed predation and, to a lesser extent, canopy cover reduced seed production.

    4. Demographic models showed that both soil potassium concentration and pre-dispersal seed predation could reverse population growth from positive to negative. The observed range of soil potassium concentration corresponded to growth rates (lambda) between 0.96 and 1.07, at mean observed seed predation intensity. At observed mean potassium concentration, growth rate ranged from 0.99 to 1.02 over observed seed predation intensities.

    5. Sensitivity of population growth rate to different vital rates strongly influenced the relative effects of the two factors. Elasticity analysis suggested that proportional changes in soil potassium concentration result in seven times larger effects on population growth rate than changes in seed predation.

    6. Synthesis. We conclude that relatively weak associations between environmental factors and vital rates can have substantial long-term effects on population growth. Approaches based on detailed demographic models, that simultaneously assess abiotic and biotic effects on population growth rate, constitute important tools for establishing the links between the environment and dynamics of populations and communities.

  • 6. De Frenne, Pieter
    et al.
    Baeten, Lander
    Graae, Bente J.
    Brunet, Jorg
    Wulf, Monika
    Orczewska, Anna
    Kolb, Annette
    Jansen, Ivy
    Jamoneau, Aurelien
    Jacquemyn, Hans
    Hermy, Martin
    Diekmann, Martin
    De Schrijver, An
    De Sanctis, Michele
    Decocq, Guillaume
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Verheyen, Kris
    Interregional variation in the floristic recovery of post-agricultural forests2011In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 99, no 2, p. 600-609Article in journal (Refereed)
    Abstract [en]

    1. Worldwide, the floristic composition of temperate forests bears the imprint of past land use for decades to centuries as forests regrow on agricultural land. Many species, however, display significant interregional variation in their ability to (re)colonize post-agricultural forests. This variation in colonization across regions and the underlying factors remain largely unexplored. 2. We compiled data on 90 species and 812 species x study combinations from 18 studies across Europe that determined species' distribution patterns in ancient (i.e. continuously forested since the first available land use maps) and post-agricultural forests. The recovery rate (RR) of species in each landscape was quantified as the log-response ratio of the percentage occurrence in post-agricultural over ancient forest and related to the species-specific life-history traits and local (soil characteristics and light availability) and regional factors (landscape properties as habitat availability, time available for colonization, and climate). 3. For the herb species, we demonstrate a strong (interactive) effect of species' life-history traits and forest habitat availability on the RR of post-agricultural forest. In graminoids, however, none of the investigated variables were significantly related to the RR. 4. The better colonizing species that mainly belonged to the short-lived herbs group showed the largest interregional variability. Their recovery significantly increased with the amount of forest habitat within the landscape, whereas, surprisingly, the time available for colonization, climate, soil characteristics and light availability had no effect. 5. Synthesis. By analysing 18 independent studies across Europe, we clearly showed for the first time on a continental scale that the recovery of short-lived forest herbs increased with the forest habitat availability in the landscape. Small perennial forest herbs, however, were generally unsuccessful in colonizing post-agricultural forest even in relatively densely forested landscapes. Hence, our results stress the need to avoid ancient forest clearance to preserve the typical woodland flora.

  • 7. De Frenne, Pieter
    et al.
    Brunet, Jörg
    Cougnon, Mathias
    Decocq, Guillaume
    Graae, Bente J.
    Hagenblad, Jenny
    Hermy, Martin
    Kolb, Annette
    Lemke, Isgard H.
    Ma, Shiyu
    Orczewska, Anna
    Plue, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Vranckx, Guy
    Wulf, Monika
    Verheyen, Kris
    Biological Flora of the British Isles: Milium effusum2017In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 105, no 3, p. 839-858Article in journal (Refereed)
    Abstract [en]

    1. This account presents information on all aspects of the biology of Milium effusum L. (Wood Millet) that are relevant to understanding its ecological characteristics and behaviour. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, history, and conservation.

    2. The grass Milium effusum is a common species of mature woodland in central and southern England, but is less common in the wetter parts of northern England, Wales, Scotland and Ireland. Worldwide, the species is native to many temperate, boreal, subarctic and subalpine parts of the northern hemisphere: from eastern North America across most of Europe (excluding Mediterranean climates) to the Ural Mountains and Black Sea, extending eastwards to the Himalaya, Korea and Japan.

    3. Wood Millet is a shade-tolerant, relatively tall grass (up to 1.8 m) producing up to 700 caryopses per individual. It is characteristic of temperate deciduous woodland, but can also occur in other woodland and forest types and even in scrub, alpine meadows, along railways and roads, and on rocks. In woods, it is one of the most conspicuous plants of the herb layer in the early summer after the disappearance of spring flowering species. While the species is generally considered an ancient woodland indicator in England and western Europe, it is also known to colonize secondary, post-agricultural forests relatively rapidly in other areas such as Denmark, southern Sweden and Poland.

