Trends of vegetation change in colline and submontane climax forests in Switzerland

2001

S. 3-12

3 Abb., 2 Tab., 32 Lit. Ang.

Unselbständiges Werk

200088847

1. The present study analyses overall trends of vegetation change during the second half of the 20th century in forests of the Swiss Midlands. 2. On an east-west transect across the Swiss Midlands, forest sites where the vegetation had been surveyed during the period 1940-1965 with the Braun-Blanquet method were resurveyed in 1998, excluding sites with obvious traces of forest management or other disturbance (in total 37 sites). Changes in species composition were evaluated in terms of presence or absence of species, species richness, growth forms and average ecological indicator values. 3. Species composition changed considerably between 1940-1965 and 1998, with 184 of the totally 241 species becoming less frequent and 44 species becoming more frequent. The average number of species per relevé decreased from 41 to 26 between the two periods. 4. According to average ecological indicator values, habitat conditions became moister, richer in nutrients, and generally darker. The observed trends generally point to more mesic conditions, which coincides with the natural life cycle of forests in increasingly mature stage. 5. A decreasing number of montane species, an increasing number of thermophilous species and the apparition of several evergreen broad-leaved exotic species together strongly suggest a change towards warmer conditions. This result in consistent with trends observed in other recently published studies on vegetation change within Swiss lowland forests and may reflect climate change.