An orchid colonization credit in restored calcareous grasslands
Habitat restoration comprises the re-creation of suitable environmental conditions with the intention of recolonization by certain target species. In previously abandoned calcareous grasslands, however, many characteristic plant species have been reported missing even decades after the reinstatement of traditional mowing or grazing management. Such grasslands are said to exhibit a colonization credit. This may be particularly true for orchid species, which often rely on highly specialized pollination strategies and mycorrhizal associations for completion of their life-cycle. In this study, we investigated whether restored calcareous grasslands exhibited an orchid colonization credit, whether this credit was associated with the degree of grassland fragmentation, and with particular species’ life history traits. Applying the Beals index as a quantitative method to identify suitable habitats, several orchid species were indeed found missing from grasslands deemed suitable. There was no relation, however, between the extent of the colonization credit and the spatial isolation or size of the grasslands. Of all life history traits examined, only a high degree of pollinator specialization could be related to delayed colonization. This may suggest that restoring the pollinator community is an important bottleneck in calcareous grassland restoration.
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