    4. The species has a wide amplitude in terms of soil acidity and nutrient availability, but predominantly grows on soils of intermediate soil fertility and soil pH and with high organic matter concentration. However, M. effusum can tolerate large quantities of tree-leaf litter on the forest floor and is able to grow on very acidic soils.

    5. Changes in land use, climate, densities of large herbivores and atmospheric deposition of nitrogen are having effects on populations of Wood Millet. Significant responses of the life-history traits and population characteristics have been detected in response to environmental variation and to experimental treatments of temperature, nutrients, light and acidity. In many of its habitats across its range, M. effusum is currently becoming more frequent. During the last century, its mean elevation of occurrence in upland areas of Europe has also increased by several hundreds of metres. Typically, management actions are directed towards the conservation of its main habitat type (e.g. ancient woodlands of the Milio-Fagetum association) rather than to the species specifically.

  • 8. De Frenne, Pieter
    et al.
    Graae, Bente J.
    Rodriguez-Sanchez, Francisco
    Kolb, Annette
    Chabrerie, Olivier
    Decocq, Guillaume
    De Kort, Hanne
    De Schrijver, An
    Diekmann, Martin
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Gruwez, Robert
    Hermy, Martin
    Lenoir, Jonathan
    Plue, Jan
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Coomes, David A.
    Verheyen, Kris
    Latitudinal gradients as natural laboratories to infer species' responses to temperature2013In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 101, no 3, p. 784-795Article, review/survey (Refereed)
    Abstract [en]

    Macroclimatic variation along latitudinal gradients provides an excellent natural laboratory to investigate the role of temperature and the potential impacts of climate warming on terrestrial organisms. Here, we review the use of latitudinal gradients for ecological climate change research, in comparison with altitudinal gradients and experimental warming, and illustrate their use and caveats with a meta-analysis of latitudinal intraspecific variation in important life-history traits of vascular plants. We first provide an overview of latitudinal patterns in temperature and other abiotic and biotic environmental variables in terrestrial ecosystems. We then assess the latitudinal intraspecific variation present in five key life-history traits [plant height, specific leaf area (SLA), foliar nitrogen:phosphorus (N:P) stoichiometry, seed mass and root:shoot (R:S) ratio] in natural populations or common garden experiments across a total of 98 plant species. Intraspecific leaf N:P ratio and seed mass significantly decreased with latitude in natural populations. Conversely, the plant height decreased and SLA increased significantly with latitude of population origin in common garden experiments. However, less than a third of the investigated latitudinal transect studies also formally disentangled the effects of temperature from other environmental drivers which potentially hampers the translation from latitudinal effects into a temperature signal. Synthesis. Latitudinal gradients provide a methodological set-up to overcome the drawbacks of other observational and experimental warming methods. Our synthesis indicates that many life-history traits of plants vary with latitude but the translation of latitudinal clines into responses to temperature is a crucial step. Therefore, especially adaptive differentiation of populations and confounding environmental factors other than temperature need to be considered. More generally, integrated approaches of observational studies along temperature gradients, experimental methods and common garden experiments increasingly emerge as the way forward to further our understanding of species and community responses to climate warming.

  • 9.
    Ehrlén, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Morris, William F.
    von Euler, Tove
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Dahlgren, Johan P.
    Advancing environmentally explicit structured population models of plants2016In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 104, no 2, p. 292-305Article in journal (Refereed)
    Abstract [en]

    The relationship between the performance of individuals and the surrounding environment is fundamental in ecology and evolutionary biology. Assessing how abiotic and biotic environmental factors influence demographic processes is necessary to understand and predict population dynamics, as well as species distributions and abundances. We searched the literature for studies that have linked abiotic and biotic environmental factors to vital rates and, using structured demographic models, population growth rates of plants. We found 136 studies that had examined the environmental drivers of plant demography. The number of studies has been increasing rapidly in recent years. Based on the reviewed studies, we identify and discuss several major gaps in our knowledge of environmentally driven demography of plants. We argue that some drivers may have been underexplored and that the full potential of spatially and temporally replicated studies may not have been realized. We also stress the need to employ relevant statistical methods and experiments to correctly identify drivers. Moreover, assessments of the relationship between drivers and vital rates need to consider interactive, nonlinear and indirect effects, as well as effects of intraspecific density dependence.Synthesis. Much progress has already been made by using structured population models to link the performance of individuals to the surrounding environment. However, by improving the design and analyses of future studies, we can substantially increase our ability to predict changes in plant population dynamics, abundances and distributions in response to changes in specific environmental drivers. Future environmentally explicit demographic models should also address how genetic changes prompted by selection imposed by environmental changes will alter population trajectories in the face of continued environmental change and investigate the reciprocal feedback between plants and their biotic drivers.

