Browsing by Author "Mganga, Nyatwere"

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    Species allometric models and the effect of wildfires on carbon sequestration and floristic diversity in miombo woodlands of Kigoma region
    (University of Dar es Salaam, 2014) Mganga, Nyatwere
    This study was conducted in order to develop specific allometric models and assess the impact of wildfires on carbon stock and plant species diversity in miombo woodlands of Kigoma Region. Three forests namely Kitwe, a fire suppressed forest, Mgaraganza, a less frequently burnt forest and Ilunde, a frequently burnt miombo were used in this study. Plant species diversity was determined using ShannonWiener diversity index and compared statistically, while similarity of plant species was compared using Czekanowski’s similarity coefficient. Community structure to include stocking rate and basal area was compared among the forests. Vegetation carbon stock was estimated using biomass allometric model so far developed for miombo woodlands and compared using ANOVA. Sequestered carbon in the soil was obtained by using Walkley-Black method. The satellite remotely sensed data of the above-ground carbon was compared with the ground-truthing above-ground carbon data. Linear regressions were used to develop above-ground carbon allometric models for Diplorhynchus condylocarpon and Pseudolachnostylis maprouneifolia. The similarity coefficients were low in all three forests. The most diverse forest was Ilunde, while the least diverse was Mgaraganza forest. Highest stocking rate was recorded in Mgaraganza forest while the lowest was recorded in Ilunde forest. The highest basal area and stock of carbon in vegetation and soils were estimated in Kitwe forest, while the lowest were estimated in Ilunde forest. The above-ground carbon stock obtained by ground-truthing exceeded the remotely sensed carbon in all forests studied. The best fit allometric model in D. condylocarpon was obtained when DBH was used only as the predictor variable. For P. maprouneifolia, both DBH and H were used as predictor variables. It can be concluded that rampant wildfires altered species composition and structure, thereby increasing the diversity of plant species. Since the negative effect of wildfires is species-specific and involves litter reduction, the overall effect is the reduction of vegetation and the soil carbon. High plant species diversity and composition under enhanced vegetation and soil carbon sequestration when early dry season fire is applied requires further studies. For accurate estimations of carbon stock at regional and global scale, many species-specific allometric models should be developed.
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    A study on the impact of heavy metals on the diversity and adaptability of plants around north mara gold mine, Tanzania
    (Unversity of Dar es Salaam, 2010) Mganga, Nyatwere
    Naturally, plants respond differently to elevated levels of heavy metals. Both the impact of gold mining wastes on the diversity of plant species at the study area and their responses to elevated levels of heavy metals had not been documented prior to the work reported in this thesis. Three parallel line transects of 3500m long, 100m apart were established perpendicular to the gold mine wastes. Cover abundance and composition of plant species were systematically recorded using nested quadrats along each transect. At each site where vegetations had been collected, soil samples were collected from depths of 0-15cm and 15-30cm. Samples from each depth were mixed to form a composite sample. Samples of plants and soils were analyzed for heavy metal (Cu, Pb, Cr, Zn, Cd and Ni) levels using AAS. Soils were also analyzed for pH. To assess plant species response to heavy metals, shoot and root portions of 30 plant species randomly sampled from 24 plots were used. Results indicated that there was a decrease of plant diversity and composition with distance from the mine wastes source. However, t-test showed that the decrease was not significant (p > 0.05). In addition, Monte Carlo Permutation test showed that the measured heavy metals were not significantly influencing the distribution patterns of plants. The decrease was probably caused by bioavailable Pb, Cr, Cd and Ni which were above the recommended ranges but not Cu and Zn. Of the species sampled for adaptability analysis; 20, 13 and 9 were found to be heavy metal hyperaccumulators, excluders and indicators/sensitive respectively. A plant species can be an accumulator of one element and/or excluder of or sensitive to another. Although the diversity and composition loss observed is not statistically significant this does not rule out the urgency of conservation measures to protect the flora and fauna of the studied area.