Spatial variability in the vegetation structure and composition of an East African rain forest

• Published in: African journal of ecology 2004-09, Vol.42 (3), p.189-197
• Main Authors: Fashing, Peter J., Mwangi Gathua, J.
• Format: Article
• Language: English
• Subjects: Brillantaisia nitens; Cercopithecus ascanius; disturbance; Kakamega Forest; logging; tropical forest
• ISSN: 0141-6707; 1365-2028
• DOI: 10.1111/j.1365-2028.2004.00512.x

We conducted a study of spatial variation in tree community structure and composition in the Kakamega Forest of western Kenya. We compared the tree communities at two sites, Buyangu and Isecheno, separated by approximately 11 km of contiguous forest. All trees ≥15 cm d.b.h. were censused along transects covering 4.95 ha at Buyangu and 4.15 ha at Isecheno. The structure of the forest at the two sites was similar as mean d.b.h. was comparable and stem size class distribution did not differ significantly. However, species richness and stem density were both much higher at Buyangu. The disparity in stem density may be because of the greater abundance at Isecheno of a semi‐woody undergrowth species, Brillantaisia nitens Lindau, believed to inhibit the establishment of tree seedlings. Floristic composition varied strikingly between sites, with 52% of the species occurring only at one site. Densities of those species present at both sites often differed markedly between sites. Potential sources of these intersite differences in floristic composition include small disparities in rainfall, soil composition, elevation, and temperature as well as past differences in anthropogenic disturbance and in large mammal distribution and abundance. Floristic differences between Buyangu and Isecheno appear to be at least partly responsible for the substantial dietary differences between redtail monkeys (Cercopithecus ascanius Audebert) at these sites. Résumé Nous avons réalisé une étude de la variation spatiale de la structure et de la composition des communautés d'arbres dans la forêt de Kakamega, à l'ouest du Kenya. Nous avons comparé les communautés d'arbres à deux endroits, Buyangu et Isecheno, séparés par ∼11 km de forêt contiguë. Tous les arbres de ≥15 cm de diamètre à hauteur de poitrine (DBH) étaient recensés le long de transects couvrant 4,95 ha à Buyangu et 4,15 ha à Isecheno. La structure de la forêt était semblable aux deux endroits puisque le DBH était comparable et que les classes de distribution par taille des plants n’étaient pas significativement diffèrentes. Cependant, la richesse en espèces et la densité des troncs étaient beaucoup plus élevées à Buyangu. La disparité de densité des troncs pourrait être due à la plus grande abondance à Isecheno d'une espèce semi‐ligneuse de sous‐bois, Brillantesia nitens Lindau, dont on croit qu'elle inhibe l’établissement de jeunes plants d‘arbres. La composition floristique différait étonnamment entre les sites, 52% des esp