Tree fruiting phenology variations under changing climate: Implications on primate foraging patterns in and around Budongo forest, Uganda

Abstract

Due to observed declines in the number of fruiting trees in Budongo Forest Reserve (BFR), a study was conducted to investigate how the decline in fruiting would affect both primate foraging behaviors in and around BFR, Uganda. The study aimed at investigating the changes in tree fruiting phenology under changing climatic conditions and its implications for primate foraging patterns in and around BFR. It was hypothesized that changes in climate variables (temperature and rainfall) could be the cause of reduced tree fruiting. Tree phenology in different forest compartments was monitored by conducting monthly visits to over 7300 individual trees belonging to 97 tree species out of 465 tree species in BFR to record whether they were fruiting. Primate foraging patterns were explored by observing habituated monkey groups (Cercopithecus mitis, Cercopithecus ascanius and Colobus guereza) to record their dietary composition. Surveys were conducted among forest edge communities to assess the current spatial and temporal crop raiding patterns in relation to past crop raiding patterns. Analysis of phenology patterns showed continued reduction in the number of fruiting trees among different forest compartments. Results further indicate spatial differences in fruiting patterns with more in compartments comprising the primary forest types compared to compartments comprising secondary forest types. Climatic variability had a significant impact on tree fruiting. More fruiting was recorded at the end of rainy season (May) and highest minimum temperatures. Tree fruiting drastically fell and most times trees never fruited when there was no rainfall and temperatures went too high. A comparison of primate foraging patterns indicates that whereas fruits constituted over 60% of primate diet in the early 1990’s, there has been a gradual shift to leaves as main diet (over 45%) In addition, community edge residents (64%) agree that crop raiding around BFR has increased over the last 15 years both in frequency and intensity. It was noted that the reduction and differences in forest tree fruiting directly correlates positively to rainfall, minimum temperature and forest structure. Although reduction in fruiting has led to diet shifts among frugivorous monkeys, fruit availability within the forest seems not to have any impact on crop raiding behaviors of primates. There is thus a need for paradigm shift in management and conservation of BFR. There is also a need for more intense studies on the impacts of changes in tree phenology on other forest ecology components such as herbivores, pollinators, and seed dispersers.