The Method of Successive Approximation in Descriptive Ecology

The vegetation of the forest-alpine transition in the Grunningsdalen area, Telemark, S. Norway

This study is divided into two parts. The general part contains a review of theories of the nature of vegetation. It is concluded that present evidence points in the direction of species individuality and vegetational continuum as responses to continuous environmental gradients, on a regional, and mostly also on a local scale. Accordingly, a gradient approach to classification of the forest and alpine vegetation of the investigated area was designed as an alternative to traditional phytosociological classification. The importance of the concept of corresponding vegetation types in different regions is stressed. It is argued that four environmental gradients explain the major variation in Southern Norwegian forest and alpine vegetation. In the special part, the vegetation of the Grunningsdalen area is treated. Two gradients, the vertical gradient and the complex-gradient topographic moisture snow cover, are considered sufficient to explain the major variation in forest and alpine vegetation in the area. The vegetation is classified into 16 site-types by division of the gradients into four zones (according to altitude) and four series (according to moisture - snow cover) by means of floristic criteria known to reflect particular ecological conditions. For each of the site-types a description of the vegetation and an extensive comparison with corresponding Fennoscandian vegetation is given. On the basis of results from the present study area regional variation in Southern Norwegian poor vegetation corresponding to the xeric, subxeric, and submesic series, and phytosociological classification in the forestalpine transition are discussed. Various numerical classification and ordination methods are used in an analysis of the floristic composition of the site-types and the autecology of the species. The main phytosociological gradient in the investigated vegetation runs from dry and high altitude to wet and low altitude, most closely approaching the moisture gradient. Diversity relations are discussed. It is strongly emphasized that a hierarchic system is unable to give a consistent classification of a vegetation that must be regarded as a multidimensional network of variation along environmental gradients. Viewed in the light of the results of this study, a gradient approach to classification seems most suitable for a variety of Fennoscandian ecosystems.