Estimation of tree removals in Miombo woodlands of mainland Tanzania
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Date
2020
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Sokoine University of Agriculture
Abstract
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).
Description
PhD Thesis
Keywords
Miombo woodlands, Tree, Tanzania, Forest management