  • 10.
    Fogelström, Elsa
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Phenotypic but not genotypic selection for earlier flowering in a perennial herb2019In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745Article in journal (Refereed)
    Abstract [en]

    1. Timing of reproduction affects the outcome of interactions between plants and their pollinators, grazers and seed predators, as well as with their local abiotic environment. In seasonal environments, phenotypic selection has often been shown to favour early flowering. Yet, we still know little about the agents driving selection in natural populations and whether observed phenotypic selection corresponds to genotypic selection – a prerequisite for evolutionary change.

    2. In this study, we experimentally assessed phenotypic and genotypic selection for flowering time in a natural population of the perennial herb Lathyrus vernus. We transplanted sibling individuals, obtained through controlled crosses, to their source population and found net phenotypic selection for earlier flowering in the field.

    3. Despite a higher susceptibility to roe deer grazing, early‐flowering plants had higher fruit set and more seeds per fruit than late‐flowering plants. We found no support for genotypic selection on flowering time, and heritability for first flowering day was very low.

    4. Synthesis: Our results suggest that commonly observed patterns of higher fitness in early‐flowering plants do not always correspond to selection on genotypic values and are thus not necessarily expected to result in evolutionary change even if the relationship between flowering time and fitness is causal. This finding should be important to understand how species phenology might respond to changing environmental conditions.

  • 11. Garcia, Maria B.
    et al.
    Dahlgren, Johan P.
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlen, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    No evidence of senescence in a 300-year-old mountain herb2011In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 99, no 6, p. 1424-1430Article in journal (Refereed)
    Abstract [en]

    1. Understanding how vital rates and reproductive value change with age is fundamental to demography, life history evolution and population genetics. The universality of organism senescence has been questioned on both theoretical and empirical grounds, and the prevalence and strength of senescence remain a controversial issue. Plants are particularly interesting for studies of senescence since individuals of many species have been reported to reach very high ages. 2. In this study, we examined whether the herb Borderea pyrenaica, known to reach ages of more than 300 years, experiences senescence. We collected detailed demographic information from male and female individuals in two populations over 5 years. An unusual morphological feature in this species enabled us to obtain exact age estimates for each of the individuals at the end of the demographic study. 3. We used restricted cubic regression splines and generalized linear models to determine nonlinear effects of age and size on vital rates. We then incorporated the effects of age and size in integral projection models of demography for determining the relationship between age and reproductive value. As the species is dioecious, we performed analyses separately for males and females and examined also the hypothesis that a larger reproductive effort in females comes at a senescence cost. 4. We found no evidence for senescence. Recorded individuals reached 260 years, but growth and fecundity of female and male individuals did not decrease at high ages, and survival and reproductive value increased with age. The results were qualitatively similar also when accounting for size and among-individual vital rate heterogeneity, with the exception that male flowering probability decreased with age when accounting for size increases. 5. Synthesis. Overall, our results show that performance of both male and female plants of B. pyrenaica may increase rather than decrease at ages up to several centuries, and they support the notion that senescence may be negligible in long-lived modular organisms. This highlights the need to explore mechanisms that enable some species to maintain high reproductive values also at very high ages and to identify the evolutionary reasons why some organisms appear to experience no or negligible senescence.

  • 12. Gustafsson, Camilla
    et al.
    Norkko, Alf
    Stockholm University, Faculty of Science, Stockholm University Baltic Sea Centre. University of Helsinki, Finland.
    Quantifying the importance of functional traits for primary production in aquatic plant communities2019In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 107, no 1, p. 154-166Article in journal (Refereed)
    Abstract [en]

    1. Aquatic plant meadows are important coastal habitats that sustain many ecosystem functions such as primary production and carbon sequestration. Currently, there is a knowledge gap in understanding which plant functional traits, for example, leaf size or plant height underlie primary production in aquatic plant communities.

    2. To study how plant traits are related to primary production, we conducted a field survey in the Baltic Sea, Finland, which is characterized by high plant species and functional diversity. Thirty sites along an exposure gradient were sampled (150 plots), and nine plant morphological and chemical traits measured. The aim was to discern how community-weighted mean traits affect community production and whether this relationship changes along an environmental gradient using structural equation modelling (SEM).

    3. Plant height had a direct positive effect on production along an exposure gradient (r=0.33) and indirect effects through two leaf chemical traits, leaf delta N-15 and leaf delta C-13 (r=0.24 and 0.18, respectively) resulting in a total effect of 0.28. In plant communities experiencing varying exposure, traits such as root N concentration and leaf delta N-15 had positive and negative effects on production, respectively.

