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

Utilizing Perennial Grass Species’ Population Patterns to Detect Looming Desertification Tipping Points in Semi-Arid Regions

Namibia is one of the global dryland regions facing desertification threats due to overgrazing and recurrent drought. This has disastrous effects on forage provision and consequently on local livelihoods. Unfortunately, the mechanisms underlying sudden shifts of rangeland ecosystems towards a desertified state are still poorly understood. The ability to predict desertification tipping points with the aid of suitable ecological indicators is critical to ensure sustainable management of rangeland resources, which are a backbone of rural livelihood in drylands worldwide. Accordingly, we aimed to identify key perennial grass species that can be used as early-warning indicators for desertification tipping points; and to assess their dynamics and response to grazing pressure. The study was conducted in the eastern region (Otjozondjupa) of Namibia where 4 communal areas and 4 freehold farms (commercial) were selected in order to compare perennial grass population responses within differently management land-use systems. A space-for-time approach was used for this purpose, where plots were laid out along local grazing gradients. Data on species occurrence, size structure and recruitment were collected. Preliminary findings show that a sudden decrease or disappearance of some sensitive native perennial grass species along grazing gradients and lack of seedling recruitment could be a useful hint to an approaching desertification tipping point

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