Estimates from hemispherical photographs of the radiation climates of some bryophyte habitats. in the British Isles

Abstract

Data from hemispherical (‘fisheye’) photographs are presented from twenty bryophyte sites, including open grassland and rock outcrops of various slopes and aspects, habitats of mountain species on shaded cliffs and in corries, and wooded habitats of lowland atlantic species. These demonstrate effects of slope and aspect on both instantaneous and total energy income in direct sunshine, especially marked during the winter half of the year. Corrie habitats of northern atlantic species such as Herberta adunca and Mastigophora woodsii were exposed to direct sun only for a limited period in summer, with peak direct irradiance in June (about half that for an unobstructed level site in the examples considered). Wooded habitats of lowland atlantic species received their peak irradiance (both direct and diffuse) immediately before leaf expansion in spring; direct irradiance at this period relative to an unobstructed level site ranged from 0.8 (instantaneous)/0.35 (daily total) (Plagiochila spinulosa, Scapania gracilis: Devon) down to negligible values (Drepanolejeunea hamatifolia, Aphanolejeunea microscopica; ravine sites in N. Wales and Yorkshire).