On 8 June at 10:15 Liina Saar will defend her doctoral thesis „Dynamics of grassland plant diversity in changing landscapes“.

Supervisor:
Professor Meelis Pärtel, Ecology and Earth Science, University of Tartu
Senior Research Fellow Aveliina Helm, Ecology and Earth Science, University of Tartu

Opponent:
Professor Robin Pakeman, the James Hutton Institute (Suurbritannia)

Summary:
Over the last century, human-induced changes have influenced considerably biodiversity in grasslands, causing both declines and increases in plant species occurrence and abundance. Ongoing biodiversity decline and anticipated changes in climatic conditions require thorough knowledge of the factors that determine species colonization and extinction dynamics following changes in area and habitat quality.

I studied the processes that drive community assembly in grassland ecosystems at different spatial scales. By comparing the species trait composition of habitats at different successional stages in the same landscape, I was able to detect the vegetation dynamics and the mechanisms behind the changes. My study revealed that at small scales, species with dissimilar traits occurred together in stable grasslands with long grazing regime, whereas species with more similar traits grew together in abandoned grasslands without management and in young developing grasslands, where management activity was started recently. The results suggest the important role of long and stable land-use in the development of grasslands with high biodiversity. I studied which species suffer and benefit most under changing conditions in grasslands by comparing unique vegetation data up to 300 years old to current species lists from the same locations. Analysing re-survey data in Estonian dry calcareous grasslands and grasslands across different parts of Europe, I discovered that ~30% of grassland species had gone locally extinct or showed decreasing occurrence following habitat change. Species more vulnerable to local extinctions had different functional traits and habitat preferences than the more successful species. The losers had good dispersal ability, but poorer ability for local persistence and competition, showing that nutrient enrichment, fragmentation, lack of grazing and mowing and climate change are the main drivers of change in European grasslands.

The results of this thesis led to a better understanding of grassland plant diversity dynamics in changing landscapes. When species’ functional traits are considered, better decisions can be made to mitigate further decline of biodiversity. Research shows that conservation measures also have to focus on species that are still common or have recently been common, as they too are threatened.