LAUSR

Aims There is a time lag between loss of semi-natural grassland and a reduction of population size that leads to the extinction of grassland plant specialists; thus, current species richness in the grassland may include an ‘extinction debt’. However, previous studies have not tried to detect the presence of an extinction debt from individual species loss and colonization rates in an assemblage of plant species. In addition, few researchers have studied extinction debt using factors other than landscape changes [e.g. the impacts of management (mowing or burning), habitat use by large herbivores or climate factors]. In the present study, we examined an extinction debt for vascular plant species by monitoring their survival and colonization dynamics. Location Abandoned and managed semi-natural grasslands, central Japan, where the area of grasslands has decreased considerably. Methods We re-surveyed species compositions in the 2000s in plots that had been surveyed in the 1980s, and estimated the impacts of the past (1910s) and recent (1980s–2000s) proportion of the total grassland area and the abovementioned factors on species dynamics during the past 20 yrs using hierarchical Bayesian models. Results In abandoned grasslands, the past grassland proportion was significantly positively associated with the probabilities of survival of 96% of the grassland specialists and of colonization by 21% of these specialists. The effects of the past grassland proportion on the specialists were much stronger than those of recent grassland proportion and the other factors studied (i.e. herbivores, climate). In managed grasslands, however, the past grassland proportion had little effect on survival of and colonization by specialists from the result that few specialists were significantly affected by past grassland proportion. Conclusions We found higher probabilities of both survival of and colonization by grassland specialists at sites with larger past habitat areas, which suggests that there is a time lag after habitat loss before the loss of specialists. In addition, we found that continuous management inhibits payment of the extinction debt created by the habitat loss.