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Most changes in forest cover affect the amount of carbon held in vegetation and soil,
thereby, either releasing carbon dioxide (a greenhouse gas) to, or removing it from the
atmosphere. A study on effects of forest cover change on carbon stock in miombo
woodlands was carried out in Mbeya region at Mbiwe Forest Reserve. Landsat MSS, TM
and ETM+ image data acquired on June 1984, June 1990 and June 2013 were obtained
and used for forest cover change analysis. Inventory data on systematically laid plots were
used to compute the biomass. The forest cover change from the satellite imagery of 1984,
1990 and 2013 (the dependent variables) and road network, villages and cultivated areas
(the independent variables) were used for determining factors of forest cover change and a
logistic linear model was used. Sample plots were established and biomass per hectare of
each measured plots were used as dependent variables and vegetation indices from the
satellite imageries were used as independent variables to formulate models that were used
to estimate biomass of the whole area of Mbiwe Forest Reserve. Finally, the difference of
biomass between 1984 and 1990 and between 1990 and 2013 were computed to obtain the
gain or loss in biomass. The coefficient of 0.50 was used for conversions of biomass to
carbon stock. The results show that there is a change of forest cover and hence carbon
stock between periods under consideration. During the period 1984-1990, closed
woodland decreased by 2 306.2 ha (−4.7%) and 12 748.2 ha (−26%) for the period 1990-
2013. Similarly, in the period 1984-1990, open woodland increased by 2 420.7 ha (5%)
and decreased by 723.3 ha (-1.5%) between 1990 and 2013. Meanwhile, in the period
1984 – 1990, the bushland increased by 436.5 ha (0.9%) and 12 476 (25%) for the period
1990 – 2013. The results revealed that the year 1984 had the highest average carbon stock
58.5 tC/ha followed by year 1990, with 55.7 tC/ha and 2013 had the lowest carbon stock
of 54.8 tC/ha, varying from 0.5 to 199.9 tC/ha. It was revealed that presences of roads and
village centres in and around forest reserves also presences of cultivated areas in the forest
reserves have high effects on forest cover change. This study recommends that forest
reserves need to be protected as for 19 years (1984 – 2013) a total of 15 779.4 ha out of 49
147.7 ha were changed from closed and open woodland to bushland, cultivated land or
bare soil and at the same period a total of 1 796.80 tC were lost as a results of forest cover
change. On the other hand from 1990 – 2013 closed woodland decreased at a rate of 554.3
ha/year, assuming a linear decline. If this continues unabated, it is likely that in the next 10
years the closed woodland will be completely converted to other covers. Therefore more
effort is needed to protect the forest. |
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