    4. Synthesis. Our results demonstrate that the relationship between aquatic plant functional traits and community production is variable and changes over environmental gradients. Plant height generally has a positive effect on community production along an exposure gradient, while the link between other traits and production changes in plant communities experiencing varying degrees of exposure. Thus, the underlying biological mechanisms influencing production differ in plant communities, emphasizing the need to resolve variability and its drivers in real-world communities. Importantly, functionally diverse plant communities sustain ecosystem functioning differently and highlight the importance of benthic diversity for coastal ecosystem stability.

  • 13. Harper, Karen A.
    et al.
    Macdonald, S. Ellen
    Mayerhofer, Michael S.
    Biswas, Shekhar R.
    Esseen, Per-Anders
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Stewart, Katherine J.
    Mallik, Azim U.
    Drapeau, Pierre
    Jonsson, Bengt-Gunnar
    Lesieur, Daniel
    Kouki, Jari
    Bergeron, Yves
    Edge influence on vegetation at natural and anthropogenic edges of boreal forests in Canada and Fennoscandia2015In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 103, no 3, p. 550-562Article in journal (Refereed)
    Abstract [en]

    Although anthropogenic edges are an important consequence of timber harvesting, edges due to natural disturbances or landscape heterogeneity are also common. Forest edges have been well studied in temperate and tropical forests, but less so in less productive, disturbance-adapted boreal forests. We synthesized data on forest vegetation at edges of boreal forests and compared edge influence among edge types (fire, cut, lake/wetland; old vs. young), forest types (broadleaf vs. coniferous) and geographic regions. Our objectives were to quantify vegetation responses at edges of all types and to compare the strength and extent of edge influence among different types of edges and forests. Research was conducted using the same general sampling design in Alberta, Ontario and Quebec in Canada, and in Sweden and Finland. We conducted a meta-analysis for a variety of response variables including forest structure, deadwood abundance, regeneration, understorey abundance and diversity, and non-vascular plant cover. We also determined the magnitude and distance of edge influence (DEI) using randomization tests. Some edge responses (lower tree basal area, tree canopy and bryophyte cover; more logs; higher regeneration) were significant overall across studies. Edge influence on ground vegetation in boreal forests was generally weak, not very extensive (DEI usually <20m) and decreased with time. We found more extensive edge influence at natural edges, at younger edges and in broadleaf forests. The comparison among regions revealed weaker edge influence in Fennoscandian forests.Synthesis. Edges created by forest harvesting do not appear to have as strong, extensive or persistent influence on vegetation in boreal as in tropical or temperate forested ecosystems. We attribute this apparent resistance to shorter canopy heights, inherent heterogeneity in boreal forests and their adaptation to frequent natural disturbance. Nevertheless, notable differences between forest structure responses to natural (fire) and anthropogenic (cut) edges raise concerns about biodiversity implications of extensive creation of anthropogenic edges. By highlighting universal responses to edge influence in boreal forests that are significant irrespective of edge or forest type, and those which vary by edge type, we provide a context for the conservation of boreal forests.

  • 14. Herben, T
    et al.
    Münzbergová, Z
    Mildén, Mikael
    Stockholm University, Faculty of Science, Department of Botany.
    Ehrlén, Johan
    Cousins, Sara A O
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    Longterm spatial dynamics of Succisa pratensis in a changing rural landscape: linking dynamical modelling with historical maps2006In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 94, no 1, p. 131-143Article in journal (Refereed)
    Abstract [en]

    We attempt to explain the current distribution of a long-lived perennial plant, Succisa pratensis, in a rural landscape in southern Sweden by linking its population biology with documented changes in the landscape, using a dynamical, spatially explicit model incorporating population dynamics and spatial spreading of the plant. Changes in the landscape were inferred from historical maps (1850 and 1900) and aerial photographs (1945 and 2001).

     

    We tested whether predictions for the current species distribution are affected by assumptions about its early 19th century distribution, to determine whether recent history and current processes are dominant, and how past landscape changes determine current distributions.

     

    Initial conditions influence predictions of current distribution, suggesting that the current distribution still partly reflects the distribution of the species in the early 19th century. A period of 150 years is too short for Succisa to have spread extensively if dispersal parameters are given realistic values.

     

    Simulations in which present-day land-use patterns were imposed at earlier dates showed that changes in landscape structure over the past 175 years also had a strong effect on the present-day habitat occupancy and population sizes of Succisa.

     

    The dominant process for Succisanow is extinction from marginal habitats. It is therefore likely that the (relatively) high present-day occupation patterns are still due to much larger areas having been available in the past rather than to successful dispersal. Although the species has responded to landscape changes, there is little evidence of population sizes reaching equilibrium.

     

    Our approach shows that the wealth of landscape information available from historical maps can be linked with data on population biology by means of dynamical models that can make predictions about species dynamics.

