Northern forest ecosystems are exposed to a range of anthropogenic processes including global warming, atmospheric deposition, and changing land‐use. The vegetation of northern forests is composed of ...species with several functional traits related to these processes, whose effects may be difficult to disentangle. Here, we combined analyses of spatio‐temporal dynamics and functional traits of ground flora species, including morphological characteristics, responses to macro‐ and microclimate, soil conditions, and disturbance. Based on data from the Swedish National Forest Inventory, we compared changes in occurrence of a large number of ground flora species during a 20‐year period (1994–2013) in boreal and temperate Sweden respectively. Our results show that a majority of the common ground flora species have changed their overall frequency. Comparisons of functional traits between increasing and declining species, and of trends in mean trait values of sample plots, indicate that current floristic changes are caused by combined effects of climate warming, nitrogen deposition and changing land‐use. Changes and their relations with plant traits were generally larger in temperate southern Sweden. Nutrient‐demanding species with mesotrophic morphology were favored by ongoing eutrophication due to nitrogen deposition in the temperate zone, while dwarf shrubs with low demands on nitrogen decreased in frequency. An increase of species with less northern and less eastern distribution limits was also restricted to temperate Sweden, and indicates effects of a moister and milder macroclimate. A trend toward dense plantation forests is mirrored by a decrease of light‐demanding species in both vegetation zones, and a decrease of grassland species in the temperate zone. Although denser tree canopies may buffer effects of a warmer climate and of nitrogen deposition to some extent, traits related to these processes were weakly correlated in the group of species with changing frequency. Hence, our results indicate specific effects of these often confounded anthropogenic processes.
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Summary
Forests harbour large spatiotemporal heterogeneity in canopy structure. This variation drives the microclimate and light availability at the forest floor. So far, we do not know how light ...availability and sub‐canopy temperature interactively mediate the impact of macroclimate warming on understorey communities.
We therefore assessed the functional response of understorey plant communities to warming and light addition in a full factorial experiment installed in temperate deciduous forests across Europe along natural microclimate, light and macroclimate gradients. Furthermore, we related these functional responses to the species’ life‐history syndromes and thermal niches.
We found no significant community responses to the warming treatment. The light treatment, however, had a stronger impact on communities, mainly due to responses by fast‐colonizing generalists and not by slow‐colonizing forest specialists. The forest structure strongly mediated the response to light addition and also had a clear impact on functional traits and total plant cover.
The effects of short‐term experimental warming were small and suggest a time‐lag in the response of understorey species to climate change. Canopy disturbance, for instance due to drought, pests or logging, has a strong and immediate impact and particularly favours generalists in the understorey in structurally complex forests.
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Abstract
Aim
Ellenberg indicator values (
EIV
) are frequently used in regions outside their Central European origin as proxies for environmental conditions, a practice further boosted by the ...increasing scientific focus on global change. The performance of
EIV
outside their geographic origin and over long gradients has, however, rarely been tested. The aim of this study was to evaluate if the indicative power of
EIV
changes over a large geographic gradient and to analyse the potential causes of such changes.
Location
Sweden.
Taxon
Vascular plants.
Methods
We used data on forest understorey vegetation and soils from >15,000 plots from the Swedish National Forest Inventory to model how the relationship between community mean
EIV
and measured environmental variables changes along an extensive latitudinal gradient (>15°). We used Generalized Additive Mixed Models to account for the inventory design, and for potential nonlinearities in the relationship between the mean
EIV
and the environmental variables. Additionally, Huisman–Olff–Fresco (
HOF
) models were developed for the relationship between the incidence probability and the environmental variables to analyse if the widths of species niches change along the geographic gradient.
Results
Our study shows that
EIV
for N (nutrients), R (
pH
) and T (temperature) are useful as far north as the Arctic Circle, while those for K (continentality) showed a much weaker relationship with measured continentality. However, the indicative power of the
EIV
for N and R gradually became weaker towards the north along with shifts towards larger environmental niche widths of the indicator species.
