• Energy Research

Forest microclimates contrast strongly with the climate outside forests. To fully understand and better predict how forests' biodiversity and functions relate to climate and climate change, microclimates need to be integrated into ecological research. Despite the potentially broad impact of microclimates on the response of forest ecosystems to global change, our understanding of how microclimates within and below tree canopies modulate biotic responses to global change at the species, community and ecosystem level is still limited. Here, we review how spatial and temporal variation in forest microclimates result from an interplay of forest features, local water balance, topography and landscape composition. We first stress and exemplify the importance of considering forest microclimates to understand variation in biodiversity and ecosystem functions across forest landscapes. Next, we explain how macroclimate warming (of the free atmosphere) can affect microclimates, and vice versa, via interactions with land-use changes across different biomes. Finally, we perform a priority ranking of future research avenues at the interface of microclimate ecology and global change biology, with a specific focus on three key themes: (1) disentangling the abiotic and biotic drivers and feedbacks of forest microclimates; (2) global and regional mapping and predictions of forest microclimates; and (3) the impacts of microclimate on forest biodiversity and ecosystem functioning in the face of climate change. The availability of microclimatic data will significantly increase in the coming decades, characterizing climate variability at unprecedented spatial and temporal scales relevant to biological processes in forests. This will revolutionize our understanding of the dynamics, drivers and implications of forest microclimates on biodiversity and ecological functions, and the impacts of global changes. In order to support the sustainable use of forests and to secure their biodiversity and ecosystem services for future generations, microclimates cannot be ignored. Peer reviewed

Local factors restrain forest warming Microclimates are key to understanding how organisms and ecosystems respond to macroclimate change, yet they are frequently neglected when studying biotic responses to global change. Zellweger et al. provide a long-term, continental-scale assessment of the effects of micro- and macroclimate on the community composition of European forests (see the Perspective by Lembrechts and Nijs). They show that changes in forest canopy cover are fundamentally important for driving community responses to climate change. Closed canopies buffer against the effects of macroclimatic change through their cooling effect, slowing shifts in community composition, whereas open canopies tend to accelerate community change through local heating effects. Science , this issue p. 772 ; see also p. 711

Abstract Efforts to abate climate change heavily rely on carbon sequestration by trees. However, analyses of tree carbon dynamics often neglect trees outside of forests (TOFs) and spatially detailed information about tree carbon sequestration rates are largely missing. Here we describe a new method which combines remote sensing with forest inventory data from 127 358 sites to first estimate tree age and site productivity, which we then used to estimate carbon storage and sequestration rates for all trees inside and outside forests across Great Britain. Our models estimate carbon storage and sequestration rates with R 2 values of 0.86 and 0.56 (root-mean-square errors of 70 tCO2e ha−1 and 3.4 tCO2e ha−1 yr−1). They also reveal the important finding that 17% (165.6 MtCO2e) of the total carbon storage and 21% (3.4 MtCO2e yr−1) of the total carbon sequestration rate of all trees in Great Britain come from TOF, with particularly high contributions in England (24.3% and 34.1%), followed by Wales (12.5% and 17.6%) and Scotland (2.6% and 1.8%). Future estimates of carbon status and fluxes need to account for the significant contributions of TOF because these trees, often found in field margins and hedgerows are potentially an important carbon offset. Our novel approach enables carbon baseline assessments against which changes can be assessed at management relevant scales, improving the means to measure progress towards net zero emissions targets and associated environmental policies.

Abstract Woody species' requirements and environmental sensitivity change from seedlings to adults, a process referred to as ontogenetic shift. Such shifts can be increased by climate change. To assess the changes in the difference of temperature experienced by seedlings and adults in the context of climate change, it is essential to have reliable climatic data over long periods that capture the thermal conditions experienced by the individuals throughout their life cycle. Here we used a unique cross‐European database of 2,195 pairs of resurveyed forest plots with a mean intercensus time interval of 37 years. We inferred macroclimatic temperature (free‐air conditions above tree canopies—representative of the conditions experienced by adult trees) and microclimatic temperature (representative of the juvenile stage at the forest floor, inferred from the relationship between canopy cover, distance to the coast and below‐canopy temperature) at both surveys. We then address the long‐term, large‐scale and multitaxa dynamics of the difference between the temperatures experienced by adults and juveniles of 25 temperate tree species. We found significant, but species‐specific, variations in the perceived temperature (calculated from presence/absence data) between life stages during both surveys. Additionally, the difference of the temperature experienced by the adult versus juveniles significantly increased between surveys for 8 of 25 species. We found evidence of a relationship between the difference of temperature experienced by juveniles and adults over time and one key functional trait (i.e. leaf area). Together, these results suggest that the temperatures experienced by adults versus juveniles became more decoupled over time for a subset of species, probably due to the combination of climate change and a recorded increase of canopy cover between the surveys resulting in higher rates of macroclimate than microclimate warming. Synthesis. We document warming and canopy‐cover induced changes in the difference of the temperature experienced by juveniles and adults. These findings have implications for forest management adaptation to climate change such as the promotion of tree regeneration by creating suitable species‐specific microclimatic conditions. Such adaptive management will help to mitigate the macroclimate change in the understorey layer.