Micro-climatic determination of vegetation patterns along topographical, altitudinal, and oceanic-continental gradients in the high mountains of Norway

Abstract

Convictions on environmental determination of the Norwegian mountain vegetation are scrutinized as to new results of a long-term landscape ecological project. Some explanations are insufficient regarding different spatial scales: a) the fine-scale topography is supposed to impact the vegetation within two causal chains. 1. exposed site - thin snow cover - strong prevailing winds - enforced evapotranspiration - lack of soil moisture - drought stress - cold winters but long vegetation period, and 2. lee slope - thick snow cover - shelter against winds and low temperatures - good supply of water but short vegetation period. Quantification of soil moisture and micro-climate show that a lack in water availability is not found at any time. Instead, complex spatio-temporal temperature gradients affect the vegetation superiorly. b) Moreover, the altitudinal gradient across the alpine belts has been explained by temperature and precipitation means that are corresponding with specific changes in the vegetation. Higher elevations are principally combined with harder environmental conditions. Results of micro-climatic measurements give evidence that higher precipitation results in earlier and thicker sheltering snow cover in higher elevations. Thus, lowest temperatures are found in lower elevations as to inversions, where snow cover is thinnest and frost damage is most affecting. Vegetation determination functions by prevailing near surface temperatures. c) Finally, continental-oceanic gradients are expected to contrast in superior vegetation patterns. High precipitation in western Norway differs from lowest found in the eastern parts, indicating continental mountains being dry and warm during summer. Consequently, mountain vegetation is differentiated into oceanic and continental types. On the one hand, plant species distribution along that broad-scale gradient is statistically evident. On the other, equal topographical conditions show the same vegetation types in east and west; lichen dominated associations show similar species compositions. Similarities in environmental features are stressed as superior determinants for equality of vegetation.