  • 15. Horvitz, Carol C.
    et al.
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Matlaga, David
    Context-dependent pollinator limitation in stochastic environments: can increased seed set overpower the cost of reproduction in an understorey herb?2010In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 98, no 2, p. 268-278Article in journal (Refereed)
    Abstract [en]

    1. In the understorey herb Lathyrus vernus seed production is pollen limited, but increased reproduction results in a lower probability of remaining reproductive. Putting these two results together, previous research reported that population growth rate lambda was negatively impacted by high pollination. 2. Thus, costs and benefits have to be translated into the common currency of their respective effects on population dynamics to determine whether populations are truly pollen limited or whether they are already at an optimal level of pollination. 3. Also, when pollinators and demography vary from year to year we require a framework that examines reproductive benefits and demographic costs in the context of a variable environment. Whether or not additional pollination will increase the stochastic population growth rate lambda(S) depends upon the balance of stochastic elasticities of the costs and benefits. 4. In constant environment models, where seed survival, germination and seedling survival were increased, we found that the high cost of reproduction could be offset by improvements in seed survival and germination, but not by improvements of seedling survival. 5. In variable environment models, where changes in the sequence and frequencies of high- and low-pollination years mixed with occasional high-germination years were modelled, we found that increasing the frequency of high-germination conditions could offset the cost of reproduction, and the offset was even greater if high-germination years occurred after a high-pollination year or if high pollination was accompanied by high-germination conditions in the same year. 6. Both deterministic lambda and stochastic lambda(S) were less sensitive to perturbation of reproduction than to perturbation of the probability for flowering plants to remain reproductive. In other words, a small change in the parameter which is related to the 'cost' of reproduction had a bigger effect than a small change in the parameter which is related to the 'benefit' of increased pollination for Lathyrus. 7.Synthesis. Stochastic environment-specific elasticities for reproduction and stasis of flowering plants differ in their response to environmental context. The cost-benefit relationships, the ultimate fitness consequences of supplemental pollen, are influenced by the frequency and sequence of years differing in pollen availability and recruitment conditions.

  • 16.
    Johansson, Victor
    et al.
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Lönnell, Niklas
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Sundberg, Sebastian
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Release thresholds for moss spores: the importance of turbulence and sporophyte length2014In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 102, no 3, p. 721-729Article in journal (Refereed)
    Abstract [en]

    Adequately describing the dispersal mechanisms of a species is important for understanding and predicting its distribution dynamics in space and time. For wind-dispersed species, the transportation of airborne propagules is comparatively well studied, while the mechanisms triggering propagule release are poorly understood, especially for cryptogams. We investigated the effect of wind speed and turbulence on spore release in the moss Atrichum undulatum in a wind tunnel. Specifically, we measured the amount of spores released from sporophytes when exposed to different wind speeds, in high and low turbulence, using a particle counter. We also related spore release to variation in vibrations of the sporophyte and investigated how the vibrations were affected by wind speed, turbulence and sporophyte length (here including capsule, seta and the top part of the shoot). We show that in high turbulence, the amount of spores released increased with increasing wind speed, while in low turbulence, it did not, within the wind speed range 0.8-4.3ms(-1). However, there was a threshold in wind speed (similar to 2.5-3ms(-1)) before large amounts of spores started to be released in turbulent flow, which coincided with incipient vibrations of the sporophyte. Thresholds in wind variation, rather than average wind speed, seemed to initiate sporophyte vibrations. The vibration threshold increased with decreasing sporophyte length. The deposition of spores near the source decreased with increasing wind variation during the time of their release, based on simulated spore deposition from another study of moss dispersal. Synthesis. We suggest that vibration of moss sporophytes is an important mechanism to regulate spore release and that turbulence and sporophyte length regulate the onset of sporophyte vibration. Spore release thresholds affect dispersal distances and have implications for our understanding and predictions of species distribution patterns, population dynamics and persistence. The mechanisms of this phase of the dispersal process are also important to explore for other species, as there may be a substantial variation depending on the species' different traits.

  • 17. Jongejans, Eelke
    et al.
    Jorritsma-Wienk, Linda D.
    Becker, Ute
    Dostal, Petr
    Mildén, Mikael
    Stockholm University, Faculty of Science, Department of Botany.
    de Kroon, Hans
    Region versus site variation in the population dynamics of three short-lived perennials2010In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 98, no 2, p. 279-289Article in journal (Refereed)
    Abstract [en]