Main conclusions
EIV
are useful indicators of soil conditions in boreal forests located far north of Central Europe. However, the drop in indicative power in the northernmost regions due to increasing environmental niche widths needs to be taken into account when applying
EIV
along long geographic gradients to avoid spatial bias.
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Linear landscape elements such as hedgerows and road verges have the potential to mitigate the adverse effects of habitat fragmentation and climate change on species, for instance, by serving as a ...refuge habitat or by improving functional connectivity across the landscape. However, so far this hypothesis has not been evaluated at large spatial scales, preventing us from making generalized conclusions about their efficacy and implementation in conservation policies.
Here, we assessed plant diversity patterns in 336 vegetation plots distributed along hedgerows and road verges, spanning a macro‐environmental gradient across temperate Europe. We compared herb‐layer species richness and composition in these linear elements with the respective seed‐source (core) habitats, that is, semi‐natural forests and grasslands. Next, we assessed how these differences related to several environmental drivers acting either locally, at the landscape level or along the studied macro‐ecological gradient.
Across all regions, about 55% of the plant species were shared between forests and hedgerows, and 52% between grasslands and road verges. Habitat‐specialist richness was 11% lower in the linear habitats than in the core habitats, while generalist richness was 14% higher. The difference in floristic composition between both habitat types was mainly due to species turnover, and not nestedness. Most notably, forest‐specialist richness in hedgerows responded positively to tree cover, tree height and the proportion of forests in the surrounding landscape, while generalist richness was negatively affected by tree height and buffering effect of trees on subcanopy temperatures. Grassland and road verge diversity was mainly influenced by soil properties, with positive effects of basic cation levels on the number of specialists and those of bioavailable soil phosphorus on generalist diversity.
Synthesis and applications. We demonstrate that linear landscape elements provide a potential habitat for plant species across Europe, including slow‐colonizing specialists. Additionally, our results stress the possibility for land managers to modify local habitat features (e.g. canopy structure, subcanopy microclimate, soil properties, mowing regime) through management practices to enhance the colonization success of specialists in these linear habitats. These findings underpin the management needed to better conserving the biodiversity of agricultural landscapes across broad geographical scales.
We demonstrate that linear landscape elements provide a potential habitat for plant species across Europe, including slow‐colonizing specialists. Additionally, our results stress the possibility for land managers to modify local habitat features (e.g. canopy structure, subcanopy microclimate, soil properties, mowing regime) through management practices to enhance the colonization success of specialists in these linear habitats. These findings underpin the management needed to better conserving the biodiversity of agricultural landscapes across broad geographical scales.
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Forest biodiversity world‐wide is affected by climate change, habitat loss and fragmentation, and today 20% of the forest area is located within 100 m of a forest edge. Still, forest edges harbour a ...substantial amount of terrestrial biodiversity, especially in the understorey. The functional and phylogenetic diversity of forest edges have never been studied simultaneously at a continental scale, in spite of their importance for the forests' functioning and for communities' resilience to future change.
We assessed nine metrics of taxonomic, phylogenetic and functional diversity of understorey plant communities in 225 plots spread along edge‐to‐interior gradients in deciduous forests across Europe. We then derived the relative effects and importance of edaphic, stand and landscape conditions on the diversity metrics.
Here, we show that taxonomic, phylogenetic and functional diversity metrics respond differently to environmental conditions. We report an increase in functional diversity in plots with stronger microclimatic buffering, in spite of their lower taxonomic species richness. Additionally, we found increased taxonomic species richness at the forest edge, but in forests with intermediate and high openness, these communities had decreased phylogenetic diversity.
Functional and phylogenetic diversity revealed complementary and important insights in community assembly mechanisms. Several environmental filters were identified as potential drivers of the patterns, such as a colder macroclimate and less buffered microclimate for functional diversity. For phylogenetic diversity, edaphic conditions were more important. Interestingly, plots with lower soil pH had decreased taxonomic species richness, but led to increased phylogenetic diversity, challenging the phylogenetic niche conservatism concept.
