Response of epiphytic lichens to 21st Century climate change and tree disease scenarios

Abstract

Characterising the future risk to biodiversity across multiple environmental drivers is fraught with uncertainty and is a major conservation challenge. Scenario planning - to identify robust decisions across a range of plausible futures - can aid biodiversity conservation when tactical decisions need to be made in the present-day, yet consequences are realised over many decades. Management responses to the impact of tree disease are an excellent candidate for scenario planning, because actions to reduce an imminent biodiversity threat need to be effective in the long-term by accounting for concomitant factors such as a changing climate. Lichen epiphytes were used to exemplify a guild sensitive to woodland change, such as a tree disease impact. Bioclimatic models for 382 British epiphytes were combined with species-specific tree association values, to explore scenarios of tree disease (ash dieback), climate change, and range-filling under a lower SO2 pollution regime, for northern Britain focussed on Scotland. Results indicated: 1. Exposure of lichen diversity to projected climate change is spatially structured and expected to be greater in continental northeast Scotland, compared to oceanic western Scotland. 2. Impact of tree disease showed analogous geographic trends, evidencing a critical interaction between the climatic and local ecological setting. On average, the loss of ash could have an effect on epiphyte assemblages comparable in magnitude to that of climate change under a 2080s high emissions scenario. 3. In general, tree disease impacts can be mitigated by increasing the diversity of substitute tree species within a stand, to generate complementarity among epiphyte communities. However, the effectiveness of alternate management scenarios varied locally between sites and temporally with the progression of climate change. Given this variability, scenario analysis is recommended to effectively manage for resilience, by scoping how local factors (e.g. managed woodland composition) can reduce epiphyte assemblage turnover beyond that uniquely associated with larger-scale environmental impacts. (C) 2014 Elsevier Ltd. All rights reserved.