Habitat loss and climate change are the major driving forces of global biodiversity decline. Mountain ecosystems are vulnerable to both impacts and many montane species are known to be shifting their geographic distributions. Current studies attribute most observed upslope range shifts to global warming impacts, due to decreasing temperatures up elevational gradients. Yet, how land-use intensity varies across elevation and might also contribute to species redistribution remains understudied. Here we examined patterns of forest cover loss over the last decade as a function of elevation for global mountain ranges. Making use of Natural Earth’s physical vectors, we examined mountain ranges from five major continents. We then overlaid global forest cover (2000) and global forest cover loss (2000 - 2014) data from Global Forest Watch on to digital elevation maps (SRTM 1 Arc-Second Global) of each range, and generated forest cover/forest loss curves along the elevational gradient (at 100m elevation band intervals). Apart from the total amount of forested area (habitat quantity), we also compared forest cover percentage across elevation as an indicator of habitat quality. Based on these curves, we then created a model to predict the direction of species distribution range shifts in response to habitat loss and disturbance.
Results/Conclusions
Of 36 mountain ranges selected, peak forest loss generally overlaps with peak forest cover, indicating that areas with highest forest cover amounts also experienced the greatest disturbance. This would result in a shrinkage of available habitat for most species inhabiting those elevation bands. However, despite the overall decline in amount of forested area on either side of the peak, forest cover percentage is significantly higher at upper elevation bands relative to lower elevation bands (separated by the forest loss peak, 95%CI=7.05 ~ 22.18), suggesting that denser forests (potentially better quality habitat) are usually more likely at higher elevations. Therefore, if severe habitat loss/disturbance at the forest peak (elevation bands with highest habitat quantity) induces species range shifts, they would be more likely to shift upwards than downwards towards more intact forests (better quality habitats), which is in the same direction as predicted by the impacts of global warming. Thus, it is crucial to always consider the compounding and confounding effects of land-use changes in addition to climate change impacts when investigating the distribution range shifts across elevation and incorporate them into conservation strategies.