The impact of past land-use change on floristic diversity in southern Sweden : a quantitative approach based on high-resolution pollen data
This thesis explores the relationship between land-use and floristic diversity over the last three millennia in the uplands of southern Sweden. A quantitative approach based on high-resolution pollen data was applied, using the Landscape Reconstruction Algorithm (LRA), historical maps/aerial photographs, palynological richness and new ways to estimate past evenness at regional and local spatial scales, which enable estimates of the rate and degree of change in land-use and floristic diversity. The results show that agricultural land-use was most widespread AD 350-1850 at a regional scale, and a period of land-use expansion followed by regression AD 350-750 was identified. The land-use patterns were similar around the local study sites, with agricultural expansion during the 13th century, partly abandoned landscape around AD 1400, re-establishment during the 15-16th century and a transition from traditional to modern land-use during the 20th century. Palynological richness responds within 20 to 80 years during agricultural expansion and regression both at regional and local scales, which provides quantitative estimates of the ecosystem resilience to land-use changes. During succession from open land to more tree covered habitats, floristic richness may increase temporarily during c. 40 years. The REVEALS and LOVE-based evenness introduced in this thesis reflects changes in landscape composition and the extent of available habitats. The more widespread agriculture from the 13th to 19th century was of substantial importance for achieving the high floristic diversity that characterizes the traditional landscape, which can allow species favoured by traditional management, succession and woodlands to coexist. The modern landscape is unusual in a centennial to millennial perspective with more habitats related to coniferous woods and fewer habitats related to deciduous trees and open land taxa, which may not be sustainable to preserve floristic diversity in the future. This thesis provides some examples of long-term (decadal to millennial scale) impacts of land-use changes on floristic diversity at regional and local scales, and the adopted approach is potentially a useful tool for conservation strategies when planning management within specific areas.
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