[en] Destruction and fragmentation of natural and
semi-natural habitats are considered as major
threats for plant species richness. However, the
response of plant species richness to habitat alteration
is sometimes delayed. This delay induces an
extinction debt in plant communities that are thus
prone to undergo species extinctions in the following
years. Several methodologies were proposed
to detect this extinction debt and estimate
the mean number of species yet to disappear. In
this study, we developed a new methodology for
the estimation of the extinction debt extent. Moreover,
we proposed a species approach aimed at
determining which species are more sensitive to
extinction as a consequence of habitat destruction
and fragmentation. Finally, we explored the colonization
ability of habitat specialist species. This
aspect is of fi rst importance to counteract local
species extinctions. Our model habitat is calcareous
grasslands of Southeast Belgium that have
suffered an important fragmentation process since
the beginning of the twentieth century. We estimated
that the mean extinction debt of the calcareous
grassland patches was ca. 24 species, including
ca. six specialist species. We showed that 16
of the 46 specialist species did not meet their area
requirement anymore and were therefore considered
as sensitive to extinction. However, the species
composition of the more recent grasslands
indicates a non-negligible recolonization potential
of specialist species. There is thus a real possibility
to reduce extinction risk by restoring suitable
habitats.
