Myriam Dumortier

Predicting vascular plant species richness of fragmented forests in agricultural landscapes in central Belgium

This paper tests different methods to assess the species richness of vascular plants in fragmented forests embedded in agricultural landscapes. Certain plant species enabled us to rank forest patches in order of actual species richness, but failed to predict the exact number of plant species. However, the exact species richness could be satisfactorily predicted through multiple linear regression models that used a series of environmental variables (69% explained variance). Using this method, species richness was easier to predict in forests on alluvial soil and of young age (77 and 66% explained variance, respectively) than in those on non-alluvial soil and of old age (47 and 50% explained variance, respectively). The latter needed more observations (improvement to 70 and 56% explained variance, respectively) or more variables (improvement to 61 and 73% explained variance, respectively) to develop a reliable model. Predictions based on data obtained using GIS were satisfactory only for forests on alluvial soil (58% explained variance). Important indicators of species-rich forests were habitat diversity, forest age and forest area. Species richness was substantially larger in forests on alluvial soil compared with those on non-alluvial soil. Lower phosphorus availability to plants and proximity to older forests indicated a higher species richness in forests on alluvial soil and of young age. A higher pH and a lower C/N-ratio of soil indicated a higher species richness in forests on non-alluvial soil and of old age. It is thus possible to predict species richness of vascular plants in different types of forest using environmental variables, which is useful when selecting and managing forests for biodiversity conservation and restoration.

Effects of age and distance on the composition of mixed deciduous forest fragments in an agricultural landscape

Forest patches in central Belgium were inventoried twice for the presence or absence of forest plant species to study the effects of age and distance on species composition. All forests in the study area were subdivided based on their land use history. To avoid effects of autocorrelated environ- mental characteristics on species composition, habitat homo- geneity was indirectly investigated using a TWINSPAN clas- sification of the vegetation data. Two major habitats (alluvial and non-alluvial forests) were distinguished and analysed separately. Patterns of species composition were investigated at the landscape level using Mantel tests. Species composition similarity measures were calculated between all pairs of frag- ments based on the floristic data. A highly significant correla- tion was found between species composition similarity and inter-patch distance. Difference in age, which we used as a measure for habitat quality, was less important in explaining species composition patterns. The effects of spatial configura- tion became significant when difference in age was accounted for, and a partial correlation was calculated between inter- patch distance and species composition similarity. Different results were found for alluvial and non-alluvial forest types. Alluvial forests were more influenced by the spatial configu- ration than the non-alluvial. For the non-alluvial forest type effects measured with the difference in age between forest fragments obscured the effects of inter-patch distance. Based on our findings we suggest that species composition is not only internally generated, but external processes such as dif- ferential colonization caused by varying degrees of isolation may be of overriding importance.

Effects of harvesting dates and frequencies on above and below-ground dynamics in Belgian wet grasslands

A trial was established to assess the effects of harvesting dates and frequencies on the species, biomass and nutrient dynamics in wet grasslands in Belgium. Above and below-ground developments wer...