Height-diameter allometry and above ground biomass in tropical montane forests: Insights from the Albertine Rift in Africa

Tropical montane forests provide an important natural laboratory to test ecological theory. While it is well-known that some aspects of forest structure change with altitude, little is known on the effects of altitude on above ground biomass (AGB), particularly with regard to changing height-diameter allometry. To address this we investigate (1) the effects of altitude on height-diameter allometry, (2) how different height-diameter allometric models affect above ground biomass estimates; and (3) how other forest structural, taxonomic and environmental attributes affect above ground biomass using 30 permanent sample plots (1-ha; all trees ≥ 10 cm diameter measured) established between 1250 and 2600 m asl in Kahuzi Biega National Park in eastern Democratic Republic of Congo. Forest structure and species composition differed with increasing altitude, with four forest types identified. Different height-diameter allometric models performed better with the different forest types, as trees got smaller with increasing altitude. Above ground biomass ranged from 168 to 290 Mg ha-1, but there were no significant differences in AGB between forests types, as tree size decreased but stem density increased with increasing altitude. Forest structure had greater effects on above ground biomass than forest diversity. Soil attributes (K and acidity, pH) also significantly affected above ground biomass. Results show how forest structural, taxonomic and environmental attributes affect above ground biomass in African tropical montane forests. They particularly highlight that the use of regional height-diameter models introduces significant biases in above ground biomass estimates, and that different height-diameter models might be preferred for different forest types, and these should be considered in future studies

Contribution of Wetlands to Household Income and Food Security in the Nyumba Ya Mungu Wetland System, Northern Tanzania

Wetlands ecosystems are diverse and have diverse ecological, environmental, socioeconomic and cultural values that have not been fully quantified in Tanzania. This study was conducted to quantify the  contribution of wetlands to socio-economic well being of the local communities adjacent to the ‘Nyumba ya Mungu’ wetland system in Kilimanjaro region Tanzania. Specifically the study assessed the contribution of wetland system to household income and food security and problems associated with the utilization of the wetland. Both primary and secondary data were used. Primary data were collected by use of structured questionnaire administered to different households whose income and  food depend mainly on this wetland system. Secondary data were obtained from published and unpublished reports from various sources. Participant observation was used to supplement information from questionnaires. Data collected was analyzed using Statistical Package for Social Science (SPSS). Results indicate that about 92% and 95% of the households derive their income and food from the wetland resources respectively. Main products of socio-economic values at the ‘Nyumba ya Mungu’ wetlands are fish (71%), water (19%), roofing materials (6%) and vegetables (4%). Activities related to the presence of the wetland are fishing (52%), fish gutting (10%), fish business (29%), boat hiring (3%) and farming (6%). On average about 94% of the local community around ‘Nyumba ya Mungu’ wetland depend entirely on the dam for their income and food. Absence or degradation of the wetland may imply high costs to the society/government in providing the products and/or services that would be foregone. Environmental costs associated with alternative options that would be practiced by the community in sourcing out the missing products and services would also be high. With increasing population around the wetlands there is a need to design alternative income generating activities to reduce overexploitation and degradation of the wetland. Integrated approach in designing wise use/wetland friendly activities can be useful in sustainable management of the wetlands.Key words: Wetlands, household, income, food security, fishing

The Role Of Urban Forestry In Mitigating Climate Change And Performing Environmental Services In Tanzania

The possibility of global climate change, due to increasing levels of CO2 concentrations is one of the key environmental concerns today, and the role of terrestrial vegetation management has received attention as a means of mitigating carbon emissions and climate change. In this study tree dimensions and assessment of plant species composition were used to quantify the potential of urban ecosystems in acting as carbon sink and mitigating climate change through carbon assimilation and storage and the potential of the system to enhance biodiversity conservation taking Morogoro Municipality as a case study. Biomass/carbon models for trees were developed and used to predict biomass/carbon storage based on tree diameters. The model was in the form B = 0.5927DBH1.8316 (r2 =0.91, P< 0.01). The carbon content was computed as 50% of the tree biomass. The tree carbon for Morogoro municipality ranged from 4.63±3.39 to 21.18±12.41t km-1 length of ground surface along roads and avenues. Newly established areas seemed to have lower carbon storage potential while areas established earlier have highest carbon storage potential. About 36 different tree species growing/planted in the Morogoro municipal were identified, dominated by Senna siamea, Azadirachta indica, Polyalthia longifolia, Leucaena leucocephala, Pithecelobium dulce and Mangifera indica. Apart from being natural amenity the tree species also act as CO2 sink through photosynthesis and areas of ex-situ conservation of plant diversity. Urban forestry can store large amount of carbon in addition to biodiversity conservation especially where they cover extensive areas like parks, gardens and avenues managed over long periods, as is the case in urban ecosystems. Improved management of urban forests will likely improve the potential for carbon storage by terrestrial vegetation as a means of mitigating CO2 emissions and climate change as well as biodiversity conservation. Keywords: Urban forestry - carbon emission - mitigation options - carbon sequestration - Biomass.Tanzania Journal of Forestry and Nature Conservation Vol. 77 2008: pp. 25-3