Perspectives in Plant Ecology, Evolution and Systematics
Changes in the species composition and conservation value of limestone grasslands in Northern Switzerland after 22 years of contrasting managements
Introduction
The limestone grasslands of temperate Europe are of great interest to nature conservation because of their high species richness, including many rare and threatened species (Wolkinger and Plank, 1981). Most limestone grasslands are the product of a long history of human use, and their continued existence depends upon maintaining some suitable management such as mowing or grazing (e.g. Hegg et al., 1992; Schumacher et al., 1995; Poschlod and WalliesDeVries, 2002). In northern Switzerland, limestone grasslands were traditionally mown annually in July. However, changing economic conditions mean that this form of management is no longer economically viable, resulting in large losses of limestone grassland vegetation because of changed land use or abandonment (Klein and Keller, 1982). To reduce this trend, farmers now receive payments to maintain areas of limestone grassland, though even with these incentives new forms of management are required which minimise expense and effort.
In several European countries, field experiments have been set up to investigate the long-term influence of different types of management on limestone grasslands (Dierschke, 1985; Willems, 1985; Hansson and Fogelfors, 2000). The experiment presented in this study was set up in 1977 and 1978 (Krüsi, 1981) and has continued for over 22 years, making it one of the longest-running experiments of its kind (but see Kahmen et al., 2002, albeit with other managements). As such, this experiment is particularly valuable as a basis for developing management recommendations for the conservation of these threatened habitats. In this study, we analysed the vegetation changes under six different types of management comprising four mowing regimes, abandonment and burning. The questions addressed were: (1) How much do the different treatments change the vegetation? (2) What is the period of time needed for these changes to occur? (3) Which management regime is most similar in its effects on the vegetation to the traditional one and can therefore be used as an alternative? (4) And are the results applicable to other regions?
To answer these questions, we analysed data from vegetation relevés recorded at intervals during the course of the experiment. We used correspondence analysis (CA) to investigate trends in the plant community as a whole, and also investigated changes in the cover of individual species.
In a separate study on the same plots, B. Köhler and A. Gigon (unpubl. data) studied how changes in vegetation caused by 21 years of contrasting managements can be understood in terms of the ecological characteristics of the component plant species. The main conclusion was that in this very nutrient-poor limestone grassland, the species composition associated with a particular form of management is strongly influenced by ecological traits which help to minimise the nutrient losses. For example, infrequent mowing or burning enhances species with belowground nutrient storage; in contrast, mowing in July favours rosette forming species because losses in biomass are mainly small.
Section snippets
Study sites
The two limestone grassland sites were in northern Switzerland, 7.5 km north of Schaffhausen. One site is located on the plateau ‘Gräte’ (47°45′58″N and 8°37′03″E) at 720 m a.s.l. on a S.E.E. facing slope (20°); it is referred to here as Gräte. The second study site is at the bottom of a S.E.E. facing slope (30°) at 580 m a.s.l. in ‘Grätental’ (47°45′46″N and 8°37′10″E).
The grassland vegetation type of Gräte is a ‘Medicago falcatae-Mesobrometum erecti’ (Zoller, 1954; Krüsi, 1981) with a species
Vegetation composition by correspondence analysis
A DCA using all data from both sites (Gräte and Grätental) produced two separate groups of relevés which corresponded closely with the two sites, indicating that the sites differed strongly in their species composition. In Grätental, species related to Origanetalia (i.e. thermophilous forest fringe species) attained high cover values (e.g. Seseli libanotis, Origanum vulgare, Fragaria vesca and Thesium bavarum), whereas the vegetation composition of Gräte contained more species characteristic of
Discussion
Experiments such as the one described here are particularly valuable because they provide information about long-term ecological processes which cannot be inferred from the more usual studies of much shorter duration. However, interpretation of results can be made difficult for methodological reasons. For example, there may be changes in recording methods during the course of an experiment, as well as problems of data quality because of the involvement of a large number of observers who may
Acknowledgements
We thank B.R. Kahlert and two anonymous reviewers for helpful comments on the manuscript, C. Bucher for help with English, H. Billing from nature conservation authority Schaffhausen and E. Meister from the Merishausen Council for their permission and support of our study in a nature conservation area. And we thank all those at the Geobotanical Institute who helped to carry out this study. The project was funded by the Swiss Federal Institute of Technology (ETH Zürich; project 41-2710.5).
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