• Energy Research

Forests play a key role in global carbon cycling and sequestration. However, the potential for carbon drawdown is affected by forest fragmentation and resulting changes in microclimate, nutrient inputs, disturbance and productivity near edges. Up to 20% of the global forested area lies within 100 m of an edge and, even in temperate forests, knowledge on how edge conditions affect carbon stocks and how far this influence penetrates into forest interiors is scarce. Here we studied carbon stocks in the aboveground biomass, forest floor and the mineral topsoil in 225 plots in deciduous forest edges across Europe and tested the impact of macroclimate, nitrogen deposition and smaller-grained drivers (e.g. microclimate) on these stocks. Total carbon and carbon in the aboveground biomass stock were on average 39% and 95% higher at the forest edge than 100 m into the interior. The increase in the aboveground biomass stock close to the edge was mainly related to enhanced nitrogen deposition. No edge influence was found for stocks in the mineral topsoil. Edge-to-interior gradients in forest floor carbon changed across latitude: carbon stocks in the forest floor were higher near the edge in southern Europe. Forest floor carbon decreased with increasing litter quality (i.e. high decomposition rate) and decreasing plant area index, whereas higher soil temperatures negatively affected the mineral topsoil carbon. Based on high-resolution forest fragmentation maps, we estimate that the additional carbon stored in deciduous forest edges across Europe amounts to not less than 183 Tg carbon, which is equivalent to the storage capacity of 1 million ha of additional forest. This study underpins the importance of including edge influences when quantifying the carbon stocks in temperate forests and stresses the importance of preserving natural forest edges and small forest patches with a high edge-to-interior surface area.

AbstractThe functional composition of plant communities is commonly thought to be determined by contemporary climate. However, if rates of climate‐driven immigration and/or exclusion of species are slow, then contemporary functional composition may be explained by paleoclimate as well as by contemporary climate. We tested this idea by coupling contemporary maps of plant functional trait composition across North and South America to paleoclimate means and temporal variation in temperature and precipitation from the Last Interglacial (120 ka) to the present. Paleoclimate predictors strongly improved prediction of contemporary functional composition compared to contemporary climate predictors, with a stronger influence of temperature in North America (especially during periods of ice melting) and of precipitation in South America (across all times). Thus, climate from tens of thousands of years ago influences contemporary functional composition via slow assemblage dynamics.

Climate warming is affecting ecosystems worldwide, and slow‐colonizing forest understorey species are particularly vulnerable if they are unable to track climate change. However, species' responses to climatic conditions in terms of growth, reproduction and colonization capacity may vary with the distance to their distribution range edge. Anemone nemorosa is known to be a slow colonizing forest herb dependent on forest cover in the southern and central part of its distribution range, whereas at its northern distribution range (and at higher elevations) it also occurs in open habitats. Here, we investigated the response of plant functional traits of Anemone nemorosa in central Norway (close to its northern distribution range edge) to a macroclimatic gradient (elevation), two microclimatic gradients (forest density and distance to forest edge) and a competition treatment (removal of neighbouring vegetation). We aimed to identify which environmental conditions (light, temperature, soil pH and/or soil organic matter) drive A. nemorosa's responses. In a total of 90 plots, we measured six functional traits of A. nemorosa (plant height, biomass, specific leaf area, seed number, seed mass,and germination percentage). We found stronger variation in environmental conditions along the macroclimatic elevational gradient, than along the microclimatic gradients of forest density and distance to forest edge, and this was also reflected in A. nemorosa's responses. Light availability, in interaction with temperature, was the key environmental variable driving plant performance, while soil conditions were less important. The competition release treatment had a negative effect on A. nemorosa in our study sites, indicating that the facilitative effect of the neighbouring vegetation may be stronger than the competitive effect. Our study suggests that A. nemorosa, close to its northern distribution range edge, has the capacity to cope with climate change through phenotypic responses, and that light and temperature are the key drivers of these responses.