The effect of forest degradation on forest structure and carbon stock in Kiwengwa pongwe forest reserve, Zanzibar

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Sokoine University of Agriculture


This work reported in this dissertation was conducted in Kiwengwa-Pongwe Forest Reserve (KPFR) in Zanzibar. Specifically, the study assessed the forest structure, carbon stock and forest degradation. Eleven transects were laid out in the North – South direction and plots located along each transect. The distance between transects was 600 meters and plots were laid down systematically at intervals of 300 meters along each transect. Clusters of concentric circular plots of 5, 10 to 15 metres radius were established for measurement of diameter at breast height (dbh). The measured trees were grouped into the following classes: <4, 5-10, 11-20 and >20 cm. The forest had composition of 60 species in 52 families, Stand density of 281 stems ha-1, Basal area of 5.75 m2ha-1 and Volume of 33.97 m3ha-1. Biomass was 22.9 tha-1 with a Carbon stock of 11.5 tCha-1. These results were slightly lower than earlier reported (1997) for the same forest, where volume and biomass then stood at 35.37 m3ha-1 and 26.39 tha-1, respectively. The mean Shannon & Wienner species diversity Index ranged from 0.83 at the forest edge to 1.74 at the forest centre, with a mean of 1.34, which is considered to be low to medium. Assessment of forest degradation showed removals of 159 stems ha-1 corresponding to a basal area of 2.6 m2ha-1, volume of 18 m3ha-1, carbon of 6.1tCha-1 and CO2 emission of 12tCO2-e. These results indicated that KPFR is subject to degradation and hence a high potential for enhance carbon sequestration and storage through sustainable forest management. The study recommends that there is a need to upgrade the status of the surveyed forest reserve to improve its forest structure and carbon sequestration and storage potential.



Forest degradation, Forest structure, Carbon stock, Forest reserve, Kiwengwa pongwe, Zanzibar