Lichen epiphyte abundance controlled by the nested effect of woodland composition along macroclimatic gradients

Understanding species climatic sensitivity is a central theme in biodiversity conservation. However, climate, and the response to climate change, is one component in a multiplicity of drivers which interact to control the occurrence of lichens. This paper investigates patterns of lichen species occurrence and abundance (for Degelia spp., Lobaria pulmonaria and Sphaerophorus globosus) in response to the simultaneous and interacting nested effect of macroclimate and local habitat quality. We show that for a very steep climatic gradient in Scotland occurrence is delimited by a climatic threshold, but also that abundance within a suitable locale is controlled by an interaction with local habitat quality. This interaction between cross-scale drivers – climate and local habitat – provides a powerful conservation tool, enabling predictive management to optimise habitat conditions, in order to offset the possible negative impacts of larger-scale environmental stress (e.g. climate change).