Tier 3: Restoration of tipping points
The main objective of Tier 3 is generating action knowledge such as management options enabling stakeholders to restore ‘tipped’ areas. Our research question is: “What are management options in the vicinity of DTPs?” – The study of ‘restoration’ options has a two-fold motivation: a scientific one aiming at determining the degree of reversibility of DTPs; and an applied one, aiming at improving or at least maintaining the livelihood of people in an era of climate change. As found in our literature review, an understudied aspect in TP research is the efficiency of restoration measures such as reseeding and bush thinning, and the impact of changes in C and N stocks and cycling in African savannas. African grasslands are important carbon sinks thus mitigating climate change (Sandhage-Hofmann et al. 2021). Cascading steps of the desertification process may release C stocks and change C cycles, which may affect the ecosystem disservice of greenhouse gas (GHG) emissions. Therefore, Phase 2 will lead a better understanding of carbon and nutrient dynamics to climate and land-use change and, vice-versa, the efficiency of restoration measures under such modified ecosystem properties. Very few studies focus on socio-economic and socio-political dimensions of rangeland restoration in Southern Africa (cf. Stafford et al. 2017). However, restoration measures cannot be efficiently implemented without understanding local conditions such as the capacities of farmers. In consequence, we combine ecological and social science studies to understand socialecological interactions in the study region causing TPs but develop solutions of how to restore them.
Tier 3 (“Restoration of tipping points”) includes the following WPs:
WP 5: Fencing and reseeding as restoration of the desertification tipping point
This WP adopts the above rationale of demonstrating DTPs by a ‘backward’ approach: removing a key driver (grazing) and monitoring the trajectory of recovery. As the response of degraded rangelands to resting can be rapid for some ecosystem properties (e.g., total C) and slow for others (e.g., plant-related flow of matter), we will analyse both soil & vegetation characteristics during Phase 2. Resting will be complemented by reseeding trials to test if this speeds up recovery.
WP 6: Bush thinning as restoration of the alternative tipping point
In Namibia’s Waterberg region, farmers face the alternative tipping point of woody plant encroachment in addition to desertification (see WP2). This phenomenon is also associated with rangeland degradation, but here, palatable perennial grasses are replaced not by bare ground but by woody plants interspersed with bare soil patches. To counteract woody plant encroachment, thinning practices such as manual, semi-mechanized, mechanical, chemical and biological controls are also applied in our study region (mainly on freehold farms) at different intensities to avoid crossing a tipping point. However, it is still unclear whether these measures are successful in counteracting woody plant encroachment and restoring rangeland health. Also, the social, economic, and political conditions that affect the sustainable implementation of bush thinning measures to avoid crossing the tipping point of woody plant encroachment have not been analysed yet. This WP aims to investigate the success of bush thinning activities on rangeland health (soil, soil seed banks, composition and productivity of the grass layer, etc.). In addition, we will study the social, economic, and political conditions that influence the sustainable implementation of restoration measures to avoid the tipping point of woody plant encroachment, jointly with WP 2. Ecological studies will use a chronosequence approach based on existing bush-thinning trials on one freehold farm and three communities. Sampling design for all ecosystem components will be harmonized.