Synthesis. Taxonomic, phylogenetic and functional diversity of understorey communities in forest edges respond differently to environmental conditions, providing insight into different community assembly mechanisms and their interactions. Therefore, it is important to look beyond species richness with phylogenetic and functional diversity approaches when focusing on forest understorey biodiversity.
Overzicht
Wereldwijd ondervindt de biodiversiteit in bossen een invloed van klimaatsverandering, habitatverlies en fragmentatie en vandaag bevindt reeds 20% van de oppervlakte bos zich dichter dan 100 m bij een bosrand. Toch bevatten bosranden een substantieel aandeel van de terrestrische biodiversiteit, voornamelijk in de kruidlaag. De functionele en fylogenetische diversiteit van bosranden werd nog niet eerder tegelijkertijd met taxonomische soortendiversiteit onderzocht op een continentale schaal, ondanks het belang van functionele en fylogenetische aspecten voor het functioneren van bossen en de veerkracht van gemeenschappen.
Wij onderzochten negen maten voor taxonomische, fylogenetische en functionele diversiteit van plantengemeenschappen in de kruidlaag in 225 plots langsheen bosrand‐tot‐boskern gradiënten in loofbossen verspreid doorheen Europa. Voor deze maten werd het relatieve effect en belang onderzocht van bodem‐, bosbestand‐ en landschaps‐karakteristieken.
Hier tonen wij aan dat taxonomische, fylogenetische en functionele diversiteitmaten verschillend beïnvloed worden door milieufactoren. We rapporteren een stijging van de functionele diversiteit in een sterker gebufferd microklimaat, ondanks de lagere taxonomische soortenrijkdom. Bovendien was de taxonomische soortenrijkdom hoger aan de bosrand, maar hadden deze plantgemeenschappen een lagere fylogenetische diversiteit in bosranden met intermediaire tot hoge openheid van het bladerdek.
De functionele en fylogenetische diversiteitmaten brachten complementaire en belangrijke inzichten naar voren omtrent de samenstellingsmechanismen van deze gemeenschappen. Verschillende milieu filters werden geïdentificeerd als potentiële mechanismes, zoals een kouder macroklimaat en minder gebufferd microklimaat voor functionele diversiteit. Voor fylogenetische diversiteit waren eigenschappen van de bodem dan weer meer belangrijk. Plantengemeenschappen in plots met een lagere bodem pH hadden een lagere taxonomische soortenrijkdom, maar een hogere fylogenetische diversiteit.
Synthese. Bosrand‐tot‐boskern gradiënten en milieufactoren beïnvloeden de taxonomische, fylogenetische en functionele diversiteit van gemeenschappen in de kruidlaag op verschillende wijze. Daarom is het belangrijk om voorbij taxonomische soortenrijkdom te kijken bij het bestuderen van de biodiversiteit van plantengemeenschappen in de kruidlaag.
Taxonomic, phylogenetic and functional diversity of understorey communities in forest edges respond differently to edge‐to‐interior gradients and environmental conditions, providing insight into different community assembly mechanisms and their interactions. Therefore, it is important to look beyond species richness with phylogenetic and functional diversity approaches when focusing on forest understorey biodiversity.
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In many agricultural landscapes, it is important to restore networks of forests to provide habitat and stepping stones for forest specialist taxa. More knowledge is, however, needed on how to ...facilitate the immigration of such taxa in restored forest patches. Here, we present the first chronosequence study to quantify the dynamics of immigration credits of forest specialist plants in post‐arable forest patches.
We studied the distribution of herbaceous forest specialist plant species in 54 post‐arable broadleaved forest patches along gradients of age (20–140 years since forest establishment), distance from ancient forest (0–2,600 m) and patch area (0.5–9.6 ha). With linear mixed models, we estimated the effects of these factors on species richness, patch means of four dispersal‐related plant traits and with generalized linear models on the occurrence of 20 individual species.
