Aim To quantify the role of multiple biodiversity drivers – pollution, woodland structure and climate – controlling lichen epiphyte composition and diversity.
Location Scotland, north-west Europe.
Methods Four compatible datasets were assembled: site-scale species distribution data (response) and base-line modelled data on climate, pollution loads and extent of old-growth woodland (explanatory variables). First, partial-canonical correspondence analysis was used: (1) to compare the importance of environmental variables to pure spatial effects and (2) to partition the importance of environmental variables in explaining species composition. Secondly, patterns of species richness were investigated using multiple least-squares regression.
Results Old-growth woodland was the most important control of species richness. Pollution was the most important explanatory variable for species composition. The impact of pollution on composition (and to a lesser extent on richness) is explained: (1) By recovery of lichens with declining SO2 pollution, although with epiphyte composition shifted by the recent effects of N-pollution and (2) By the limited spatial extent of severe pollution, and generally low-to-moderate pollution loads across our study area, combined with the positive effect of old-growth woodland extent in controlling species richness. The effect of climate and old-growth woodland on species composition covaried, supporting an interaction between habitat quality and climatic setting, which may be important in understanding the epiphyte response to climate change.
Conclusions Advances in conservation planning will likely require an integrated approach to understanding simultaneous effects of multiple drivers, providing opportunities for integrated management strategies. Our study provides a preliminary example of this approach by combining three key biodiversity drivers into a single framework for lichen epiphytes. Thus, reducing pollution loads may make old-growth woodland that currently exists in a polluted landscape available for colonization, thereby extending the available habitat for epiphytes, and facilitating an effective species response to climate change.