Abstract
Question: Does the role of dispersal and light limitation for community assembly change in temperate semi-natural dry grasslands (SNDGs) post-abandonment?
Location: Temperate calcareous semi-natural dry grasslands, western Estonia (58.642 N, 23.516 E).
Methods: We compared taxonomic and functional community structure of semi-natural dry grasslands in Estonia at two time periods: first in 1975 when traditional grazing prevailed, and again in 2013 when management had ceased for at least 30 yr. In order to assess functional community structure, we used community-weighted mean trait values and mean pair-wise distance as metrics of functional diversity for traits related to plant dispersal and adaptations to reduced light availability. Successional shifts in functional community structure were examined using regression and multivariate analysis.
Results: Changes in community assembly of SNDGs post-abandonment were largely driven by more closed vegetation structure and subsequently reduced light availability, as well as altered availability of dispersal vectors. Importance of long-distance dispersal via grazing animals decreased while importance of bird dispersal increased under abandonment. At the same time, the importance of competition for light increased under abandonment. Results indicate that typical SNDG species are especially susceptible to abandonment because they are light-demanding and depend on dispersal by wind or epizoochory (i.e. on the fur of animals), and their decline likely leads to reduced small-scale species richness.
Conclusions: Vegetation changes in abandoned SNDGs show that regular-management, by creating characteristic light and dispersal conditions, is highly important for maintaining both taxonomic and functional diversity. In particular, typical grassland species might be prone to local extinction as taller vegetation develops post-abandonment. The importance of dispersal processes for community assembly observed in grazed SNDGs thus highlights that successful grassland conservation should include maintenance of dispersal conditions. Grassland conservation should aim to preserve the whole ecosystem and account for the multiple ecosystem processes (e.g. light availability, dispersal), which simultaneously structure plant community composition.