10.2.2004: Forschung CH

Wertvolle Randstrukturen




Georg von Arx, Andreas Bosshard, Hansjörg Dietz

Eine Rastererhebung der Artenzusammensetzung auf einem landwirtschaftlichen Betrieb im Kanton Aargau zeigte die grosse Bedeutung von Randstrukturen für die Artenvielfalt. Randstrukturen hatten die grösste mittlere Diversität pro Untersuchungsfläche und enthielten 93% der gefundenen 180 Pflanzenarten. 45% der Pflanzenarten kamen nur in Randstrukturen vor.


1) Agroecosystems have long been viewed as sites of low biodiversity, but their importance for landscape-level diversity is now increasingly recognised. However, our knowledge of the determinants of biodiversity in these widespread and thus important ecosystems is still fragmentary. Land-use intensity and landscape structure seem to be the most important factors.
2) The objective of this study was to examine how the diversity of the vegetation varies within a typical farmland of Central Switzerland (30 ha, with crop fields, pastures and meadows) and to analyse how land-use type and distance from border structures influence these patterns.
3) The vegetation of the study area was surveyed in 481 quadrats (1 m2) according to a systematic grid design (25 m mesh width). The land-use of these quadrats was categorized into five classes of increasing land-use intensity. Four measures of vegetation diversity were calculated: Shannon’s diversity index (alpha diversity), species richness, evenness, and floristic dissimilarity among nearby samples (beta diversity). GIS was used to relate the spatial patterns of vegetation to land-use intensity and distance from border structures (such as field and pasture margins or forest edges).
4) A total of 180 non-woody and non-crop vascular plant species were recorded in the study area. The border structures had a comparatively high species richness: they supported 93% of the 180 species although their area accounted only for 3% of the farmland. In contrast, the managed area (97% of the area) included only 55% of the species. Vegetation diversity (both alpha and beta diversity) was negatively related to land-use intensity and tended to decrease from the margins of the study area towards its centre.
5) The key determinant for vegetation diversity in agroecosystems seems to be land-use intensity. Less intensively used spots such as border structures play a crucial role as species reservoirs despite their small area. They may even have some positive ‘radiative’ effects on vegetation diversity in farmland with a high proportion of border structures.

Keywords:
agro-ecosystems, border structures, GIS, spatial distribution

Art der Publikation:
Diplomarbeit

Literatur:
Von Arx G., Bosshard A., Dietz H. (2002): Land-use intensity and border structures as determinants of vegetation diversity in an agricultural area. Bulletin of the Geobotanical Institute ETH 68, S. 3-16.

Kontaktadresse:
Dr. Hansjörg Dietz, Geobotanisches Institut, ETH Zürich, Zürichbergstrasse 38, CH-8044 Zürich
dietz@geobot.umnw.ethz.ch
Tel: +41 (0)1 632 59 75
Fax: +41 (0)1 632 12 15

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