Modelling the sedimentation rates using the Wallingford (2004) equations with the aid of NDVI (remote sensing) to assess land degradation was carried out for Malilangwe reservoir catchment in the south eastern lowveld of Zimbabwe. Siltation life of the reservoir was determined from rate of incoming sediment, trap efficiency and reservoir capacity using the Wallingford method. The average rainfall of the study area was about 560 mm while runoff from the catchment ranged from 0.3 mm (minimum) to 199 mm (maximum) with an overall average runoff of 50.03 mm. Results showed that the overall mean annual sediment concentration was approximately 2,400 ppm. The reservoir capacity to inflow ratio was estimated at 0.8 with a sedimentation rate of 120.1 tkm -2 year -1 . Calculated probability of the dam filling is 26.8 %. Results also showed that the siltation life of the reservoir was [100 years according to the Wallingford method. The Normalised Difference Vegetation Index (NDVI) showed progressive decline (p \ 0.05) of the vegetation health from 2000 to 2009. While acknowledging the limitations of techniques used, this study demonstrates in part the effectiveness of sedimentation modelling and remote sensing as a tool for the production of baseline data for assessment and monitoring levels of land degradation in the Malilangwe reservoir catchment.

We tested whether cultivation and fallowing have any significant effect on tree species diversity and dominance in semi-arid Zimbabwe. To this end, we quantified tree species diversity and physiognomy on two soil types (mutapo and bandati) stratified into three land-use categories, i.e., cultivated land, fallow land and woodland. Results showed that tree species diversity was significantly different on the two soil types. Tree species diversity was high on bandati soil and 2 low on mutapo soil. Results also showed that there was significant difference in tree species diversity among the three land-use categories on mutapo soil but no differences on bandati soil.Pairwise comparisons revealed significant differences in species diversity between paired categories on mutapo soil but no significant differences on bandati soil. Tree physiognomy was significantly different among all three land use categories. Colophospermum mopane and Diospyros kirkii were the dominant species within woodlands, while Acacia tortilis subsp.spirocarpa replaced them as the dominant species within the fallow land category. These results indicate that woodland conversion for cultivation purposes has no immediate significant effect on tree species diversity on bandati soil, while it has a pronounced effect on mutapo soil, at least in the short term.

The Lake Habitat Survey (LHS) method has only been applied once in a tropical African reservoir and could potentially be a useful tool for hydromorphological impact assessments. This study (October 2012) tested the application of the LHS method to two Zimbabwean reservoirs, Cleveland and Chivero, which are impacted differently by human activities within their catchments with varying levels of physical impacts and lakeshore use. The Lake Habitat Quality Assessment (LHQA) and Lake Habitat Modification Score (LHMS) were used to assess the habitat quality and the magnitude of human impact on the reservoirs. Cleveland Reservoir LHQA (78 out of 112) and LHMS (16 out of 42) scores are indicative of relatively low human pressure (e.g. angling and canoeing). Results show that although Cleveland Reservoir is coming under increasing anthropogenic pressure, it does not appear to suffer from major alien plant invasion as compared to Lake Chivero, which scored 62/112 and 32/42 for the LHQA and LHMS, respectively. There were no significant differences between the numbers of vegetation layers in the riparian vegetation of the two reservoirs. However, there were significant differences in the number of macrophyte species and shoreline/riparian pressures between the two reservoirs. In conclusion, the use of the LHS can better enhance quality and reliability of lake hydromorphological assessments in tropical systems, where such an investigation is required to support decision making, after adaptations of the method have been made, i.e., inclusion of catchment impacts on lakes and reservoirs in LHS scoring metrics.

We tested the effect of cultivation on butterfly (Nymphalidae: Charaxes) and beetle (Coleoptera: Scarabaeidae: Cetoniinae) species richness and abundance along a cultivation intensification gradient. Results showed significant differences in species richness and abundance between natural woodlands and cultivated landscapes with larger differences in areas of high cultivation intensity. The results indicate that natural woodland clearing for cultivation purposes has negative impacts on arthropod diversity, a situation more severe in highly intensified cultivated areas. Our results imply that mosaics of different land-use units, each in a different phase of clearancecultivation-abandonment-recovery-clearance cycle could counter the negative effects of cultivation intensity on arthropod diversity. RésuméNous avons testé les effets des cultures sur la richesse et l'abondance d'espèces de papillons (Nymphalidae, Charaxes) et de coléoptères (Coleoptera, Scarabaeidae, Cetoniinae) le long d'un gradient de culture toujours plus intensive. Les résultats montrent des différences significatives dans la richesse et de l'abondance des espèces entre les forêts naturelles et les paysages cultivés, les plus grandes différences se situant dans les zones les plus intensivement cultivées. Ils indiquent aussi que la coupe des forêts naturelles pour y pratiquer des cultures a des impacts négatifs sur la diversité des arthropodes, une situation encore lus grave dans les zones où les cultures sont plus intensives. Nos résultats signifient que des mosaïques d'unités territoriales ayant un usage différent, chacune se trouvant à une phase différente du cycle coupe -mise en culture -abandon -rétablissement -coupe, pourraient contrer les effets négatifs de l'intensité des cultures sur la diversité des arthropodes.

This study investigates the dynamics of secondary succession pathways and analyses the prospects of ecosystem recovery on two soil types in the semi-arid mid-Zambezi valley, northern Zimbabwe. Thirtyfive fallow plots of different ages, ranging from one to twelve years since abandonment and twenty 0.09 ha plots of mature woodland were sampled. The results showed observable changes in vegetation features along the chronosequences of recovering fallow plots. There were significant (p B0.05) relationships between fallow age and tree density and tree diameter at breast height (DBH) with an observable decrease in tree diversity with increasing fallow age. The dominant species within the recovering fallow vegetation were different from the defining species within the natural woodlands. Acacia tortilis subsp. spirocarpa exclusively dominated the vegetation in older fallows and it was less clear whether typical woodland species would regain dominance. Therefore, management efforts may have to focus on initiatives aimed at conserving existing woodlands, which will be vital for the maintenance of defining species.