• Energy Research

AbstractThe combination of drought and heat affects forest ecosystems by deteriorating the health of trees, which can lead to large‐scale die‐offs with consequences on biodiversity, the carbon cycle, and wood production. It is thus crucial to understand how drought events affect tree health and which factors determine forest susceptibility and resilience. We analyze the response of Central European forests to the 2018 summer drought with 10 × 10 m satellite observations. By associating time‐series statistics of the Normalized Difference Vegetation Index (NDVI) with visually classified observations of early wilting, we show that the drought led to early leaf‐shedding across 21,500 ± 2,800 km2, in particular in central and eastern Germany and in the Czech Republic. High temperatures and low precipitation, especially in August, mostly explained these large‐scale patterns, with small‐ to medium‐sized trees, steep slopes, and shallow soils being important regional risk factors. Early wilting revealed a lasting impact on forest productivity, with affected trees showing reduced greenness in the following spring. Our approach reliably detects early wilting at the resolution of large individual crowns and links it to key environmental drivers. It provides a sound basis to monitor and forecast early‐wilting responses that may follow the droughts of the coming decades.

AbstractAimRange shifts along elevational gradients are considered a major response of mountain species to climate change. However, empirical studies have so far mainly focused on leading edges or on species’ optima, and evidence of rear edge shifts remains scarce. Yet, the balance between leading and rear edge shifts has important consequences for conservation and co‐determines species’ extinction risk. Here, we present a comparative synthesis of range dynamics observed at both range limits.LocationGlobal.Time period1850–present.Major taxa studiedPlants, invertebrates, vertebrates.MethodsFrom the literature, we compiled elevational leading and rear edge shifts of 1,026 species observed at the same localities over the same time period. We used linear mixed‐effects models to analyse whether both range limits shifted upslope, whether leading edges shifted faster than rear edges and elevational range sizes have thus changed, whether observed shifts were linked to temperature changes, and whether shifts lagged behind temperature changes.ResultsDespite pronounced species‐specific variation, both range limits shifted upslope on average. Rates of shift did not differ between rear and leading edges, elevational range sizes thus did not change. Regional differences in temperature trends were only related to dynamics at rear edges. Yet, the stronger climate warmed regionally, the more species’ responses lagged behind expectations at both range limits.Main conclusionsOur results demonstrate that extinctions at rear edges of mountain species have at least been as common as colonizations at leading edges. The drivers of observed range limit shifts are not deducible from our data, but weak relationships with temperature trends suggest that other factors than climate warming played an additional role. These results do not relax concerns about possible detrimental effects of environmental change on mountain biodiversity and point to the importance of refocusing monitoring towards a better representation of rear edge dynamics.

AbstractThe conservation and restoration of forest ecosystems require detailed knowledge of the native plant compositions. Here, we map global forest tree composition and assess the impacts of historical forest cover loss and climate change on trees. The global occupancy of 10,590 tree species reveals complex taxonomic and phylogenetic gradients determining a local signature of tree lineage assembly. Species occupancy analyses indicate that historical forest loss has significantly restricted the potential suitable range of tree species in all forest biomes. Nevertheless, tropical moist and boreal forest biomes display the lowest level of range restriction and harbor extremely large ranged tree species, albeit with a stark contrast in richness and composition. Climate change simulations indicate that forest biomes are projected to differ in their response to climate change, with the highest predicted species loss in tropical dry and Mediterranean ecoregions. Our findings highlight the need for preserving the remaining large forest biomes while regenerating degraded forests in a way that provides resilience against climate change.

