East-African savanna dynamics: from a knowledge-based model to the possible futures of a social-ecological system

Sub-Saharan savanna ecosystems are undergoing transitions such as bush encroachment, desertification or agricultural expansion. Such shifts and persistence of land cover are increasingly well understood, especially bush encroachment which is of major concern in pastoral systems. Although dominant factors can explain such transformations, they often result from intertwined causes in which human activities play a significant role. Therefore, in this latter case, these issues may require integrated solutions, involving many interacting components. Ecosystem modelling has proved appropriate to support decision-makers in such complex situations. However, ecosystem models often require lots of quantitative information for estimating parameters and the precise functional form of interactions is often unknown. Alternatively, in rangeland management, States-and-Transitions Models (STMs) have been developed to organize knowledge about system transitions and to help decision-makers. However, these conceptual diagrams often lack mathematical analyzing tools, which strongly constrains their complexity. In this paper, we introduce the Ecological Discrete-Event Network (EDEN) modelling approach for representing the qualitative dynamics of an East-African savanna as a set of discrete states and transitions generated from empirical rules. These rules are derived from local knowledge, field observations and scientific literature. In contrast with STMs, EDEN generates automatically every possible states and transitions, thus enabling the prediction of novel ecosystem structures. Our results show that the savanna is potentially resilient to the disturbances considered. Moreover, the model highlights all transitions between vegetation types and socio-economic profiles under various climatic scenarios. The model also suggests that wildlife diversity may increase socio-economic resistance to seasonal drought. Tree-grass coexistence and agropastoralism have the widest ranges of conditions of existence of all vegetation types and socio-economic profiles, respectively. As this is a preliminary use of EDEN for applied purpose, analysis tools should be improved to enable finer investigation of desirable trajectories. By translating local knowledge into ecosystem dynamics, the EDEN approach seems promising to build a new bridge between managers and modellers.

Restoration thinning reduces bush encroachment on freehold farmlands in north-central Namibia

Bush encroachment affects ~45 million ha of Namibia and, without appropriate restoration measures, it negatively affects rangeland productivity and biodiversity. Thinning is a common method to counteract bush encroachment. The thinning strategy applied in north-central Namibia was assessed to examine how effective it has been in reducing bush encroachment. Trees/shrubs were selectively thinned manually, targeting all height classes, except individuals with stem diameters ≥18 cm. We investigated the effects on the vegetation and soil properties using surveys on three freehold farms (in 2016 and 2017) in bush-encroached and previously thinned habitats. Our results revealed significant differences in the mean total nitrogen (TN) content between the treatments; thinned areas had higher TN content which would be beneficial for fast-growing grasses. In the thinned plots, the occurrence probability of red umbrella thorn (Vachellia reficiens Warwa) was significantly reduced, indicating that it was the most harvested species; and umbrella thorn (Vachellia tortilis (Burch.) Brenan spp. heteracantha) was increased, indicating that it favoured reduced densities of dominant species. Natural regeneration was rapid; the tree/shrub abundance in the 0–1-m height class in the thinned area surpassed those in the non-thinned by 34 per cent, ~7.2 years since thinning. Thinning significantly reduced tree/shrub abundances of the 1–3- and >3-m height classes, which was still evident 7.2 years since thinning. Based upon the generalized linear mixed-effects model, tree/shrub counts between treatments may equalize in ~14 and 15 years for the 1–3- and >3-m height classes, respectively. Thinning was effective in reducing tree/shrub abundances and can be used to restore wildlife habitat on the Namibian farmland: however, post-thinning management is required to maintain an open savannah vegetation structure as the 0–1-m height class cohort will eventually grow into mature trees/shrubs.

Impact of Bush Encroachment on Livestock Production and Pastoral Livelihoods in Fentale District, Eastern Ethiopia

The threat of bush encroachment on community livelihoods and economy in range lands of Fentale district in Ethiopia is not well known. So, this study was conducted to evaluate the impact of bush encroachment and its stress on livestock daily milk yield and pastoral livestock production of the district. The data of household livestock holding and its production, household income sources, expenditure, etc. was obtained from district pastoral and agro-pastoral office and the respective pastoral communities. The data was collected through semi-structured questionnaires, focus group discussion and key informant interviews. The data was analyzed through descriptive statistics and regression analysis using Minitab Software. The result revealed that there was an alarming rate increasing of bush encroachment coverage and positive association (P < 0.05) with camel and goat population than cattle and sheep population (P > 0.05) in the study district. Results of current study also revealed that a positive correlation between increasing coverage of bush encroachment and mean daily milk yield of livestock (i.e. cattle, goat and camel) in the study areas. Pastoral producers also perceived the impact of bush encroachment on livestock population trend and milk production in all study sites and applied different adaptation strategies (like feed supplementation and mobility). It is recommended that appropriate intervention options (like bush thinning) of government and other stakeholders is needed to alleviate the current economic bush related challenges of pastoral producers and save the loosing natural resources, even by amendment of pastoral production related policies and its implementation

The socio-economic impacts of bush encroachment in Manthestad, Taung, South Africa

Bush encroachment involves a widespread increase in, and abundance of, woody vegetation in grassland and savanna biomes. This phenomenon has a direct impact on the socio-economic well-being of rural communities and affects livestock owners and those who utilise the land for various other purposes. This study set out to evaluate and gain an understanding of how livestock owners and land users in a typical rural village in South Africa’s North West Province perceive bush encroachment and the impact it has on the community’s ecosystem services. A quantitative, non-experimental, cross-sectional design was used to document the perceptions of the participants regarding bush encroachment and bush control in an attempt to describe characteristics and to find answers to questions related to how local communities are affected by bush encroachment and the control thereof. The results show that encroachment has a significant impact on the socio-economic status of participants. Furthermore, it was found that the vast untapped knowledge of local livestock owners is vital to control bush encroachment, preserve the land for various types of usage and to conserve natural resources. Evaluating participants’ responses and perceptions also contributed significantly to gaining an understanding of how bush encroachment and the control thereof impact rural communities socio-economically. This led the contributors to conclude that raising awareness, actively engaging with the community, imparting skills and offering educational opportunities, creating jobs, merging biophysical activities and promoting active participation are key to the success of programmes aimed at bush control and the resultant improvement of ecosystem services.

Woody vegetation change over more than 30 years in the interior duneveld of the Kalahari Gemsbok National Park

Background and objectives: Long-term studies of woody plants in South Africa are scarce. This study, initiated in the late 1970s, therefore aids understanding of vegetation dynamics in the southern Kalahari by investigating woody vegetation change at and away from a watering point. Methods: At three sites, all woody individuals were counted by species in plots 0.5 or 1 ha in size. Seedlings were noted separately from the >0.2 m group of individuals. Results: Vachellia erioloba and shrub density decreased over time whereas dwarf shrub species’ numbers fluctuated markedly. Additionally, no increase in density of known bush encroaching species (e.g. Grewia flava, Rhigozum trichotomum and Senegalia mellifera) was found in this large conservation area. Discussion and conclusion: The changes in density of the woody species seem to point to the importance of particular rainfall patterns or sequences of events over different years that are responsible for these changes in the southern Kalahari, and the evident lack of bush encroachment in this conservation area supports the notion that bush encroachment in arid savannas is driven primarily by land-use practices and not by elevated carbon dioxide levels that are sometimes provided as cause for encroachment.