Delayed and immediate effects of habitat loss on the genetic diversity of the grassland plant Trifolium montanum

Loss of the area and connectivity of natural and semi-natural habitats impose serious negative effects on all aspects of biodiversity. However, quantifying the effect of these pressures is difficult due to the time-lagged responses of biodiversity to landscape change. The aim of this study is to determine if genetic diversity of plant populations exhibits a delayed response to recent landscape change. Using microsatellite markers, we evaluated genetic diversity in 28 populations of a grassland plant Trifolium montanum in Estonian calcareous grasslands. We examined the response of genetic diversity to various current and historic landscape parameters assessed at two time points: (1) 2017, and (2) 1930, when the extent of grasslands in Estonia was at its maximum. Observed heterozygosity (H O ) and inbreeding coefficients (F IS ) were affected by historic grassland availability in the surroundings of the study populations (buffer radius of 2000 m). However, expected heterozygosity (H E ) responded positively to current grassland area and to the availability of grasslands in the surrounding landscape. Allelic richness (A R ) was positively related to current population size. We found evidence for recent genetic bottlenecks in half of the study populations, indicating that landscape change had a negative impact on population demography and consequent genetic diversity. Our findings suggest that regardless of major habitat loss, some measures of genetic diversity of perennial plant species may not be at equilibrium with landscape change. This calls for caution when interpreting observed patterns of plant genetic diversity and requires consideration of historic landscape context when recommending nature conservation strategies.