K J Koffi

Fragmentation of Forest Landscapes in Central Africa: Causes, Consequences and Management

Forest fragmentation has a paramount impact on landscape pattern and has therefore been a key focus of landscape ecology. Trends and causes of deforestation are analysed for the Democratic Republic of the Congo, Rwanda and Burundi, and are put in a regional, continental and global perspective. In order to investigate the role of shifting cultivation as a driver of fragmentation, the dynamics of a forest landscape between 1970 and 2005 for a study area in the Bas-Congo province of the Democratic Republic of the Congo were analysed. Using a transition matrix and the identification of the spatial land transformation processes involved, historical data are compared with the current situation based upon field visits and remote sensing imagery. As a consequence of non sustainable shifting agriculture, forest fragmentation is observed, leading to an expansion of savannah, fallow lands and fields which replace secondary forest vegetation and limit forest succession towards primary forest. Since forest ecosystems are known to be the habitat of indicator species only observed in one specific phytogeographic territory, the potential impact of habitat preservation for these species is investigated. A dataset of 310 Acanthaceae species containing 6362 herbarium samples for the Democratic Republic of the Congo, Rwanda and Burundi is analysed and species presence is compared with the phytogeographic theories of Robyns (1948), White (1979,1983) and Ndjele (1988). Study of the spatial distribution and analyses of species habitats reveal the importance of forest preservation to protect these indicator species. Conservation of these habitats should therefore be given priority to avoid loss of genetic resources for future generations. Implications for the management of forested landscapes are discussed, regarding the role of local populations, the application of ecological principles, the conservation of virgin forests, the potential role of forest plantations, and the importance of landscape pattern analysis.

Spatial pattern analysis as a focus of landscape ecology to support evaluation of human impact on landscapes and diversity

The relation between landscape patterns and ecological processes forms a central hypothesis of landscape ecology. Three types of pattern analysis to assess anthropogenic impacts on landscape ecosystems and biodiversity are presented in this chapter. Firstly, the results of an analysis of Acanthaceae data in Central Africa are presented and compared with phytogeographic theories. Phytogeography data reflect the spatial variability of plant diversity, and constitute therefore a major tool in conservation policy development. We investigated if it was possible to proxy the phytogeographic classifications by the spatial distribution of Acanthaceae only. When combined with a classic landscape pattern analysis, this type of study could provide complementary information for the definition of conservation priorities. Secondly, we present an analysis of periodic vegetations in the Sudan. It can be accepted that through an understanding of the underlying mechanisms of the formation of this unique pattern geometry, the knowledge with regard to the functioning and vulnerability of these ecosystems can be deepened. Using high-resolution remote sensing imagery and digital elevation models, the relation between pattern symmetry and slope gradient was explored. In particular, slope gradients that could condition the transition between spotted and tiger bush pattern types were focused. The influence of other sources of anisotropy was also considered. Finally, a complementary approach to the calculation of landscape metrics to analyse landscape pattern is described, using the spatial processes themselves causing landscape transformation. Landscape ecologists agree that there appears to be a limited number of common spatial configurations that can result from land transformation processes. Ten processes of landscape transformation are considered: aggregation, attrition, creation, deformation, dissection, enlargement, fragmentation, perforation, shift, and shrinkage. A decision tree is presented that enables definition of the transformation process involved using patch-based data. This technique can help landscape managers to refine their description of landscape dynamics and will assist them in identifying the drivers of landscape transformation