Estimation of tree removals in Miombo woodlands of mainland Tanzania

PhD Thesis

Miombo woodlands are major vegetation type covering about 93% of the forest land of Mainland Tanzania. It forms an integral part of the rural landscape in Tanzania and plays a crucial role in providing a wide range of goods and services including carbon sequestration. However, the sustainability of miombo woodlands resources depend on the balance between increment/growth rate and the magnitude of utilization. While many studies have been conducted to evaluate growth rate/increment little has been done to evaluate tree removals in miombo woodlands of mainland Tanzania. Quantification of volume, biomass, and carbon stocks removals is vital in developing effective climate change mitigation strategies, decision making, and promoting sustainable forest management.The overall objective of this study was to assess volume and carbon removals in miombo woodlands of mainland Tanzania as a result of tree cutting. Specifically, the present study intended to: 1), develop biomass and volume models based on stump diameter for assessing forest removals; 2) estimate volume and carbon stocks removals as a result of tree cutting; 3) examine drivers of removals and their influences on aboveground carbon removals in miombo woodlands and 4) estimate volume loss due to extra stump height in miombo woodlands of mainland Tanzania. To this end, two main data sets were used. The first is composed of field data collected from miombo woodlands located in three regions i.e. Manyara, Tabora and Lindi. The data were used for developing individual tree biomass and volume models essential for estimating biomass and volume removals directly from stump diameter (SD). Estimating volume and biomass directly from SD has an advantage of reducing the accumulated errors that could results from estimation of diameter at breast height (DBH) of the removed tree and used the estimated DBH to estimate volume and biomass from available equation that utilize the estimated DBH. The second is stumps data (diameter and height) collected during the implementation of the Tanzania National Forest Resources Monitoring and Assessment (NAFORMA). This data set were requested from Tanzania Forest Services agency (TFS), Tanzania Forestry Research Institute (TAFORI), and Sokoine University of Agriculture through the National Carbon Monitoring Centre (NCMC).This data set were used to respond to the objective two, three and four of this study. All the data were analysed in R software. Results revealed that, in all the models developed, SD explained over 70% of the variations in belowground biomass (BGB), aboveground biomass (AGB) and volume. By applying the developed models to the NAFORMA stump data, the estimated mean annual volume, AGB and BGB removals in the entire miombo were 1.71±0.54 m3ha- 1year-1, 1.23±0.37tha-1year-1, and 0.43±0.12 tha-1 year -1 respectively. The drivers of removals were, timber extraction, fire, shifting cultivation, charcoal, natural death, firewood collection, poles, grazing wild, carving, grazing domestic and mining activities. The estimated removed AGC ranged from 0.0 to 1.273tCha-1year-1 with the highest removals accounted by timber and the lowest by mining activities. Since the estimated annual volume removals exceed estimated mean annual increment of 1.6±0.2m3 ha-1yr -1 in miombo woodlands, the removals indicate unsustainability utilization of woodlands resource. This imply that the emission is relatively higher than the sequestration. The results also revealed that removals are more prominent in the following categories; shifting cultivation, production forest, grazing land, general land, village land, Eastern and Southern zones. Furthermore, total annual wood volume, annual volume and carbon per ha lost through extra stump height (ESH) were 3 800 000m-3year-1, 0.098 ± 0.034 m3ha-1year-1 and 0.028±0.009 tCha-1year-1 respectively. Based on these findings, it is recommend that, regional developed models should be applied over a wide range of conditions in miombo woodlands of mainland Tanzania under the threshold of tree diameter sizes used in the modelling. Furthermore, we recommend that the site-specific models should be applied for local inventories in their respective sites. For reducing emissions emanating from removals and by considering national circumstances, all categories of miombo woodlands should be managed although the management (in terms of tree removals) intensity and priorities should consider those categories with unsustainable removals. Similarly, all drivers of removals should be managed and priority should be to those drivers with the highest contribution to removals. Since the estimated annual volume loss through ESH (i.e. 3.8 million m3year-1) is almost ¼ of the annual volume deficit of 19.5 million m3year-1 reported by NAFORMA, the deficit and further removals could be lowered through proper adherence to appropriate harvesting procedures in the miombo woodlands of Tanzania. Moreover, the use of alternative sources of energy particularly clean energy and planting trees for wood energy must continue to be emphasized. Additionally, it is recommend that stumps data should be used to estimate volume and carbon removed and assess drivers of volume and carbon removals in other vegetation types i.e. mangrove forest, lowland forest, humid montane forest and thickets. This would bring tree removal information at national scale and improve future estimates of Forest Reference Emission Level (FREL).