Protected Apes, Unprotected Forest: Composition, Structure and Diversity of Riverine Forest Fragments and Their Conservation Value in Uganda

Abstract

Small forest fragments are common in anthropogenic landscapes in the tropics. These have conservation value if they provide habitat for threatened wildlife and maintain connectivity between larger habitats. Riverine forests have particular 'corridor' potential due to their linear shape, but are under-studied in many regions. We surveyed trees in riverine fragments in Bulindi, an anthropogenic landscape 25 km south of the Budongo Forest in western Uganda, to determine their condition and assess their value for wildlife, particularly endangered chimpanzees Pan troglodytes. We assessed tree composition, structure and diversity and compared results with a previous survey made in Budongo, the nearest main forest block. Riverine fragments were considerably less species-dense and species-rich than Budongo. Community composition differed markedly between sites and there was virtually no overlap in common species. Common trees in fragments were characteristic of East African swamp and groundwater forests (e.g. the palm Phoenix reclinata) and the dominant tree family was the Moraceae, members of which produce fleshy fruits attractive to frugivores (e.g. figs). Important fruit foods for chimpanzees differed between habitats. While basal area of important fruit trees was comparable, overall density was greater in fragments. Our data suggest the riverine fragments offer a relatively food-dense habitat for chimpanzees and other frugivores. Small riverine forests have little or no protection regionally and are being extensively logged and cleared for agriculture. Species logged for timber in Bulindi included important chimpanzee fruit trees. Unless conservation projects successfully reverse current trends, the value of the riverine corridors for maintaining connectivity between main forest blocks is limited.

Wild chimpanzees show group differences in selection of agricultural crops

“…Our current data do not address whether Bulindi and Bossou chimpanzees need to exploit agricultural crops for survival, though this possibility seems more likely at Bulindi given the extent and speed of recent habitat conversion there26. In such circumstances, once a crop food is identified as ‘profitable’, its assimilation into the diet is expected to be faster than in environments where the natural food supply is not being eroded (Figure 4) (cf.…”

“…In chimpanzees marked dietary differences can exist among adjacent or nearby communities1441, attributable in many instances to local variation in flora2642. Nevertheless, differences are not always explained by environmental factors and might instead reflect local feeding traditions or ‘cultures’414344.…”

Forest fragments become farmland: Dietary Response of wild chimpanzees (Pan troglodytes) to fast‐changing anthropogenic landscapes

“…Thus, the chimpanzees continued to have a relatively diverse diet dominated by fruit, despite the loss of most natural forest in their range. McLennan and Plumptre (2012) proposed that a high density of figs, which fruit asynchronously in Bulindi, may help explain the occurrence of chimpanzees in riparian forests regionally. Although figs remained an important dietary component in Period 2, figs appeared in dungs considerably less often and in lesser quantities compared to Period 1 (prediction 3).…”

“…In the 1960s, farmers established shade cocoa gardens within the riparian forest; these were abandoned in the 1970s–1980s, leaving cocoa as a dominant understory tree. Before recent widespread clearance, riparian forests provided a food‐dense habitat for chimpanzees regionally (McLennan & Plumptre, 2012). Rainfall is bimodal with most rain falling between April–May and August–November.…”

Troublesome neighbours: Changing attitudes towards chimpanzees (Pan troglodytes) in a human-dominated landscape in Uganda

“…Important land-use changes have occurred regionally during the last decade: unprotected forests have been extensively logged and cleared for farming (McLennan 2008;McLennan & Plumptre 2012). Human population density in Hoima District was 95.4 individuals per km 2 at the most recent census in 2002 (UBOS 2007).…”