Browsing by Author "Witkowski, T.F."

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    Population structure and regeneration of multiple-use tree species in a semi-deciduous African tropical rainforest: Implications for primate conservation
    (Forest Ecology and Management, 2009) Mwavua, Edward N.; Witkowski, T.F.
    The conservation of threatened frugivorous primates (e.g. chimpanzees) and birds in the Albertine Rift Ecoregion rainforests requires the conservation of food tree species aided by an understanding of their natural regeneration and population trends. However, little is known of the population structure and regeneration patterns of a wide range of multiple-use tree species in many of these forests. We examined the population structures and regeneration patterns of 15 tree species (including pioneer, non-pioneer and shade-bearers) that are both timber and primate food sources in Budongo Forest Reserve, NW Uganda, by constructing species population size-class distributions (SCDs), and calculating SCD slopes, seedling:juvenile and juvenile:adult ratios. The SCD slopes were used as indicators of population structure, while the slope values were used to summarise, in a single number, the shape of the SCD for a species. Species composition between forest communities varied significantly, suggesting the influence of spatial environmental variations. Nine species had significant positive correlations between seedling and adult densities. Nine species, namely Lasiodiscus mildbraedii, Celtis mildbraedii, Pouteria altissima, Chrysophyllum albidum, Cynometra alexandri, Diospyros abyssinica, Funtumia elastica, Chrysophyllum perpulchrum and Antiaris toxicaria had highly negative SCD slopes spanning 2.47 to 1.1, and juvenile:adult ratios spanning from 5.34 to 1.62. Hence, clearly exhibiting ‘inverse J’ type curves, and suggesting a successful or healthy regeneration pattern. In contrast, both Alstonia boonei and Cordia millenii had weakly negative SCD slopes of 0.25, and juvenile:adult ratios <1; hence a pulsed or discontinuous regeneration pattern and low recruitment. The SCD slopes and juvenile:adult ratios varied between forest communities and historical management practices (HMPs). Most species recruit successfully and continuously over time, and hence have a more stable population structure. However, a discontinuous regeneration pattern for some, reflects unsustainable harvesting, that potentially eliminates seed sources for future generations. Hence, management of the Budongo Forest Reserve requires plans/practices that will enhance and facilitate the recruitment of both the vigorously and poorly regenerating species to ensure sustainable forest development. Preserving some fruiting trees in logged areas will benefit both long-term sustainable timber production and wildlife conservation, by providing food for frugivorous animals that will disperse the seeds.
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    Sprouting of woody species following cutting and tree-fall in a lowland semi-deciduous tropical rainforest, North-Western Uganda
    (Forest Ecology and Management, 2008) Mwavu, Edward N.; Witkowski, T.F.
    Effective management, conservation and restoration of tropical forests require an understanding of plant responses (e.g. sprouting) to natural and anthropogenic disturbance events. Sprouting among woody plants within Budongo Forest Reserve (BFR) in response to harvesting for poles and saplings, and tree and branch fall disturbances was examined. A total of 835 woody stumps representing 122 species were recorded. Human harvesting accounted for 83% of 835 damaged stumps. Both canopy and sub-canopy trees sprouted prolifically. Of the 122 affected species, 119 (97.5%) from 31 families sprouted from stem stumps, with only Caloncoba crepiniana exhibiting stem and root sprouting. Only Maesopsis eminii, Cordia milleni and Raphia farinifera did not resprout. Sprouts/stump ranged from 16.3 1.8 (S.E.) for Rawsonia lucida, to 1 for 10 species. Number of sprouts/stump differed significantly among families (Kruskal–Wallis H = 182.63, P < 0.0001), species (H = 256.26, P < 0.0001) and stump size-classes (H = 73.18, P < 0.0001). Mean sprouts/stump was significantly higher for intermediate sized stems of basal diameter (BD) 5.1– 20.0 cm. Dead sprouts occurred on 26 species. There were species-specific significant differences in height (H = 39.92, P = 0.0297) and BD (H = 52.34, P = 0.0011) of the leading sprout. Stump BD (x21 ¼ 6:62, P = 0.0101), height (x21 ¼ 38:52, P < 0.0001), bark-thickness (x21 ¼ 14:56, P < 0.0001) and height of stump above ground at which the first sprout emerged (x21 ¼ 74:42, P < 0.0001) were significant predictors of sprouting ability among individuals. Hence, this semi-deciduous tropical rainforest has a high proportion of sprouting species and incidence of sprouting stems. Sprouting of small and relatively large stumps, and the survival and growth of sprouts, suggests that sprouting plays an important role in forest resilience to selective timber, pole and sapling harvesting.