    1. When range shifts or invasions of plant species are studied, it is important to know whether large-scale spatial variation in a species' demography can be ignored or approximated by variation observed over smaller spatial scales. 2. Here, we studied the population dynamics of three similar (as shown by elasticity analysis) short-lived perennial plant species in multiple sites in different European countries over 2 years. We constructed a total of 40 transition matrices and analysed the spatio-temporal variation in the projected population growth rate (lambda) with spatially nested life table response experiments (LTRE). 3. All species (Carlina vulgaris, Tragopogon pratensis and Hypochaeris radicata) showed considerable life-history variation among regions on top of variation among sites within regions. 4. Net variance contributions (NVC), a novel LTRE statistic, revealed that in each species, variation in one group of vital rates contributed most to variation in lambda among regions as well as among sites. However, that most important type of vital rates differed between species: plant growth in C. vulgaris, flower head production in T. pratensis and establishment probability of seedlings in H. radicata. The rankings of the NVCs of other vital rates varied between site and region effects, suggesting that buffering through negative vital rate correlations varies over different spatial scales, while the identity of the main contributor to lambda variation is more constant. 5. Temporal effects were smaller than spatial effects, but the LTREs showed strong interactions between time and space (region or site), suggesting that the effect of, e.g. climate fluctuations are not synchronized throughout the distribution of a species. 6. Synthesis. This study shows that the life histories of plant species are distinguishable even when mean elasticity values show only small differences, and that life histories vary over the distribution range of a species. Demographic differences over large spatial scales can therefore only be partly substituted by small scale spatial variation in modelling studies on the population dynamics of a species across its entire distribution.

  • 18.
    Mazziotta, Adriano
    et al.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Granath, Gustaf
    Rydin, Håkan
    Bengtsson, Fia
    Norberg, Jon
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Scaling functional traits to ecosystem processes: Towards a mechanistic understanding in peat mosses2019In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 107, no 2, p. 843-859Article in journal (Refereed)
    Abstract [en]

    The role of trait trade-offs and environmental filtering in explaining the variability in functional traits and ecosystem processes has received considerable attention for vascular plants but less so for bryophytes. Thus, we do not know whether the same forces also shape the phenotypic variability of bryophytes. Here, we assess how environmental gradients and trade-offs shape functional traits and subsequently ecosystem processes for peat mosses (Sphagnum), a globally important plant genus for carbon accumulation. We used piecewise Structural Equation Modeling (SEM) to understand how environmental gradients influence vital processes across levels of biological organization. We gathered data on functional traits for 15 globally important Sphagnum species covering a wide range of ecological preferences. Phenotypes lie along well-established axes of the plant economic spectrum characterizing trade-offs between vital physiological functions. Using SEM, we clarified the mechanisms of trait covariation and scaling to ecosystem processes. We tested whether peat mosses, like vascular plants, constrain trait variability between a fast turnover strategy based on resource acquisition via fast traits and processes, and a strategy of resource conservation, via slow traits and processes. We parameterized a process-based model estimating ecosystem processes linking environmental drivers with architectural and functional traits. In our SEM approach the amount of variance explained varied substantially (0.29 <= R-2 <= 0.82) among traits and processes in Sphagnum, and the model could predict some of them with high to intermediate accuracy for an independent dataset. R-2 variability was mainly explained by traits and species identity, and poorly by environmental filtering. Some Sphagnum species avoid the stress caused by periodic desiccation in hollows via resource acquisition based on fast photosynthesis and growth, while other species are adapted to grow high above the water-table on hummocks by slow physiological traits and processes to conserve resources. Synthesis.We contribute to a unified theory generating individual fitness, canopy dynamics and ecosystem processes from trait variation. As for vascular plants, the functional traits in the Sphagnum economic spectrum are linked into an integrated phenotypic network partly filtered by the environment and shaped by trade-offs in resource acquisition and conservation.

  • 19.
    Moor, Helen
    et al.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Rydin, Håkan
    Hylander, Kristoffer
    Stockholm University, Faculty of Science, Department of Ecology, Environment and Plant Sciences.
    Nilsson, Mats B.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Norberg, Jon
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Towards a trait-based ecology of wetland vegetation2017In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 105, no 6, p. 1623-1635Article, review/survey (Refereed)
    Abstract [en]

    1. Functional traits mechanistically capture plant responses to environmental gradients as well as plant effects on ecosystem functioning. Yet most trait-based theory stems from terrestrial systems and extension to other habitats can provide new insights. 2. Wetlands differ from terrestrial systems in conditions (e.g. soil water saturation, anoxia, pH extremes), plant adaptations (e.g. aerenchyma, clonality, ubiquity of bryophytes) and important processes (e.g. denitrification, peat accumulation, methane emission). Wetland plant adaptations and trait (co-)variation can be situated along major plant trait trade-off axes (e.g. the resource economics spectrum), but soil saturation represents a complex stress gradient beyond a simple extension of commonly studied water availability gradients. 3. Traits that affect ecosystem functioning overlap with patterns in terrestrial systems. But wetland-specific traits that mediate plant effects on soil redox conditions, microbial communities and on water flow, as well as trait spectra of mosses, vary among wetland types. 4. Synthesis. With increasing availability of quantitative plant traits a trait-based ecology of wetlands is emerging, with the potential to advance process-based understanding and prediction. We provide an interactive cause-and-effect framework that may guide research efforts to disentangle the multiple interacting processes involved in scaling from environmental conditions to ecosystem functioning via plant communities.

