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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. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the influence of distance from surface water on riparian woodland communities in the Okavango Delta. Vegetation sampling was conducted in seven sites within the Okavango Delta in 20 m × 10 m belted plots placed perpendicular to the river bank. The plots were placed at 0-10 m, 10-20 m, 20-30 m, 30-40 m and 40-50 m distance classes increasing away from the river bank. Tree height, basal area, species richness, canopy cover and diversity were determined for each distance class. Indicator species analysis was used to determine the characteristic species at each distance class. Single-factor ANOVA and Tukey post hoc analysis were used to compare species diversity, mean tree height, cover and basal area between distance classes. Correlation between distance from surface water and vegetation parameters was sought using Spearman regression analysis. All parameters except for species richness varied significantly ( P < 0.05) along distance from surface water. Distance from surface water was positively correlated all vegetation parameters except for mean species richness/plot. These results show that distance from surface water influences riparian plant community composition and distribution in the Okavango Delta. This implies that riparian plant species can be indicators of long-term hydrologic conditions in the Delta. [ABSTRACT FROM AUTHOR]

Abstract: The annual flood cycle in the Okavango Delta is the basis of subsistence of the local population, providing water, arable land and wetland resources. Additionally, it forms the basis of a large tourism industry. Flooding in the Okavango Delta is, however, very variable both at short and long term time scales. Past research suggested the influence of factors such as tectonic activity, sedimentation, vegetation change or human influence on the spatial distribution of floodwaters. Change in the flooding regime at any given site is thus often perceived as an effect of permanent change in the system, and this perception results in unnecessary demands for engineering interventions in the system. However, it is possible that some of the perceived changes in flood regime are apparent transient effects of non-linearity of the system and variation in hydrological inputs. Hydrometric data and satellite-derived flood maps are analysed here using statistical methods (covariance analysis and double mass analysis) to distinguish between temporal and permanent changes in various parts of the Okavango Delta. The analyses reveal that system non-linearity causes the hydrological responses of the Okavango Delta to be non-proportional to the inputs. Periods of one to several consecutive years are present when flood extents and outflows are either considerably higher or lower (flow or flood regimes) than what would be expected considering the magnitude of inflow. Such effects are visible throughout the entire system, or only in some distributaries, and do not, as previously thought, represent permanent change in flood distribution. However, flood regime change that appears to result from a physical change in the system has been detected. This change has a nature of shift in flood distribution between the Thaoge and the Xudum, with the latter receiving more water after 1997 at the expense of the former and causing 2004 re-flooding of Lake Ngami. [Copyright &y& Elsevier]

We investigated the influence of hydroperiod variation on soil nutrient content in the Okavango Delta seasonal floodplains. Soil samples were collected from eight zones of homogenous vegetation cover after low and high floods and analysed for pH, Na, Mg, Ca, K and P content. A Student's t-test was used to test for differences in pH, Na, Mg, Ca, K and P between soils after low and high floods. The Kruskal-Wallis test was used to compare means of flooding duration and depth between low and high floods. Na, K, Mg, P and pH levels in soils were significantly different (p<0.05) after low floods compared with after high floods. Na content was lower (p<0.05) in Zones 2 and 8 and higher (p<0.05) in Zones 4, 5 and 6 during high flood than during low flood. Ca content was lower (p<0.05) in Zones 1, 2, 3, 4 and 5 and higher in Zone 7 (p<0.05) under high flood than during low flood. Mg content was lower (p<0.05) in Zones 1 and 5 and higher (p<0.05) in Zones 6, 7 and 8 during high flood than during low flood. K content was lower in Zones 1 and 3 and lower in Zones 6, 7 and 8 (p<0.05) during high flood than during low flood. pH was significantly lower and higher after a high flood in Zones 1 and 6, respectively, than during low flood. P content was significantly (p<0.05) higher in all zones after high flood than after low flood. Flooding depth and duration increased (p<0.05) in all vegetation zones during high flood. Our results have direct implications for molapo (flood recession) farming. We recommend that farmers plough immediately after the onset of flood recession when the soil is still moist and rich in nutrients. [ABSTRACT FROM AUTHOR]