The fate of grassland species in the modern changing landscape: Effects of management on vegetation and population dynamics in road verges and pastures
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AbstractThis thesis presents a study of vegetation and plant population dynamics in a local vegetation–environment context, and examines the importance of management regimes for the maintenance of grassland species. In the modern, changing landscape, semi-natural grasslands are declining, followed by changes in species composition and a huge biodiversity loss at regional as well as international level. Moreover, the remaining grasslands often receive different manage¬ment than the traditional regime. ‘Novel’ grasslands like road verges, on the other hand, steadily increase, and they have been suggested as refuges for declining grassland species, given appropriate management.
I surveyed the vegetation–environment relationships of aboveground vegetation and seed bank. Moreover, I studied management effects on vegetation dynamics as well as on population dynamics of Pimpinella saxifraga. This low-growing perennial species is considered an indicator of semi-natural grasslands.
Road verges and pastures shared many species. The aboveground vegetation varied gradually along the most important gradient; the management history, whereas other significant environmental factors did not separate the two habitats. The seed bank response to environmental factors resembled the response in aboveground vegetation, but at a coarser scale. For both aboveground vegetation and seed bank, I found that the environmental relationships depended on the scale of observation. The ambiguous effect of management and lack of directional change in species composition indicated considerable resistance to changes in management. The vegetation’s large proportion of perennial species may on one hand have contributed to fine scale dynamics, but their long life span probably slowed down the vegetation dynamics, in our study reinforced by high drought frequency acting as a resetting mechanism for succession. The study of P. saxifraga population dynamics revealed that consider¬able management effects were buffered through life-history trade-offs. The present road verge management prevented seedling production, but the species nevertheless managed relatively well, due to the ‘mosaic’ management of the road verges (ranging from twice cutting via one cutting to no cutting in different distances from the road bed). This spatially fine-scaled variation in management generated a trade-off between fertility and survival, thus creating source-sink dynamics for the species. This exemplifies the unique potential of this novel ecosystem to maintain semi-natural grassland species.
List of papers
|I. Auestad, I., Rydgren, K. & Økland, R.H. (2008) Scale-dependence of vegetationenvironment relationships in semi-natural grasslands. Journal of Vegetation Science 19: 139-148. The paper is not available in DUO. The published version is available at: https://doi.org/10.3170/2007-8-18344|
|II. Auestad, I. & Rydgren, K. Soil seed banks: echoes of the aboveground vegetation? Manuscript. The paper is not available in DUO.|
|III. Auestad, I., Rydgren, K. & Austad, I. High resistance in grassland vegetation prohibits management response. Manuscript. The paper is not available in DUO.|
|IV. Auestad, I., Rydgren, K. & de Kroon, H. Pimpinella saxifraga is maintained in road verges by mosaic management. Manuscript. The paper is not available in DUO.|