Grassland Plant Diversity in Relation to Historical and Current Land Use

Gustavsson, E. 2007. Grassland plant diversity in relation to historical and current land use. Doctor's dissertation. About 150 years ago agriculture was drastically reformed and around 90% of the formerly vastly distributed semi-natural grasslands, i.e. unfertilised and uncultivated grasslands, have since then disappeared. Accordingly, grassland plant diversity has declined due to abandonment, changed management methods and habitat loss. Grasslands are species rich as a result of a long management history; the management providing niches for a variety of organisms. Current diversity patterns are thus a result of historical and current land use in combination. This thesis explores some of the connections between historical land use and grassland vascular plants. Two studies concerns the habitat level, i.e. local conditions for grassland plants, two studies the landscape level, i.e. habitat patches in relation to neighbouring patches. In the first study, grassland plant diversity was found to be strongly correlated to 18 th and 19 th century land use, more so than to current land use. Furthermore, the particular sequence by which one land use changed into another from the 18 th century until the mid 20 th century was an important predictor of plant diversity. In the second study, detailed comparison of 18 th century and current grassland management revealed that current grassland management lacks several ecological factors that the literature deems important for grassland plant reproduction. The third and the fourth study explore how plant species richness in specific grasslands is related to the surrounding landscape by studying how current, 19 th and 20 th century grassland connectivity and area are reflected in current species richness of grassland plants. They revealed that the response of grassland plant diversity to different fragmentation components can differ widely between two superficially similar landscapes, although historical components were important in both landscapes for explaining current diversity patterns. Moreover, the direction of livestock movement within the pre-industrial landscape appears to have been an important determinant regarding the functional connectivity between different grassland patches. Given the strong correlation between historical agricultural practices and current plant diversity patterns, this thesis discusses this diversity as a biocultural heritage. The historical aspects of grassland diversity ought to be taken into account in conservation and restoration measures.