Post‐arable forest patch age and spatial isolation from ancient forest, but not patch size, were important predictors for species richness of forest specialists, suggesting that also small patches are valuable for habitat connectivity. Compared to species richness in ancient forest stands, the immigration credit was reduced by more than 90% after 80 years in post‐arable forest patches contiguous to ancient forest compared to 40% after 80 years and 60% after 140 years in isolated patches (at least 100 m to next forest). Tall‐growing species with adaptations to long‐distance dispersal were faster colonizers, whereas species with heavy diaspores and clonal growth were slower to colonize.
Synthesis and applications. We show that post‐arable oak plantations have a high potential for restoration of forest herb vegetation. Dispersal‐related plant traits play a key role in explaining interspecific differences among forest specialists. To facilitate forest herb immigration across all functional groups in agricultural landscapes, we suggest to create clusters of relatively small new forest patches nearby older forest with source populations.
We show that post‐arable oak plantations have a high potential for restoration of forest herb vegetation. Dispersal‐related plant traits play a key role in explaining interspecific differences among forest specialists. To facilitate forest herb immigration across all functional groups in agricultural landscapes, we suggest to create clusters of relatively small new forest patches nearby older forest with source populations.
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Boreal forests form the largest and least disturbed forest biome in the northern hemisphere. However, anthropogenic pressure from intensified forest management, eutrophication, and climate change may ...alter the ecosystem functions of understory vegetation and services boreal forests provide. Swedish forests span long gradients of climate, nitrogen deposition, and management intensity. This makes them ideal to study how the species composition and functions of other, more pristine, boreal forests might change under increased anthropogenic pressure. Moreover, the National Forest Inventory (NFI) has collected systematic data on Swedish forest vegetation since the mid-20th century. We use this data to quantify changes in vegetation types between two periods, 1953–1962 and 2003–2012. The results show changes in forest understory vegetation since the 1950s at scales not previously documented in the boreal biome. The spatial extent of most vegetation types changed significantly. Shade-adapted and nutrient-demanding species (those with high specific leaf area) have become more common at the expense of light-demanding and nutrient-conservative (low specific leaf area) species. The cover of ericaceous dwarf shrubs decreased dramatically. These effects were strongest where anthropogenic impacts were greatest, suggesting links to drivers such as nitrogen deposition and land-use change. These changes may impact ecosystem functions and services via effects on higher trophic levels and faster plant litter decomposition in the expanding vegetation types. This, in turn, may influence nutrient dynamics, and consequently ecosystem productivity and carbon sequestration.
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•Green Tree retention (GTR) is a conservation action widely used in production forests.•Previous studies on GTR are from clear-cuts, in this study we evaluated mid-aged stands.•Stands with GTR had a ...higher bird abundance and species richness than control stands.•GTR also benefited important guilds as broadleaf-specialists and cavity nesters.•However, several factors limited the capacity to detect threshold requirements for GTR.
Retention forestry involves saving important forest structures for flora and fauna during the final felling of a stand, including dead wood and variable amounts of living trees, i.e. green tree retention (GTR). Here we evaluate the long-term effects on avian diversity from GTR by surveying forest birds in 32 mid-rotation stands in southern Sweden, in which broadleaf GTR was present or absent. Complementing the many studies that have assessed GTR in clear-cuts, our results indicated that bird assemblages can also benefit from broadleaf GTR several decades after final felling in conifer dominated production stands. The GTR stands harboured a higher bird abundance and species richness than the control stands without GTR, and also appears to have benefited several important guilds, such as broadleaf-associated birds and cavity nesters. However, variation in the number trees retained, the species composition of retained trees, and their environmental context within the stand (e.g. density and proximity of surrounding production trees), limited our capacity to detect threshold requirements for GTR. In summary, our study provides a “glimpse into the future” as mid-rotation production stands with such old and large retained trees are unusual in today's landscape, but are expected to become more common in the decades to come, in Sweden and many other nations. Our study thereby provides provisional support for the continued and future use of this practice, and indicates that the biodiversity contribution of retention trees continues to occur several decades into the stand’s rotation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Questions
Does the influence of forest edges on plant species richness and composition depend on forest management? Do forest specialists and generalists show contrasting patterns?
