Restoration potential of species in the degraded forested sites in Kibale National Park, Uganda.
Omeja, Aria Patrick
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Introduction: Kibale National Park (KNP), like most protected areas in Uganda has had many challenges over the years. In 1971, illegal destruction and encroachment occurred in the game corridor which linked Kibale National Park with Queen Elizabeth National Park, but ended in 1992. Kibale National Park, currently managed by the Uganda Wildlife Authority (UWA), was under the Forest Department before to 1993. One of the management objectives of Forest Department then was sustained production of wood and timber. To achieve this, plantations of exotic tree species were established in 1950 –60s (Osmaston 1959). When UWA took over management of these areas, the management objective changed, and plantations of exotic tree species were clear-felled and the areas left to regenerate naturally. In the southern boundary of the park at Mainaro where elephant grass and Lantana camara had suppressed tree regeneration, intensive reforestation has been undertaken. Since areas of the park are now recovering from historic human impact, there is a need to examine the effectiveness of different management schemes to restore the forest cover. This is a subject that has not been much studied in Kibale or elsewhere, but is required to guide natural forest planning and management, hence, the need for this study. Objectives: The general objective of the study was to evaluate the restoration of woody tree biomass and tree species richness that occur through different land use and management options in Kibale National Park (KNP) and the specific objectives were: (i) To develop a general above ground allometric equation that can be used to calculate overall above ground biomass of standing trees in the disturbed areas of Kibale National Park; (ii) To determine the amount of biomass accumulation and species richness in an abandoned former pine plantation; (iii) To determine the significance of enrichment planting using indigenous tree species after pine plantation establishment and removal; (iv) To evaluate how successful the restoration efforts conducted in Kibale have been, and in comparison to other areas around the tropics; and (v) To find out the most cost efficient approach to promote restoration in the degraded sites in KNP. Methods: Most published allometric relations are typically site-specific, reflecting the original objective for which they were developed (Girgal & Kernik 1984; Pastor et al. 1984) and are not developed for regenerating forest. Since, this study was conducted in an area that was a young regenerating forest, an allometric regression equation of biomass accumulation of woody trees species for this specific area was developed by selecting a sample of early successional trees of varying sizes for harvest and determining their dry weight. This follows methods that rely on the combination of regression equations to produce either species-specific allometry or allometry for groups of species (Jenkins et al. 2003; Keith et al. 1999; Lwanga 2003). Trees in forest lands that were adjacent to the park were identified, and their stem diameter were measured at 0.3 m and 1.3 m above the ground hereafter referred to as diameter at ground height (DGH) and diameter at breast height (DBH) respectively. The trees were then cut and their total lengths measured. Individual trees that were of similar size to those regenerating in the study area (i.e., DBH 1.1 – 10.0 cm and DGH 1.6 – 11.0 cm; within the weights of 0.25 – 10 kg; n = 200) were selected. The choice of tree species for biomass estimation was made based on survey of the vegetation of common tree species in the study area. In total, 200 stems (20 stems per species) were harvested. The species included Albizia grandibracteata Taub., Bridelia micrantha Baill., Celtis africana Burm. f., Celtis durandii Engl., Clausena spp, Maesa lanceolata Forssk., Funtumia latifolia Stapt, Milletia dura Dunn., and Trema orientalis Blume. First, the branches were removed and the total weight of stems and leaves determined. Second, the tree stems were cut into smaller sections and air dried in the laboratory until constant mass was attained. Once all components had reached a constant dry weight, the total weight of the tree was estimated. Findings: The most pressing issue in many regions including Kibale has been the need to assemble information on detailed above ground biomass allometric relationship for the woody tree species on degraded areas. This study has made the first move towards providing such information for this region. The results from this work do not only enhance our understanding of the effects of anthropogenic activities on the forest ecosystem, but also provide much needed information that will facilitate planning, development, and management of forest resources in the degraded areas. It is worth noting that, over the last two decades, there has been a great deal of clearing of forested areas driven by the need for more agricultural land, fuel wood, and building materials for the rapidly expanding human population in the region (Chapman & Chapman, 2003). In 1997, National Environment Management Authority estimated that wood fuel provided 99.2% of energy used for cooking in Kabarole district of Uganda that hosts over 50% of the 795 km2 of KNP. However, comparison of results of the present study and those from Lwanga (2003) and Naughton & Chapman (2002) indicated a significant change in tree species composition and woody tree biomass of KNP, a change that is attributed to a large extent to the recovery of the tree species after disturbance. Other studies within KNP have discovered a number of pits for storing grain and an array of potshards in an area that have traditionally been considered undisturbed forest (Lang Brown and Harrop 1962). It therefore seems likely that in tropical forests, such as Kibale, human activities have altered forest composition for a considerable period of time. Differences in tree biomass and forest composition between areas may reflect the period of time that the area has had to recover from human induced disturbance. However, based on what is known about the life history of the canopy trees in Kibale, distinguishing an area that had been disturbed 1,000 years ago from one that had been disturbed 400 years ago would be a very difficult task. Conclusion: (i) The following allometric equation can be used to estimates the above ground as an indication of forest restoration: y=2.053x + 2.056: (R2 = 0.653, n =200); (ii) Restoration efforts conducted in Kibale and elsewhere around the globe all appear to be successful, based on a long term-time frame. This highlights the resilience of tropical forest systems to recover from disturbance; (iii) Given the three restoration projects evaluated within Kibale, fire protection for 12 years resulted in the biomass accumulation of 2,858 kg/ha/year. The effect of pine establishment and their harvest resulted in the rate of biomass accumulation of between 1,735-2,720 kg/ha/year. The enrichment planting resulted in biomass accumulation of 1,306 kg/ha/year, and fire control after 32 years resulted in the accumulation of 933 kg/ha/year. These amounts of biomass accumulated indicate that the forest is being restored and will play a significant role in atmospheric carbon absorption; (iv) Enrichment planting after pine plantation establishment and removal does not contribute significantly to biomass accumulation, counter to earlier reports presented to UWA. This suggests that UWA should more strongly request that the long-term researchers of Kibale provide data or impressions about future management plans; (v) Given the level of biomass accumulation in the different treatments considered, it can be said that fire protection is the most cost efficient approach to promote restoration in this region and it provides suitable incentives for the involvement of local communities. Recommendations: (i) Both the prevention of fires and the enrichment planting, such as that conducted at Mainaro, appear to provide positive social benefits for the local communities. However, in the future, the research community (anthropologists or sociologists) working in conjunction with UWA and international conservation biologists should evaluate if the benefits to the local communities (e.g., employment) result in more positive impressions of the park by the local community and if this potential positive impression translates into reduced illegal practices conducted by the local community; (ii) Given the extensive cover of Lantana camara, in the restoration compartments in the south of Kibale and its potential to negatively influence restoration in the future, an assessment on the value that L. camara removal would have on tree regeneration should be a priority for future research.