Composition of woody species in a dynamic forest-woodland-savannah mosaic in Uganda: implications for conservation and management

Abstract

Abstract. Forest-woodland-savannah mosaics are a common feature in the East African landscape. For the conservation of the woody species that occur in such landscapes, the species patterns and the factors that maintain it need to be understood. We studied the woody species distribution in a forest-woodland-savannah mosaic in Budongo Forest Reserve, Uganda. The existing vegetation gradients were analyzed using data from a total of 591 plots of 400 or 500 m 2 each. Remotely sensed data was used to explore current vegetation cover and the gradients there in for the whole area. A clear species gradient exists in the study area ranging from forest, where there is least disturbance, to wooded grassland, where frequent fire disturbance occurs. Most species are not limited to a specific part of the gradient although many show a maximum abundance at some point along the gradient. Fire and accessibility to the protected area were closely related to variation in species composition along the ordination axis with species like Cynometra alexandri and Uvariopsis congensis occurring at one end of the gradient and Combretum guenzi and Lonchocarpus laxiflorus at the other. The vegetation cover classes identified in the area differed in diversity, density and, especially, basal area. All vegetation cover classes, except open woodland, had indicator species. Diospyros abyssinica, Uvariopsis congensis, Holoptelea grandis and all Celtis species were the indicator species for the forest class, Terminalia velutina and Albizia grandbracteata for closed woodland, Grewia mollis and Combretum mole for very open woodland and Lonchocarpus laxiflorus, Grewia bicolor and Combretum guenzi for the wooded grassland class. Eleven of the species occurred in all cover classes and most of the species that occurred in more than one vegetation cover class showed peak abundance in a specific cover class. Species composition in the study area changes gradually from forest to savannah. Along the gradient, the cover classes are distinguishable in terms of species composition and vegetation structure. These classes are, however, interrelated in species composition. For conservation of the full range of the species within this East African landscape, the mosaic has to be managed as an integrated whole. Burning should be varied over the area with the forest not being burnt at all and the wooded grassland burnt regularly. The different vegetation types that occur between these two extremes should be maintained using a varied fire regime.

The woodland vegetation of the Katavi-Rukwa ecosystem in western Tanzania

“…These numbers are slightly lower than our analysis of the circular plots where we observed an average of 668 trees 2-20 cm dbh/ ha, with and additional 100.7 trees >20 cm dbh/ha. In either case, this stand density is low compared to many dry tropical forest sites (Gentry, 1995;McLaren et al, 2005) but fits well within African savanna or open woodland classifications (White and Hood, 2004;Aerts et al, 2006;Nangendo et al, 2006). Examining patterns in the nearest neighbor analyses we found that adult trees are less spatially clumped than smaller trees (Fig.…”

“…As a consequence, nearly 100% of the landscape, both inside and outside of protected areas is burned each year. This is a very high fire frequency for a dry tropical forest ecosystem and several recent studies have shown that the forest-woodland-grassland complex of much of central Africa is dependent on fire frequency and intensity (Nangendo et al, 2006). Our findings show evidence of such frequent burning with a tree size class structure indicative of continued recruitment within this system (i.e., far more small individuals than larger ones).…”

Mapping East African tropical forests and woodlands — A comparison of classifiers

“…This species composition in turn influences the spectral reflectance of the vegetation in satellite images. In Nangendo et al (2006), this was observed to be the case in Budongo forest. The very open woodland and the wooded grassland classes occurred in sites that were recently burnt, and are probably burnt more often.…”

Forefronting the Socio-Ecological in Savanna Landscapes through Their Spatial and Temporal Contingencies

“…For example, places with the exact same history of composition and configuration of biotic and abiotic components will likely evolve very differently if surrounded by mature forest versus urban development versus agriculture. This kind of neighborhood influence has been expressed as the manifestation of flows of material and energy (as in landscape ecology: [4]), the dispersal of propagules and competitive effects of neighbors (as in plant ecology: [59,60]), spatial autocorrelation (as in geography: [61,62]; as in ecology: [63]), and scale-dependent interconnectedness [37,64] and has been monitored both remotely [65] and with vegetation inventory data [66]. In land cover studies, remotely sensed imagery allows for wall-to-wall classification and mapping of broad areas [67].…”