2005. Effects of landscape structure on the invasive spread of black cherry Prunus serotina in an agriculture landscape in Flanders, Belgium. Á/ Ecography 28: 99 Á/109.Analysing invasive spread from a landscape ecological perspective forms an important challenge in plant invasion ecology. The present study examines the effects of landscape structure on the spatial and temporal dynamics of an expanding black cherry Prunus serotina population within a rural landscape in Flanders, Belgium, carrying a dense network of interconnected hedgerows. The study area, 251 ha in size, harboured a total of 2962 P. serotina individuals. The population was characterised by a negative exponential age distribution, a high growth rate and an early and continuous reproduction throughout the species' life cycle. The historical rate of spread of the species through the hedgerow network progressively increased with time, especially during the last decade. Spatial point pattern analysis revealed that the individuals had a significantly clustered distribution pattern and were spatially aggregated around seed sources, hedgerow intersections and roosting trees. Logistic regression analysis confirmed the effect of landscape structure on P. serotina occurrence, suggesting directional long distance dispersal by avian dispersal vectors, resulting in a differential seed pressure throughout the hedgerow network due to the preference of dispersing birds for roosting in structurally rich hedgerow with large trees near hedgerow intersections. Hence, the distribution of P. serotina in agricultural landscapes was strongly mediated by dispersal processes. Furthermore, decreasing spatial aggregation along the species life cycle, with especially seedlings and saplings being significantly aggregated while adult individuals were mostly distributed at random, and a relative outward shift of seedling recruitment curves with time indicate density dependent mortality, probably caused by intraspecific competition. B. Deckers

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Although seed dispersal is considered to be a key process determining the spatial structure and spread of non-native plant populations, few studies have explicitly addressed the link between dispersal vector behaviour, seed distribution and seedling recruitment to gain insight into the process of exotic species invasion within a fragmented landscape context. The present study analyses the relationship between avian frugivory and spatial patterns of seed deposition and seedling recruitment for an expanding population of the invasive Prunus serotina in a hedgerow network landscape in Flanders, Belgium. We quantified fruit production, observed frugivores, and determined the spatial distribution of bird droppings and P. serotina seedlings. A relatively diverse assemblage of frugivores visited P. serotina seed trees, with Columba palumbus and Turdus merula being by far the most important dispersers. Landscape structure strongly affected dispersal vector behaviour and the spatial distribution of perching birds, droppings and seedlings. Frugivorous birds non-randomly dispersed seeds to perching sites and an association between perching birds, seed deposition and seedling recruitment was found. Results indicate that landscape structure contributes to nonrandom seed deposition of P. serotina by common local frugivores. Cutting the larger seed trees is proposed as the most feasible measure to slow down the invasion rate.

Although the importance of hedgerows for sustainable agriculture and conservation of rural biodiversity is increasingly being recognized, obtaining insight into the spatial and temporal dynamics of hedgerow networks remains an important challenge for landscape ecologists, with the key factors driving changes in rural landscape structure especially deserving further attention. The present study analyses the long-term history of a hedgerow network landscape in Flanders, Belgium. A detailed reconstruction of the hedgerow network is made at five points in time, starting at the end of the 18th century until present, for 367 distinct 400 m×400 m samples. Whilst hedgerows were mainly concentrated around historical village centres and within valleys at the end of 18th century, the network expanded progressively during the 19th century. In the 20th century, the hedgerow network degraded strongly, with hedgerow density and connectivity declining and mesh-size heterogeneity and network fragmentation increasing, although the network recovered slightly during the 1990s. Different trajectories of change in hedgerow network structure were observed depending on landscape position, with both topography and village proximity significantly affecting hedgerow network dynamics. The present network structure was mainly governed by land use, with highly developed networks being predominantly associated with pasture. Three main conclusions arise from the results of this study. First, the role of land use and landscape position as basic factors steering hedgerow network dynamics at the landscape scale is demonstrated. Second, the long-term perspective of the study enabled insight into the poorly known expansion phase of hedgerow networks, linked mainly with the development of small-scale labour-intensive agriculture. Finally, the findings confirm the large-scale degradation of linear semi-natural habitats in European agricultural landscapes during most of the 20th century, and indicate that a pro-active rural policy can halt and even reverse this process.