Restorative mowing on semi-natural grasslands: community-level changes and species-level responses
1University of Oulu, Faculty of Science, Department of Biology
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|Persistent link:|| http://urn.fi/urn:isbn:9514259947
|Publish Date:|| 2001-05-15
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kuusamonsali (Auditorium YB210), Linnanmaa, on June 8th, 2001, at 12 noon.
Doctor Thomas E. Juenger
Professor Martin Zobel
This thesis operates at two levels of ecological research, describing the effects of withdrawal and re-introduction of management on grasslands. The aim of the community-level survey was to explore the effects of abandonment, mowing and grazing on semi-natural meadows in northern Finland. At the species level, the aim was to evaluate the responses of three monocarpic meadow species to various degrees of simulated grazing under natural growth conditions.
The community-level studies suggest that strongly competitive grass species with rapid vegetative growth, especially those forming tussocks, are able to retain or increase their cover in abandoned meadows. However, most species are able to persist in a meadow for a long time after abandonment, even when a group of immigrants arrive. This leads to a temporary increase in species diversity, and it may therefore be used as an indicator of ongoing succession. Nevertheless, abandonment is harmful for the rare archaeophytic species in the long run. Late mowing does not have extensive short-term impacts on grass-dominated semi-natural meadows. Therefore, it is neither an efficient nor a substitutional way of management when the goal is to restore a formerly grazed pasture. Mowing executed early in the season may, however, be a more appropriate way of inducing changes in species composition and enhancing species richness.
According to the results of the species-level studies, Erysimum strictum and Rhinanthus minor tolerate well minor apical damage, while more severe damage has a detrimental impact on the performance of both species. The observed differences in regrowth responses between the two species are presumably due to their different habitat requirements in relation to competition. The species-level experiment with two late-flowering populations of field gentian Gentianella campestris ssp. campestris revealed that the southern, Swedish population that has been regularly grazed and mown overcompensated for the intermediate (50%) damage level, whereas the northern, Finnish field gentians growing in unmanaged habitats showed at best partial or full compensation. Regular grazing and mowing have presumably favoured grazing-tolerant plant species, i.e. species with a good regrowth capacity.
Herbivory reshapes grassland plant communities in two ways: directly by affecting the survival and reproductive success of individual plants and indirectly by changing the competitive environment. Tall and competitive perennial species suffer relatively more from damage than true grassland species, i.e. small herbs and grasses, which are better able to tolerate regular tissue losses and respond to damage within the ongoing growing season. As a result, certain species benefit from grazing and mowing in the sense that they may gain more through competitive relaxation than they lose in defoliation.
Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
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