DOI: 10.5061/dryad.vq83bk3t5
title: Forest resilience to global warming is strongly modulated by local-scale topographic, microclimatic and biotic conditions

description: Resilience of endangered rear edge populations of cold-adapted forests in
 the Mediterranean basin is increasingly altered by extreme heatwave and
 drought pressures. It remains unknown, however, whether microclimatic
 variation in these isolated forests could ultimately result in large
 intra-population variability in the demographic responses, allowing the
 coexistence of contrasting declining and resilient trends across small
 topographic gradients. Multiple key drivers promoting spatial variability
 in the resilience of rear edge forests remain largely unassessed,
 including amplified and buffered thermal exposure induced by heat waves
 along topographic gradients, and increased herbivory pressure on tree
 saplings in defaunated areas lacking efficient apex predators. Here we
 analysed whether indicators of forest resilience to global warming are
 strongly modulated by local-scale topographic, microclimatic and biotic
 conditions. We studied a protected rear edge forest of sessile oak (Q.
 petraea), applying a suite of 20 indicators of resilience of tree
 secondary growth, including multidecadal and short-term indices. We also
 analysed sapling recruitment success, recruit/adult ratios and sapling
 thermal exposure across topographic gradients. We found large within
 population variation in secondary growth resilience, in recruitment
 success and in thermal exposure of tree saplings to heatwaves, and this
 variability was spatially structured along small-scale topographical
 gradients. Multidecadal resilience indices and curves provide useful
 descriptors of forest vulnerability to climate warming, complementing
 assessments based in the analysis of short-term resilience indicators.
 Species-specific associations of trees with microclimatic variability are
 reported. Biotic factors are key in determining long-term resilience in
 climatically-stressed rear edge forests, with strong limitation of sapling
 recruitment by increased roe deer and wild boar herbivory. Our results
 also support non-stationary effects of climate determining forest growth
 responses and resilience, showing increased negative effects of warming
 and drought over the last decades in declining stands. Our findings do not
 support scenarios predicting spatially homogeneous distributional shifts
 and limited resilience in rear-edge populations, and are more supportive
 of scenarios including spatially heterogeneous responses, characterised
 with contrasting intra-population trends of forest resilience. We conclude
 that forest resilience responses to climate warming are strongly modulated
 by local-scale microclimatic, topographic and biotic factors. Accurate
 predictions of forest responses to changes in climate would therefore
 largely benefit from the integration of local-scale abiotic and biotic
 factors.
description: We studied a protected rear edge forest of sessile oak
 (<i>Q. petraea</i>), applying a suite of 20 indicators of
 resilience of tree secondary growth, including multidecadal and short-term
 indices. We also analysed sapling recruitment success, recruit/adult
 ratios and sapling thermal exposure across topographic gradients. We found
 large within population variation in secondary growth resilience, in
 recruitment success and in thermal exposure of tree saplings to heatwaves,
 and this variability was spatially structured along small-scale
 topographical gradients. Multidecadal resilience indices and curves
 provide useful descriptors of forest vulnerability to climate warming,
 complementing assessments based in the analysis of short-term resilience
 indicators. Species-specific associations of trees with microclimatic
 variability are reported.