Relationships between the crown condition of Sitka and Norway spruce and the environment in Great Britain: an exploratory analysis.
Two forms of multivariate analyses were used to examine the relation between condition of Sitka (Picea sitchensis) and Norway (Picea abies) spruce in Britain and their physical and chemical environment. Results of gradient analyses (detrended canonical correspondence analysis) were difficult to interpret because extreme values at a limited number of sites significantly affected results. Gradients of stand condition from good to poor were generally absent, with identified gradients mostly being from high scores of one response variable to high scores of another. Various different types of pollution were examined, but these showed no clear relation with stand condition suggesting that air pollution is not a major factor affecting crown condition of Sitka and Norway spruce in Britain. Two-way indicator species analysis (TWINSPAN) and discriminant analysis (DISCRIM) were also used. TWINSPAN was used to distinguish a number of groups of sites for each species on the basis of crown condition. Most of these groups were associated with combinations of environmental variables although, in many cases, relations were unclear. Relations with pollution variables were identified for six of the eight groups (all four groups for Sitka spruce and two of four groups of Norway spruce). Only one group (Norway spruce, intermediate crown condition) showed an exclusive relation with one or more pollution variables. The combined use of TWINSPAN and DISCRIM offers considerable potential and will be particularly useful for analysing data from monitoring exercises and information collected by large-scale surveys.