Location
Mesic, ...deciduous forests across Europe.
Methods
Vegetation surveys were performed in forests with three management types (unthinned, thinned 5–10 years ago and recently thinned) along a macroclimatic gradient from Italy to Norway. In each of 45 forests, we established five vegetation plots along a south‐facing edge‐to‐interior gradient (n = 225). Forest specialist, generalist and total species richness, as well as evenness and proportion of specialists, were tested as a function of the management type and distance to the edge while accounting for several environmental variables (e.g. landscape composition and soil characteristics). Magnitude and distance of edge influence were estimated for species richness per management type.
Results
Greatest total species richness was found in thinned forests. Edge influence on generalist plant species richness was contingent on the management type, with the smallest decrease in species richness from the edge‐to‐interior in unthinned forests. In addition, generalist richness increased with the proportion of forests in the surrounding landscape and decreased in forests dominated by tree species that cast more shade. Forest specialist species richness, however, was not affected by management type or distance to the edge, and only increased with pH and increasing proportion of forests in the landscape.
Conclusions
Forest thinning affects the plant community composition along edge‐to‐interior transects of European forests, with richness of forest specialists and generalists responding differently. Therefore, future studies should take the forest management into account when interpreting edge‐to‐interior because both modify the microclimate, soil processes and deposition of polluting aerosols. This interaction is key to predict the effects of global change on forest plants in landscapes characterized by the mosaic of forest patches and agricultural land that is typical for Europe.
In Europe, forests are highly fragmented and are often managed. We studied in 9 regions, from Norway to Italy, if edge influence on the understorey depends on forest management. Thinning as forest management did not affect forest specialist species richness negatively in ancient forests, while generalists showed a contrasting pattern.
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Climate change is pushing species towards and potentially beyond their critical thermal limits. The extent to which species can cope with temperatures exceeding their critical thermal limits is still ...uncertain. To better assess species' responses to warming, we compute the warming tolerance (ΔTniche) as a thermal vulnerability index, using species' upper thermal limits (the temperature at the warm limit of their distribution range) minus the local habitat temperature actually experienced at a given location. This metric is useful to predict how much more warming species can tolerate before negative impacts are expected to occur. Here we set up a cross‐continental transplant experiment involving five regions distributed along a latitudinal gradient across Europe (43° N–61° N). Transplant sites were located in dense and open forests stands, and at forest edges and in interiors. We estimated the warming tolerance for 12 understory plant species common in European temperate forests. During 3 years, we examined the effects of the warming tolerance of each species across all transplanted locations on local plant performance, in terms of survival, height, ground cover, flowering probabilities and flower number. We found that the warming tolerance (ΔTniche) of the 12 studied understory species was significantly different across Europe and varied by up to 8°C. In general, ΔTniche were smaller (less positive) towards the forest edge and in open stands. Plant performance (growth and reproduction) increased with increasing ΔTniche across all 12 species. Our study demonstrated that ΔTniche of understory plant species varied with macroclimatic differences among regions across Europe, as well as in response to forest microclimates, albeit to a lesser extent. Our findings support the hypothesis that plant performance across species decreases in terms of growth and reproduction as local temperature conditions reach or exceed the warm limit of the focal species.
The warming tolerances of understory plant species varied with macroclimatic differences among regions across Europe, as well as in response to forest microclimates, albeit to a lesser extent. Plant performance across species decreases in terms of growth and reproduction as local temperature conditions reach or exceed the warm limit of the focal species.
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