Microclimatic refugia in riparian woodland: A climate change adaptation strategy

There is increasing interest in the role that microclimatic refugia might play in moderating the response of biodiversity to climate change. A key question is how habitat management can proactively generate microclimatic refugia to maintain locally favourable conditions despite macroclimatic change. This study uses woodland epiphytes as a case-study, to answer this question. Field sampled data documented a cross-scale response of the conservation-priority lichen - Lobaria pulmonaria - to macroclimate, and, representing microclimates, the distance to watercourse and bryophyte association. The field sampled response was tested against experimental growth rates in a factorial design with respect to two climatically-contrasting sites (Benmore and Dawyck Botanic Gardens, in northern Britain), four watercourse distances, for lichens with and without bryophyte association. When measured for a summer dry period, the sites, watercourse distances and bryophyte associations had significantly different vapour pressure deficit (VPD) experienced by the lichen thalli, and therefore affecting physiological response. Furthermore, the field sampled response and growth rates were consistent, supporting the use of riparian woodland with a buffer of c. 500 m as an adaptation option that would allow lichen populations to adjust position (further or nearer from a watercourse) as they migrate locally into microclimatic space when responding to macroclimatic change. Microhabitat complexity (areas with and without bryophytes) would facilitate this process. These results are relevant to rare and threatened conservation priority epiphytes - including temperate rainforest species - lending additional support to the bundle of ecosystem services provided by riparian woodland.