The Importance of Soil Seed Bank Dynamics as Potential Indicators of Desertification Tipping Point

Soil seed banks play a major role in the vegetation dynamics of drylands, where annual rainfall is unpredictable and plants depend on a persistent stage (seeds) to survive over the dry season. The purpose of the study is to understand the behaviour of the rangeland system in terms of soil seed bank dynamics before, during and after crossing the “so called” DTP and to determine whether different management systems plays a role in accelerating the desertification process. Through the use of the Space for Time Substitution Approach the study analysed spatial grazing gradients (gradients radiating from water points) to predict how soil seed banks would respond to long term grazing scenarios. Soil seed bank samples were collected along grazing gradients under two management systems (commercial and communal), processed through seedling emergence method and analysed with SPSS statistical package. Though our results indicated larger soil seed bank under the commercial management system, the seed bank size did not differ significantly along both commercial and communal grazing gradients. Commercially managed sites had a larger seed bank of perennial grasses compared to communal sites. Some of which increased gradually with increasing grazing intensity (Eragrostis trichophora), while other decreased with the increase in grazing intensity (Eragrostis rigidior and Eragrostis pallens). Further testing of other seed processes is still ongoing and will be completed in the 1st quota of 2022. Based on the first results soil seed bank size might not be a good indicator of DTP but rather seed bank life form composition as well as species composition of perennial grasses might serve as good indicators of DTP

An Integrated Framework to Study Ecological Tipping Points in Social-Ecological Systems

Sudden regime shifts or tipping points pose a major threat to various ecosystems and people\u27s livelihoods worldwide. However, tipping points are still hard to predict and often occur without warning. To avoid dramatic social-ecological consequences, it is crucial to understand tipping point behaviour and to identify early warning indicators. Previous studies have hardly implemented an integrated social-ecological approach, which has led to a fragmented understanding and oversimplification of tipping point phenomena. Against this background, we present a systemic research framework that harmonizes ecological and social perspectives to gain a mechanistic understanding of tipping point behaviour. We utilize a social-ecological systems (SES) approach to identify drivers, consequences, and feasible preventive strategies. Our proposed framework consists of a retrospective, a comparative and a prospective perspective; each of them utilizes interdisciplinary studies in both sub systems at multiple scales. The research framework was developed by the members of NamTip, an inter- and transdisciplinary research project aiming to understand and manage desertification tipping points in Namibia’s semi-arid rangelands. The NamTip project represents a practical implementation of the research framework, that uses an integrated, social-ecological study design combining the threefold approach with dynamic modelling. This includes analyses of time-series and archival data, experimental and observational studies, as well as scenario development and exploration of decision-making with local farmers. After the initial practical implementation and with our ongoing evaluation, we are convinced that such an ambitious and complex framework will guide the way to a profound understanding of tipping point phenomena and feasible management options

Proximate and starch composition of marama (Tylosema esculentum) storage roots during an annual growth period

The aim of this study was to determine the most suitable time for harvesting marama (Tylosema esculentum) root as an alternative source of novel starch by evaluating the quality of marama root and its starch during growth periods of 12 months. The effects of time on the proximate analysis of marama roots as well as the thermal properties, size and physicochemical properties of the starch were also investigated. Marama was planted in September and total starch of marama roots on both as is and dry bases increased significantly (p<0.05) from 24 g/kg to 115 g/kg and 259 g/kg to 601 g/kg, respectively, from 2 to 12 months after planting. Amylose content significantly (p<0.05) decreased from about 50.7% to 21.4% of the starch for the same time period. The size of marama root starch granules significantly (p<0.05) increased from 8.6 μm to 15.1 μm. The marama root harvested after 2 months had the highest crude protein content (33.6%). In terms of thermal properties, the peak temperature decreased significantly with time (ranging from 93.0 °C to 73.4 °C), while the ΔH increased significantly with time. The findings indicate that marama should be planted early in summer and harvested between 4 and 8 months for optimal starch before winter. Significance: Proximate and starch characteristics of marama storage roots differ significantly with time of harvest. This suggests that desired functional properties can be achieved by controlling growth time. The marama root harvested at 4 months is highly nutritious, it has high protein content, starch that is high in amylose and is suitable for consumption as a fresh root vegetable in arid to semi-arid regions where few conventional crops are able to survive. Marama root is a climate smart crop and it could potentially contribute to food security in arid regions. The results obtained in this study suggest that the optimum time for harvesting marama as a root vegetable is at 4 months while the optimum time for harvesting marama for its starch is at 8 months. Younger roots have higher amylose, and hence higher gelatinisation temperatures, and therefore may be more suitable to be used as a coating during frying