Global circulation models predict an increase in mean annual temperature between 2.1 and 4.6 °C by 2080 in the northern temperate zone. The associated changes in the ratio of extinctions and colonizations at the boundaries of species ranges are expected to result in northward range shifts for a lot of species. However, net species colonization at northern boundary ranges, necessary for a northward shift and for range conservation, may be hampered because of habitat fragmentation. We report the results of two forest plant colonization studies in two fragmented landscapes in central Belgium. Almost all forest plant species (85%) had an extremely low success of colonizing spatially segregated new suitable forest habitats after c. 40 years. In a landscape with higher forest connectivity, colonization success was higher but still insufficient to ensure large‐scale colonization. Under the hypothesis of net extinction at southern range boundaries, forest plant species dispersal limitation will prevent net colonization at northern range boundaries required for range conservation.

Aim The research aimed to investigate how plant species richness of small, fragmented forest patches changes over time. Also interactions between time and area were studied in relation to species richness. Finally, the relative importance of plant dispersal limitation on the process of species accumulation was examined by investigating how species were distributed within a regional landscape.Location Mixed deciduous forest patches in central Belgium. MethodsThe land use history of a region of 80 km 2 was reconstructed using nine historical maps dating from 1775 to 1991. Within a central area of 42 km 2 , 241 forest patches were surveyed for presence/absence of 203 species predominantly occurring in forests. Aggregation of species within this region was estimated using a Monte Carlo simulation. Spatial and temporal patterns of species richness were investigated by both regression and analysis of variance (ANOVA ANOVA).Results Fifty-one of 103 species showed signi®cant spatial aggregation patterns, suggesting severe dispersal limitation. Species richness signi®cantly increased with age. However, the effects of time on species richness could not be separated from area and area and time clearly interacted. Slopes of regression equations for species number on area and patch age were shown to be signi®cantly interrelated.Main conclusions Area and time cannot be treated independently as predictors of plant species richness. Dispersal proved to be important in structuring local forest plant community composition, contrary to most other studies that have investigated local forest plant community structure. The processes of forest succession and species accumulation are controlled by both local and regional processes. More studies focusing on the regional factors determining local community composition are needed in order to fully understand the process of forest plant community assembly.

M. 2003. Influence of environmental and spatial variables on regional distribution of forest plant species in a fragmented and changing landscape. -Ecography 26: 768-776.During the past several centuries, forests in Europe and large parts of North America have been subject to extensive forest clearance. The last several decades, however, numerous new forest patches have been established onto former agricultural land. As a result, the present forest area often consists of a mixture of small forest patches of different age, area, habitat quality and connectivity embedded within a hostile agricultural landscape. In these patchy landscapes, distribution patterns of plant species may be affected by both regional and local factors, although the relative importance of both is still poorly understood. In this study, we investigated distribution patterns of 113 forest plant species in a fragmented landscape. Species abundances at the regional scale conformed to a clearly unimodal abundance distribution which we believe to be related to 1) environmental heterogeneity due to succession and 2) inequality in migration rates. Patch incidence was significantly related to life form, which in turn was correlated to seed mass and dispersal mechanism. Multiple logistic regressions showed that presence/absence of 59 species studied was significantly affected by patch connectivity, patch area and age for 35, 30 and 34 species, respectively. The results of this study indicate that distribution patterns of forest plant species are influenced by both local and regional factors. Moreover, they also demonstrate that next to spatial aspects of fragmentation, temporal patterns of landscape change may have far-reaching effects on presence/absence patterns of plant species and therefore should be incorporated in studies dealing with regional population structures of plants.H. Jacquemyn (hans.jacquemyn@agr.kuleu6en.ac.be), J. Butaye and M. Henry, Lab. for Forest, Nature and Landscape Research, Uni6. of Leu6en, Vital Decosterstraat 102, Belgium.