Sharp and Gradual Mountain Timberlines as a Result of Species Interaction

Abstract

Russian scientists have been interested in transition zones between adjacent natural complexes for more than a century. Distinguished geographers, geobotanists, and soil scientists investigated, in particular, the problem of sharp and gradual transitions. The factors controlling ecotone sharpness remain debatable today. The classical work on the chernozem soils (black earths) in the European part of Russia (Dokuchaev 1983) emphasizes that boundaries between soil types are gradual transitions. In botanical literature, it has been established that natural timberlines can be either clearly pronounced or gradual (Vysotsky 1909). The degree of sharpness of geographical boundaries was used as an important characteristic for their classification (Semenov-Tian-Shansky 1928). D.L. Armand (1955) suggested a quantitative index to denote the degree of gradual transition from one landscape type to another. Most of the geobotanists accepted the concept of vegetation cover as a continuum divided into communities not so much by the boundaries as by the gradients of gradual quantitative changes (Vasilevich 1967, Aleksandrova 1969, Mirkin and Rozenberg 1978). Some of the botanists and geographers—landscape-specialists hold an opposite point of view, however. They believe that abrupt transitions are typical of natural systems (Solntsev 1949, Razumovsky 1981).