Keotshephile Kashe

Disaggregating Hydroperiod: Components of the Seasonal Flood Pulse as Drivers of Plant Species Distribution in Floodplains of a Tropical Wetland

Wetland hydroperiod consists of different components, including frequency, duration and depth. A significant proportion of the seasonally flood-pulsed Okavango Delta is inundated for part of each year. Variation in hydroperiod, driven by the interaction of climate and ecological factors, results in a mosaic of vegetation communities. These communities are highly dynamic over temporal and spatial scales. This study aimed to identify quantitative relationships between hydroperiod components and floodplain vegetation, to better understand the potential effects of hydrological change. A stratified random sample of 30 floodplains was surveyed for species composition and abundance. Hydroperiod components for sample quadrats were estimated from remote sensing and field measurement. Ordination demonstrated strong correlations between species composition and flood frequency, duration, years-since-last-flood and depth. Eight statistically discrete vegetation communities were derived from cluster analysis. Generalized linear models of species distributions along hydrological gradients were used to derive frequency and duration optima. Means of these parameters differed significantly between communities. Increasing hydroperiod corresponded with a progression from grasslands through sedge-dominated to aquatic communities. Species in infrequently flooded areas indicated disturbance and a succession trend towards open woodland. In the sedgelands, average depth was the strongest correlate, while in grasslands and aquatic communities, this was duration.

Assessment of benefits and risks of growing Jatropha (Jatropha curcas) as a biofuel crop in sub-Saharan Africa: a contribution to agronomic and socio-economic policies

In sub-Saharan Africa (SSA), the main goals behind the development of a biofuel industry are employment creation and income generation. Jatropha (Jatropha curcas L.) has emerged as a candidate for biodiesel production. It is a non-edible oil producing, drought-resistant plant that can be grown on marginal land with limited water and low soil fertility. However, these are also attributes that typify weedy and invasive plant species. Adding to these concerns are the general questioning of whether biofuel production will reduce Greenhouse gas (GHG) emissions globally. Currently, there is limited information on the potential invasiveness of many biofuel crops, and in particular, the potential risks of cultivating Jatropha. This paper aims to assess the benefits and risks, especially risks, of growing Jatropha for biodiesel production. Jatropha should be screened through a science-based risk-assessment procedure to predict the risk of becoming invasive before it is released for large-scale commercial cultivation. The net GHG savings can be achieved through the cultivation of Jatropha, considering two main factors: no land-use change and crop management without chemical fertilization.

The Influence of Flooding Frequency on Riparian Woodland Plant Community Composition and Distribution in the Okavango Delta, Botswana

This study aimed to determine the influence of flooding frequency on the species composition and distribution of riparian woodland vegetation in the Okavango Delta. Sampling was done in 20m × 50m plots in the Panhandle, Seronga, Jao, Moremi and Boro. Plant cover, seedling density, species richness and diversity were determined at each site. Plant cover was estimated using the modified Braun-Blanquet cover/abundance scale. Annual flooding frequency was also determined at each site. Plant species fell into two assemblages occurring at each site. There was spatial variation in mean cover, density, species diversity and richness in the Okavango Delta. ANOVA followed by Tukey post hoc analysis showed that in Seronga mean seedling density was significantly higher than in Boro and Moremi. In the Panhandle, seedling density was higher (p<0.05) than in Boro while in Jao it was higher (p<0.05) than in Moremi. Species richness was higher (p<0.05) in Seronga, Jao and Panhandle than in Moremi. Species diversity was higher (p<0.05) in Boro, Jao, Panhandle and Seronga than in Moremi. This study has shown that there is a potential to use riparian vegetation to reconstruct historical hydrological gradients