Diversity Relations of Upland Forests in the Western Great Lakes Area

Abstract

1. Regional, environmental, and temporal gradients of species diversity were examined for upland forests of the western Great Lakes area. Tree, shrub, and herb data for 353 stands were analyzed with emphasis given to community processes regulating diversity levels. 2. The relationship between commonly employed diversity indices was examined. Dominance was shown to be highly related to equitability diversity. Types of diversity other than species-based measures were suggested. 3. A great significance was attached to changes in diversity across time and space. Diversity increased across time in pioneer forests on xeric sites. In successional forests diversity increased through time but decreased in the climax stage. This pattern was interpreted in terms of the capability of terminal species to monopolize environmental requisites. A time-space-diversity model was developed and its implications discussed in relation to recent ecological hypotheses on diversity changes with succession and environmental stress. 4. Pronounced correlations between tree, shrub, and herb diversity depended on inherent structural and dynamic characteristics of forests in different regions. Shrub or herb diversity was least in climax evergreen stands of Tsuga canadensis and greatest in successional deciduous forests. 5. Interregional comparisons of tree diversity indicated that (a) forests on xeric sites were equally low in southern, northern, and boreal transition forests; (b) tree diversity in climax southern and northern forests depended on levels of stand occupancy; and (c) ecological specialization is greatest in the northern forests.