  • 20. Nicole, Florence
    et al.
    Dahlgren, Johan P.
    Stockholm University, Faculty of Science, Department of Botany.
    Vivat, Agnes
    Till-Bottraud, Irene
    Ehrlén, Johan
    Stockholm University, Faculty of Science, Department of Botany.
    Interdependent effects of habitat quality and climate on population growth of an endangered plant2011In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 99, no 5, p. 1211-1218Article in journal (Refereed)
    Abstract [en]

    1. To predict the viability of populations, it is essential to clarify how performance depends both on large-scale environmental changes, such as climate warming, and on the local habitat. However, in spite of their potential importance, effects of interactions between large-scale environmental changes and the local environment on population viability have rarely been examined. 2. We investigated how population dynamics of the endangered alpine plant Dracocephalum austriacum depend on local habitat quality and climatic variation, as well as how effects of climate depend on local habitat. We used lasso regression shrinkage and integral projection models to identify effects on vital rates and population growth rates in seven populations over seven annual transitions. 3. Populations on steeper slopes had lower survival and stochastic population growth rate than populations on more gentle slopes. In years with low spring temperatures and high summer temperatures, survival and population growth rate were lower. In addition, the negative effects of high summer temperatures did depend on local habitat quality, being more negative in populations on steeper slopes. 4. Combining the net positive effects of high spring temperature and the net negative effects of high summer temperature on plant vital rates with predicted climate change over the next 30 years suggested that effects on D. austriacum would be relatively small. 5. Synthesis. Our results show that different aspects of a warmer climate may have opposing effects on populations, and that climatic effects may depend on local habitat quality. Such interactive effects should be accounted for when determining effects of large-scale environmental changes on population and community dynamics.

  • 21.
    Piqueras, Jesús
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education.
    Herbivory and ramet performance in the clonal herb Trientalis europaea L.1999In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 87, no 3, p. 450-460Article in journal (Refereed)
    Abstract [en]

    1 The intensity of leaf damage caused by invertebrate herbivores and grazing by vertebrates and their effects on clonal growth, survival and reproduction were examined in a population of the forest herb Trientalis europaea during 4 years.

    2 Levels of herbivory were low and varied between years in the studied population. Larger ramets were exposed to a greater risk of both grazing and leaf defoliation. Ramets that suffered leaf damage in 1 year experienced an increased probability of leaf damage in succeeding years. The probability of suffering herbivore attack was independent among the ramets belonging to the same clonal fragment, suggesting that clonal propagation might operate as a risk-spreading strategy in this species.

    3 Leaf damage did not affect any measure of plant performance, probably due to the low amounts of leaf area removed by invertebrate herbivores. In contrast, vertebrate grazing affected all phases of the pseudo-annual life cycle of T. europaea. Grazing prevented flowering and fruiting, increased ramet mortality during summer and decreased tuber production. Furthermore, grazed ramets produced shorter stolons and smaller tubers, which in turn had a lower winter survival and produced smaller ramets in the following growing season. The large impact of grazing was due to the consumption of the whole of the single shoot of ramets of T. europaea. Although regrowth was possible, secondary shoots were significantly smaller and assimilation was delayed.

    4 Tubers originating from grazed ramets were placed shallower than tubers from ungrazed ramets. This could be due to an alteration in the growth pattern of stolons of the grazed ramets.

  • 22.
    Piqueras, Jesús
    Stockholm University, Faculty of Science, Department of Mathematics and Science Education.
    Infection of Trientalis europaea by the systemic smut fungus Urocystis trientalis: disease incidence, transmission and effects on performance of host ramets1999In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 87, no 6, p. 995-1004Article in journal (Refereed)
    Abstract [en]

    1 The effects of fungus infection on a natural population of the pseudoannual plant Trientalis europaea were followed for 4 years.

    2 The incidence of the disease was low, showed little temporal variation during the period of study and was not affected by ramet size. Disease reduced flowering, fruiting, stolon length and the number and size of daughter tubers, all of which were positively correlated with ramet size. The year–disease interaction was not significant, except for flowering, suggesting little variation in the aggressiveness of the pathogen.

    3 Disease reduced survival of ramets to the end of the growing season, although the effect varied with ramet size, and decreased tuber survival both by reduction of tuber size and by reduction of the overwintering ability of tubers of a given size.

    4 For two of the three annual transitions the size of the offspring ramets was affected negatively by infection in the previous year.

    5 Disease transmission occurred along the stolons of only 31% of the diseased ramets. The probability of disease being shown in the following year decreased with stolon length.

