Vascular plant species richness in relation to altitudinal and slope gradients in mountain landscapes of central norway

Abstract

Local plant ecological investigations in the central Norwegian mountains in 1992–1997 have shown some interesting features regarding the variability of vascular plant species richness along altitudinal gradients. The material reveals two peaks of vascular plant species richness with increasing elevation, a lowland peak at 0–400 m a.s.l. and a peak at the timberline area (upper part of the northern boreal zone), around the inflection line. Mountains with highly acidic bedrock have a vegetation discontinuity around the transition between discontinuous and continuous permafrost (1500 m in the Dovrefjell area), with a change from dwarf shrubs to more graminoid life forms. The angle of slope is decisive for soil-forming processes. The instability of steep slopes prevents the formation and accumulation of organic top-soils. The data show a high, positive correlation between the slope of habitat plots and the richness of vascular plant species, in both the forested and the alpine zones. A working hypothesis is put forward that, due to high substratum instability, steep terrain encourages high species richness due to the greater ‘openness’ of habitats and the higher pH of the top-soils. It is suggested that this effect of local topography on species richness is strongest around the inflection line.