Browsing by Author "Ssekuubwa, Enock"

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    Colonization of woody seedlings in the understory of actively and passively restored tropical moist forests Running head: Seedling colonization in afrotropical forests
    (Restoration Ecology, 2019) Ssekuubwa, Enock; Muwanika, Vincent B.; Esaete, Josephine; Tabuti, John R. S.; Tweheyo, Mnason
    The status of woody seedling colonization gives clues about the self-sustainability of restored forests, a tenet of restoration success. Little is known about woody seedling colonization in restored afrotropical forests. We evaluated effects of restoration methods (active vs. passive), sampling year, restoration age and distance from old-growth forests on seedling colonization in restored afrotropical moist forests. Seedlings were measured in 2011 and 2014 in 71 clusters of 284 permanent sampling plots (12.6 m2 each) in actively (initially 3–16 years old) and 21 clusters of 63 plots in passively restored forests (initially 16 years old) in Kibale National Park, western Uganda. Seedlings were also measured in nearby old-growth forests in 3 clusters of 5 plots in 2014. We determined species diversity, richness and abundance per plot, and species composition as measures of seedling colonization in restored and old-growth forests. We found that diversity, richness, and abundance of seedlings were significantly higher in passively than actively restored forests. Diversity and richness, but not abundance significantly increased between sampling years and with restoration age. Distance from old-growth forests did not significantly affect diversity, richness and abundance. Species composition of actively and passively restored forests was different from that of old-growth forests after 19 years since restoration started. Our results show that passive restoration should be the preferred method for recovering afrotropical forests, and highlight the effect of continued management on biodiversity of restored forests.
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    Comparing seed removal rates in actively and passively restored tropical moist forests
    (Restoration Ecology, 2018) Ssekuubwa, Enock; Loe, Leif E.; Sheil, Douglas; Tweheyo, Mnason; Moe, Stein R.
    High rates of seed removal can impede forest recovery, but tropical seed removal studies are few and mainly from the neotropics. Little is known about the comparative influences of active restoration (i.e. planting) and passive restoration (i.e. protection of natural regrowth) on seed removal. We conducted an evaluation of seed removal in grasslands, natural forests (tropical moist semideciduous forest), and actively (21-, 17-, 16-, 11-, 8-, and 6-year-old) and passively (21-year-old) restored forests in Kibale National Park, Uganda. We wanted to compare the effect of vegetation type, time since restoration and restoration actions (i.e. active vs. passive) on removal of seeds of five animal-dispersed tree species during wet and dry seasons. Seeds were either fully exposed or placed in closed mesh cages or under a mesh roof. We used differential removal rates between these treatments to attribute seed removal to different animal taxa. Seed removal rate (percentage of seed removed over a 4-day period) was highest in passively restored forests, compared with actively restored forests, grasslands, and natural forests.We detected no significant relationship between time since restoration and seed removal rates within actively restored sites. Seed removal rate from roofed treatments was not significantly different from removal from open treatments but was significantly higher than removal from closed treatments, which we interpret as reflecting the greater effect of small mammals versus insects. Smaller seeds tended to be removed at a greater rate than larger seeds. We discuss the implications of these findings for forest regeneration.
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    Does restoration success vary with tree size under restoration plantings and regrowth forests?
