Data from: To the top or into the dark? Relationships between elevational and canopy cover distribution shifts in mountain forests

Numerous studies have reported that observed species shifts in mountain
areas lag behind expectations under current warming trends, however, the
mechanisms remain poorly understood. One important mechanism might be
microclimatic heterogeneity causing migration of species to cooler
conditions under closed forest canopies; however, evidence is scarce. We
here compared the distributions of 710 species (11 taxonomic groups
including fungi, plants, and animals) along an elevation gradient
(287-1,419 m a.s.l.) in a temperate low mountain range between 2006-2008
and 2016-2017 to address this open question. We characterized each
species’ distribution (peak and breadth) based on their abundance along
two environmental gradients: elevation and canopy cover. We then analysed
changes in species’ distribution peaks, asking whether shifts in canopy
distribution and initial distribution characteristics explain variation in
elevational distribution shifts. Across all taxa, the mean shift in
elevational distribution peak was +35.3 metres (i.e., upslope).
Species' baseline distribution peaks were strong predictors of
elevational distribution shifts with stronger upslope shifts in
low-elevation and open-forest species. Even though we observed
considerable variation in the responses among species, canopy distribution
shifts had a significant negative effect on elevational distribution
shifts overall and in six taxonomic groups. We suggest that this is
related to cooler microclimatic conditions under closed compared to open
forest canopies. Shifts to closed-canopy forests may thus partly
compensate for elevational distribution shifts, highlighting the
conservation value of heterogeneous landscapes featuring microclimatic
refugia. Yet, it is likely that other mechanisms, such as habitat
limitation, are also at play. Future studies need to quantify the
potential of microclimatic refugia under accelerating forest dynamics
considering the interplay of canopy cover and other factors
driving microclimate and to illuminate the complex climate change response
mechanisms among species and taxonomic groups.