Variation in Betula pubescens Ehrh. (Betulaceae) in Scotland: its nature and association with environmental factors

Abstract

A classification, based on climatological, topographical and geological attributes and developed by Bunce, Barr & Whittaker (1981: Annual Report of the Institute of Terrestrial Ecology, U.K. 1980) for stratifying the U.K. into 32 land classes, was used to ensure objectivity when sampling the range of variation within Betula spp. in northern Britain. Seeds of Betula spp. were collected, wherever possible, from each of ten woodland trees in three geographically distinct locations of each of 12 land classes known to ‘carry’Betula species. Trees in a thirteenth land class, restricted to the west of Scotland, were inaccessible. Seedlings from 170 of 196 trees were attributed to B. pubescens which occurred in all 12 land classes: the remaining 26 trees were identified as B. pendula which is restricted to five land classes in southern and eastern Scotland. Detailed analyses of plant morphological and phenological features using principal component analyses, cluster analyses and canonical variance analyses showed that leaf size, shape and hairiness were good discriminators of variation, as was the occurrence of fruitbodies of Laccaria proxima, a sheathing (ecto-)mycorrhizal fungus. These discriminators enabled the seedlings to be arranged in a nuniber of distinctive groups: sredlings with drooping branclirs and small laves, chararteristics of B. pubescens subspecies tortuosa, originating from westerly and wet locations to seedlings with upright branches and large leaves originating from easterly and dry locations. Leaf lengths and the increasing frequency of petiolar hairs were related to maximum July temperatures and measures of oceanicity (at the sites of origin).