AbstractAimThe rate of climate change might exceed the migration capacity of plants, particularly where habitats became fragmented by human land use. Except for some tree species, the extent to which habitat fragmentation decreases migration rates has nevertheless been little evaluated. Here, we compare simulated migration rates of understorey herbs, which comprise the big part of temperate forest plant diversity, under varying levels of fragmentation at a continental scale.LocationEurope.MethodsWe combined simulations of demography and seed dispersal to simulate migration of 16 hypothetical forest herb species through a virtual, continuously forested landscape of 50 × 50 km and through 1179 50 × 50 km regions spanning most of the European Union's territory plus Norway and Switzerland. Each region was subdivided into a 250‐m raster of sites, which were rated as suitable to a species if covered by forest according to current land cover maps and future land cover scenarios. The 16 hypothetical species were defined by combinations of those trait values that control demographic and dispersal processes.ResultsIn continuous forests, simulated migration rates of the 16 species varied between ~95 and ~225 m/y. Current forest fragmentation was predicted to reduce migration rates to about 70% on average across the continent, but to below 25% in many parts of western and southern Europe. Under future land use, migration rates might slightly increase in economically marginal regions.Main conclusionsOur results indicate that even on a continuously forested continent most understorey herbs would be unable to track climate warming and that habitat fragmentation will reduce migration rates to values an order of magnitude lower than expected climate velocities in parts of Europe. We conclude that, instead of concentrating conservation efforts in protected areas, facilitating the movement of species through the average countryside should become a conservation priority.

Many studies report that mountain plant species are shifting upward in elevation. However, the majority of these reports focus on shifts of upper limits. Here, we expand the focus and simultaneously analyze changes of both range limits, optima, and abundances of 183 mountain plant species. We therefore resurveyed 1,576 vegetation plots first recorded before 1970 in the European Alps. We found that both range limits and optima shifted upward in elevation, but the most pronounced trend was a mean increase in species abundance. Despite huge species-specific variation, range dynamics showed a consistent trend along the elevational gradient: Both range limits and optima shifted upslope faster the lower they were situated historically, and species’ abundance increased more for species from lower elevations. Traits affecting the species’ dispersal and persistence capacity were not related to their range dynamics. Using indicator values to stratify species by their thermal and nutrient demands revealed that elevational ranges of thermophilic species tended to expand, while those of cold-adapted species tended to contract. Abundance increases were strongest for nutriphilous species. These results suggest that recent climate warming interacted with airborne nitrogen deposition in driving the observed dynamics. So far, the majority of species appear as “winners” of recent changes, yet “losers” are overrepresented among high-elevation, cold-adapted species with low nutrient demands. In the decades to come, high-alpine species may hence face the double pressure of climatic changes and novel, superior competitors that move up faster than they themselves can escape to even higher elevations.

AbstractThe long residence time of carbon in forests and soils means that both the current state and future behavior of the terrestrial biosphere are influenced by past variability in climate and anthropogenic land use. Over the last half‐millennium, European terrestrial ecosystems were affected by the cool temperatures of the Little Ice Age, rising CO2 concentrations, and human induced deforestation and land abandonment. To quantify the importance of these processes, we performed a series of simulations with the LPJ dynamic vegetation model driven by reconstructed climate, land use, and CO2 concentrations. Although land use change was the major control on the carbon inventory of Europe over the last 500 years, the current state of the terrestrial biosphere is largely controlled by land use change during the past century. Between 1500 and 2000, climate variability led to temporary sequestration events of up to 3 Pg, whereas increasing atmospheric CO2 concentrations during the 20th century led to an increase in carbon storage of up to 15 Pg. Anthropogenic land use caused between 25 Pg of carbon emissions and 5 Pg of uptake over the same time period, depending on the historical and spatial pattern of past land use and the timing of the reversal from deforestation to afforestation during the last two centuries. None of the currently existing anthropogenic land use change datasets adequately capture the timing of the forest transition in most European countries as recorded in historical observations. Despite considerable uncertainty, our scenarios indicate that with limited management, extant European forests have the potential to absorb between 5 and 12 Pg of carbon at the present day.

AbstractScientific understanding of biodiversity dynamics, resulting from past climate oscillations and projections of future changes in biodiversity, has advanced over the past decade. Little is known about how these responses, past or future, are spatially connected. Analyzing the spatial variability in biodiversity provides insight into how climate change affects the accumulation of diversity across space. Here, we evaluate the spatial variation of phylogenetic diversity of European seed plants among neighboring sites and assess the effects of past rapid climate changes during the Quaternary on these patterns. Our work shows a marked homogenization in phylogenetic diversity across Central and Northern Europe linked to high climate change velocity and large distances to refugia. Our results suggest that the future projected loss in evolutionary heritage may be even more dramatic, as homogenization in response to rapid climate change has occurred among sites across large landscapes, leaving a legacy that has lasted for millennia.