Microclimatic moisture and the climate change resilience of lichen epiphytes – an applied model for temperate rainforest

The biodiversity response to climate change will, for many species, be determined by continued availability of suitable microclimatic space locally, and the ability to colonise into such refugia through dispersal. This study measured and modelled microclimatic vapour pressure deficit (VPD) for three contrasting woodland study sites, to purposefully extend microclimatic modelling to lichen epiphytes. Statistical downscaling indicated that VPD is explained by macroclimatic moisture input (precipitation) and temperature (saturated vapour pressure), with important and locally modifying effects of elevation, landscape topography, and canopy structure. Allowing for over-fitting controls, niche models for lichen epiphyte abundance were improved when including microclimatic VPD in addition to precipitation. A niche model for lichen indicators – species which determine the conservation status of UK lowland temperate rainforest – was projected at a 5 m grid-scale for a climate baseline, and three climate change scenarios (2040s, RCP 4.5; 2060s, RCP 6; 2080s, RCP 8.5), over five temperate rainforest National Nature Reserves (NNRs). Resilience of each NNR was estimated as the proportion of extant microhabitats that have an equivalent or improved microclimate (relative to the climate baseline) at incrementing spatial distances from 10 to 100 m. Despite microclimatic buffering, resilience of the NNRs was found to be limited under their current configuration. Resilience was higher for more northerly (cooler) sites, and for sites with a greater woodland extent. Resilience could be further enhanced by woodland expansion for topographically variable landscapes that have been historically deforested, with tree regeneration/planting targeted to situations that offer future microclimatic refugia.