The role of the Miombo woodlands of the Southern highlands of Tanzania as carbon sinks

Inventory and monitoring of existing carbon pools in ecosystems is important for establishment of baselines for Reduced Emissions from Deforestation and Forest Degradation (REDD) as well as understanding the global carbon budget. We used tree dimensions to quantify the carbon pools of two sites in Miombo woodlands of the Southern Highlands of Tanzania. Mean above ground carbon density of the Miombo ecosystem was 19.2t ha-1. Of the total carbon, 40 and 60% was contributed by stems and branches respectively. Different species contributed differently to carbon stocks in these ecosystems with Brachystegia spiciformis and Julbernardia globiflora contributing the most. The estimated carbon stocks in this ecosystem is within the range observed in dry forests elsewhere though they are in their early stages of regeneration after extensive exploitation pressure. Under proper management there is a tremendous capacity for carbon storage in these Miombo woodlands to mitigate carbon emissions. Since Miombo species tend to invest much in roots an assessment of below ground carbon in roots can add to the carbon storage potential of these ecosystems. Evaluation of the root and soil carbon in these ecosystems is important in determining the full potential of these ecosystems to act as carbon sink.Non

Measuring and modelling above-ground carbon and tree allometry along a tropical elevation gradient

Emerging international policy aimed at reducing carbon emissions from deforestation and forest degradation (REDD+) in developing countries, has resulted in numerous studies on above-ground live carbon (AGC) in tropical forests. However, few studies have addressed the relative importance of disturbance, topography, climate, soil and methods for stem measurement, on the estimation of AGC, or the costs of improving AGC estimates by altering sample regimes. We established 18 one hectare plots containing 7201 stems, stratified along forested elevation gradients in Tanzania. We recorded a broad set of physical, climatic and edaphic predictors of AGC and tree stature. AGC estimates using stem diameter, height and wood density, gave a mean value of 174.6 t ha−1, compared with 229.6 t ha−1 when height was excluded. Regression models revealed that stems were tallest for a given diameter at mid-elevation (1000–1250 m), on south-facing slopes, and without past logging. High AGC was strongly associated with shallow slopes, followed by intermediate elevation, elephant absence, low potential evapotranspiration and low soil pH. Further regression models to investigate the structural habitat features associated with AGC, revealed significant positive influence of basal area, stem density, and height:diameter ratio, rather than the mean wood density of species present. Large stems (⩾70 cm dbh; 4.6% of stems) contained 52% of AGC in all plots, declining to 36% in lowland plots. We discuss the cost:benefit of different measurements and recommend a tiered approach to AGC monitoring, depending on available resources. AGC assessments in African forests could exclude small stems, but should aim to record disturbance, topography and species. Stem height is vital for AGC estimation and valuation; when excluding height our 55 t ha−1 over-estimation of AGC would have over-valued the carbon resource by 24% (US$3300 ha−1)