PATTERNS OF DIVERSITY IN THE STRATA OF BOREAL MONTANE FOREST IN BRITISH-COLUMBIA

Patterns of diversity were analyzed in a boreal coniferous forest and its strata (tree, shrub, herb and bryophyte layers): number of species per community - alpha-diversity, total species richness - gamma-diver sity, mean similarity - beta-diversity, and mosaic diversity, a measur e of complexity. These four measures of diversity consistently decreas ed from lower to upper vegetation layers. To study the effect of juven iles of larger life forms on diversity of lower layers, they were remo ved from the data and the measures of diversity reanalyzed. Number of species per community and mosaic diversity decreased substantially, bu t beta-diversity did not change. So, the effect of juveniles on gamma- diversity is due to the greater number of species per community. Multi ple regres sion models revealed that the relationships between alpha-d iversity and the environmental variables were the same for the whole f orest and for the herb layer. Elevation and soil pH were the major var iables explaining alpha-diversity in the whole community. Climate was the only environmental gradient related to species richness in all ind ividual strata. Tree and herb richness values were negatively related to soil drainage and acidity, respectively. Species richness of the pl ant community was affected by environmental variability mostly through the herb layer. Various explanations of the observed diversity patter ns included: environmental constraints, resource competition, generati on time, and colonization processes.