The Bryophyte Layer In A Calcareous Grassland After A Decade Of Contrasting Mowing Regimes

Analysis of variance and redundancy analysis were used to study the effects of mowing regime and herb Canopy structure oil the bryophyte layer of a calcareous grassland ill southern Belgium. Species richness in mown and control plots did not significantly differ. In control plots, a number of grassland species were able to survive Within a grassy-shrubby fringe 15 years after shrub cutting. This suggests that there might be a time-lag of at least 20 years before cessation of mowing results in a significant decrease in species number per m(2). Mown plots were mostly characterized by the almost complete cover of large pleurocarps. Mowing resulted ill almost continuous herb and moss layers that were unfavourable for a number of annual bryophytes. many of which are of high conservation interest. It Is suggested that grazing, which increases the number of species, especially the number Of pioneers, is likely to be more beneficial to bryophytes. (C) 2003 Elsevier Ltd. All rights reserved

Testing coexistence of extinction debt and colonization credit in fragmented calcareous grasslands with complex historical dynamics

Calcareous grasslands are among the most species-rich ecosystems in temperate countries. However, these ecosystems have suffered from fragmentation and destruction during the last century. We studied the response of calcareous grassland plant diversity to landscape changes in Belgium. Results indicated that high area loss (since 1965) old habitat patches exhibited an extinction debt inverse to low area loss old habitat patches, little depending on the area loss threshold (60%, 70%, 80% or 90%) considered for the distinction between the high and low area loss patches. However, human activities also created new habitat patches in the landscape and therefore provided opportunities for calcareous grassland plant species to colonize new habitats. This also provided opportunities to study species colonization abilities in the context of habitat restoration. We analyzed species richness in new patches compared to old patches in order to detect colonization credit. We detected the presence of a colonization credit in new patches when using high loss old patches (area loss>80%, exhibiting an extinction debt) or all old patches as a reference. However, when the reference was low loss old patches alone (area loss<80%, less likely to exhibit an extinction debt), no colonization credit was detected. In addition, species composition was similar between new patches and old patches. These results are encouraging for restoration programs. However, the results indicated that the presence of an extinction debt in reference habitats could lead to inaccurate conclusions in restoration monitoring. Therefore, extinction debt should be considered when choosing reference habitats to evaluate restoration success