    (Conservation Science and Practice, 2022) Ssekuubwa, Enock; Goor, Wouter van; Snoep, Martijn; Riemer, Kars; Wanyama, Fredrick; Waiswa, Daniel; Yikii, Fred; Tweheyo, Mnason
    Several studies evaluate active (i.e., seeding/planting) and passive (i.e., protecting forest regrowth) restoration, but few studies examine successional patterns for different plant sizes. By using biodiversity and structure, we examined whether restoration communities approach old-growth forests over time, and whether restoration success varies for different tree sizes in both active and passive interventions. We examined how initial site conditions affect active restoration. Small (dbh ≥ 5 cm), medium (≥15 cm), and large trees (≥30 cm) were measured in 2003–2017 in permanent sample plots in restoration plantings (initially 3–8 years old) and in an old-growth forest in Kibale National Park, Uganda. Trees were also measured in regrowth forests (initially 16 years old) in 2011–2017. We collated information about site conditions from restoration reports. Biodiversity and structure increased over time towards the old-growth forest. Restoration plantings and regrowth forests recovered diversity and structure of small and medium trees except for large trees. Forest recovery increased with proportions of remnant banana plants and shrubs, while isolation from the old-growth forest slowed recovery. Disaggregating vegetation inventory data by tree size may be useful in achieving a holistic measure of restoration. Restorationists could prioritize sites with remnant banana plants and shrubs, and sites closer to old-growth forests in order to achieve better results.
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    Predicting which tropical tree species are vulnerable to forest disturbances
    (African Journal of Ecology, 2017) Babweteera, Fred; Ssekuubwa, Enock
    Tropical forest management often focuses on a few highvalue timber species because they are thought to be the most vulnerable in logged forests. However, other tree species may be vulnerable to secondary effects of logging, like loss of vertebrate dispersers. We examined vulnerability of tree species to loss of vertebrate dispersers in Mabira, a heavily disturbed tropical rainforest in Uganda. Fruit characteristics and shade tolerance regimes of 269 tree species were compiled. Stem densities of tree species producing fruits of various sizes and having different shade tolerance regimes were computed for Mabira and compared with densities of conspecifics in Budongo, a less disturbed forest with similar floral composition. Seventy per cent of tree species in Mabira are animaldispersed, of which 10% are large-fruited light demanders. These species are the most vulnerable because they rarely recruit beneath adult conspecifics and are exclusively dispersed by large vertebrates, also vulnerable in heavily disturbed forests. Comparison of densities between Mabira and Budongo showed that large-fruited light demanders had a lower density in Mabira. Other categories of tree species had similar densities in both forests. It is plausible that the low density of large-fruited light demanders is due to limited recruitment caused by dispersal limitations.
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    Recovery of seedling community attributes during passive restoration of a tropical moist forest in Uganda
    (Applied Vegetation Science, 2021) Ssekuubwa, Enock; Goor, Wouter van; Snoep, Martijn; Riemer, Kars; Wanyama, Fredrick; Tweheyo, Mnason
    There has been a debate about the effectiveness of passive restoration for recovering tropical forests, but few studies quantify the success of passive restoration. The aim of this study was to better understand tropical forest succession under a passive restoration scenario. We compared floristic and functional attributes of seedlings in a passively restored and an old-growth forest, and assessed the effect of restoration age and distance from the old-growth forest on seedling attributes. Location: Kibale National Park, western Uganda. Methods: We measured seedlings in a passively restored and an old-growth forest in 2011, 2014 and 2017. We determined species diversity, structure and composition and searched the literature for functional traits. We used generalized linear mixedeffects models to compare seedling attributes between the restored and old-growth forest and determine the influence of restoration age and distance from the oldgrowth forest. Results: Seedling species abundance, evenness, basal area and height were similar between the restored and old-growth forest. Wood density and abundance of seedlings of different dispersal modes, habitat types, fruit size categories, and regeneration strategies were also similar between the restored and old-growth forest. However, richness, diversity and composition of seedlings were different. We found a positive effect of restoration age on species abundance and abundance of non-zoochorous, medium-fruited, forest-dependent, non-pioneer light demander and shade-tolerant species, and a negative effect on evenness, wood density, abundance of pioneers and compositional dissimilarity. Basal area of seedlings and the abundance of zoochorous and forest-dependent species declined while compositional dissimilarity increased with distance from the old-growth forest. Conclusions: Our results provide empirical evidence on the potential of passive restoration to recover the structure and functionality of tropical forests in a relatively short period of time. We demonstrate that the effect of restoration age and distance from the old-growth forest is not straightforward and depends on the attributes measured.