    6 Although disease had a detrimental effect on ramet fitness, the low level of incidence and the stability of the clone dynamics in simulation models suggest only a minor role of the disease in population regulation in this species.

  • 23.
    Schmucki, Reto
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Reimark, Josefin
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lindborg, Regina
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Cousins, Sara A. O.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Landscape context and management regime structure plant diversity in grassland communities2012In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 100, no 5, p. 1164-1173Article in journal (Refereed)
    Abstract [en]

    1. Theoretical models show that environmental heterogeneity and dispersal are major determinants of species diversity at multiple scales, yet there are few studies from real landscapes that adequately integrate variation in the surrounding matrix. Understanding how landscape context and management influence species composition and diversity patterns across habitats and scales is an important goal in ecology with relevance for both management and conservation. 2. We used a system of 25 landscapes distributed across islands in the Baltic Sea to investigate the effect of current and historical landscape context and management on plant diversity and composition in grassland communities. Plant diversity was measured at three hierarchical scales (1 m2, habitat, landscape) in grazed fields and adjacent wood pastures to calculate a-, beta- and ?-diversity values across habitats and scales. 3. Structural equation modelling was used to model and quantify the effects of landscape context on species diversity and spatial turnover, and constraint analysis of principal coordinates to relate variation in species composition to landscape variables. 4. Proportion of open land, spacing and grazing intensity positively affected species diversity in both habitats, whereas the effect of historical landscape context was only significant in open fields. Plant diversity in field pastures was mainly determined by the number of species found at a small scale, while both local species density and spatial turnover were key determinants of diversity in wood pastures. 5. Habitat proximity influenced species composition as compositional similarity was higher between adjacent field and wood pastures compared to randomly paired habitats. Although increasing flow of propagules from adjacent patches can promote local coexistence, dispersal can result in spatial homogenization. 6. Synthesis. Plant diversity in grassland communities is substantially influenced by species occurring in adjacent habitats. While the effect of landscape context and management on small-scale diversity was consistent across habitats, the effect on spatial turnover was habitat specific. Our study shows that plant diversity is structured through the interplay between local and landscape processes and highlights that plant communities in specific habitat types cannot be considered in isolation from the surrounding landscape matrix.

  • 24. Verheyen, Kris
    et al.
    Baeten, Lander
    De Frenne, Pieter
    Bernhardt-Roemermann, Markus
    Brunet, Jorg
    Cornelis, Johnny
    Decocq, Guillaume
    Dierschke, Hartmut
    Eriksson, Ove
    Stockholm University, Faculty of Science, Department of Botany.
    Hedl, Radim
    Heinken, Thilo
    Hermy, Martin
    Hommel, Patrick
    Kirby, Keith
    Naaf, Tobias
    Peterken, George
    Petrik, Petr
    Pfadenhauer, Joerg
    Van Calster, Hans
    Walther, Gian-Reto
    Wulf, Monika
    Verstraeten, Gorik
    Driving factors behind the eutrophication signal in understorey plant communities of deciduous temperate forests2012In: Journal of Ecology, ISSN 0022-0477, E-ISSN 1365-2745, Vol. 100, no 2, p. 352-365Article in journal (Refereed)
    Abstract [en]

    1. Atmospheric nitrogen (N) deposition is expected to change forest understorey plant community composition and diversity, but results of experimental addition studies and observational studies are not yet conclusive. A shortcoming of observational studies, which are generally based on resurveys or sampling along large deposition gradients, is the occurrence of temporal or spatial confounding factors.

    2. We were able to assess the contribution of N deposition versus other ecological drivers on forest understorey plant communities by combining a temporal and spatial approach. Data from 1205 (semi-)permanent vegetation plots taken from 23 rigorously selected understorey resurvey studies along a large deposition gradient across deciduous temperate forest in Europe were compiled and related to various local and regional driving factors, including the rate of atmospheric N deposition, the change in large herbivore densities and the change in canopy cover and composition.

    3. Although no directional change in species richness occurred, there was considerable floristic turnover in the understorey plant community and a shift in species composition towards more shade-tolerant and nutrient-demanding species. However, atmospheric N deposition was not important in explaining the observed eutrophication signal. This signal seemed mainly related to a shift towards a denser canopy cover and a changed canopy species composition with a higher share of species with more easily decomposed litter.

    4. Synthesis. Our multi-site approach clearly demonstrates that one should be cautious when drawing conclusions about the impact of atmospheric N deposition based on the interpretation of plant community shifts in single sites or regions due to other, concurrent, ecological changes. Even though the effects of chronically increased N deposition on the forest plant communities are apparently obscured by the effects of canopy changes, the accumulated N might still have a significant impact. However, more research is needed to assess whether this N time bomb will indeed explode when canopies will open up again.

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