Destruction and fragmentation of (semi-) natural habitats are considered the main causes of biodiversity loss worldwide. Plant species may exhibit a slow response to fragmentation, resulting in the development of an extinction debt in fragmented plant communities. The detection of extinction debt is of primary importance in habitat conservation strategies. We applied two different approaches proposed in the literature to identify extinction debt in Southeast Belgium calcareous grasslands. The first method compared species richness between stable and fragmented habitat patches. The second explored correlations between current species richness and current and past landscape configurations using multiple regression analyses. We subsequently examined results generated by both methods. In addition, we proposed techniques to identify species that are more likely to support extinction debt and associated functional traits. We estimated a respective extinction debt of approximately 28% and 35% of the total and specialist species richness. Similar results were obtained from both methods. We identified 15 threatened specialist species under the current landscape configuration. It is likely the landscape configuration no longer supports the species habitat requirements. We demonstrated that non-clonal species are most threatened, as well as taxa that cannot persist in degraded habitats and form only sparsely distributed populations. We discussed our results in light of other studies in similar habitats, and the overall implications for habitat conservation.
Calcareous grasslands have long been recognized as biodiversity hotspots in Europe.However, in recent decades these ecosystems have seen rapid decline. In Belgium, more than 100 ha of calcareous grasslands have been restored from oak coppices and pine forests since the 1990s. The aim of the present study was to provide a quantitative assessment of the success of these restoration efforts, using two sets of indicators: one related to soil conditions, the other related to vascular plant communities. Soil conditions were evaluated by comparing soil samples from pre-restoration forest stands, restored grasslands (3 age classes: 2-4 years; 5-8 years, 10-15 years) and reference grasslands. The analysis revealed no significant differences in soil N, P and K contents between pre-restoration forests and restored and reference grasslands. We observed a decrease in the mineralization rate indicators in both pre-restoration forests and recent grassland restorations, which was resorbed in older restorations. Floristic surveys revealed that plant species composition of older restorations was most like reference grasslands. However, some differences in species composition persisted after 15 years.Moreover, a few rare species did not colonise restored grasslands despite a close seed source.Non-recolonization by a set of species expected on calcareous grasslands may be due to dispersal limitation and higher cover by native invasive grasses in restored parcels. These results were discussed in term of implications for management.
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