Observed Changes in Vegetation in Relation to Climate Warming

Abstract

The authors analyse the changes in forest vegetation in the north and south of the Alps by comparing 300 vegetation relevés of the forties and sixties with relevés of the nineties. The resulting changes in species composition and vegetation structure can be explained by various factors, one of which is the milder winter climate of the last three decades.

At these examples, the connection between similar bicolimates and the concept of the “chorological tension”, the authors make some prognoses of laurophyllisation in western Eurasia.

Introduction

In 1987, forest stands with an amazing richness in laurophyllous species were found in the Canton of Ticino. This vegetation represents the most thermophilous forest type on common soils in the southern part of the Alps (Carraro & Gianoni 1987; Gianoni et al. 1988).

The investigation of a probable reference value of thermophilous forest structures, especially focusing on potential climatic changes, is subject of this project. The research project is mainly based on three different topics:

• • the comparison of old relevés from 1940/60 with the present situation on the northern and the southern side of the Alps

• • the investigation of the phenomena on a regional and local scale (Locarnese)

• • the comparison with similar ecosystems and the analysis and evaluation of literature.

The research project focuses mainly on the vegetation of the colline and submontane belt in the southern part of the Swiss Alps. In this area the elevated thermic gradient provoked a new type of vegetation with particular aspects of the laurophyllous type. In this sense the northern part of the Alps can be considered as a comparable example for a colder climate.

The following questions were addressed:

• • Do any natural forest formations exist, in which effects related to the warming of the atmosphere can be detected?

• • To what degree can these effects be distinguished from other common phenomena of the development of vegetation under human influence?

• • Which criteria should be used to set up a list of species or vegetation structures as bioindicators?

• • What are the conclusions for land management, forest management and the reciprocal concessions considering socio-cultural aspects?