Unpredictable rainfall in arid regions results in drier and wetter periods that influence the vegetation dynamics of these systems. Change in such drylands manifests slowly; therefore, long-term vegetation studies are necessary to provide insight into changes over time. The fine-scale mapping of individual plants in permanent plots in arid dwarf shrubland in 1997 and 2024 revealed that individuals of many species in Succulent Karoo shrubland survive for at least three decades. A preceding favourable weather event resulted in shrub recruitment, while a protracted drought resulted in significant mortality. There was no difference between the number of individuals that persisted from 1997 until 2024 (older individuals) and those that recruited after 1997 (younger individuals). Recruitment under nursed conditions occurred more often than in the open. The four consistently common plant species, Aizoon fruticosum, Osteospermum sinuatum, Pteronia pallens and Ruschia spinosa, differed in lifespan, recruitment site and abundance of recruited individuals. Differences in grazing management, ranging from grazing exclusion to moderate grazing, did not influence survival among common succulent and non-succulent shrubs. These arid shrublands appear to include shrub species that show slow continuous recruitment as well as event-driven episodic recruitment, and others that show demographic inertia, lagged responses and event-driven recruitment.
In South Africa, the Albany Thicket ecosystem has been widely promoted for carbon sequestration, yet large uncertainty remains regarding its actual carbon fluxes, particularly under semi-arid and water-limited conditions. Improved, observation-based estimates are, therefore, required to inform restoration investment decisions and the credibility of climate-change mitigation initiatives. In this study, we quantified carbon and water fluxes of a passively restored Portulacaria afra-dominated Great Fish Thicket using eddy covariance measurements over two relatively dry hydrological years (2015-2016 and 2016-2017). Flux observations were compared with outputs from a process-based biogeochemical model (BGC-MAN) and a satellite-derived product (MOD17A2H Version 6). Net ecosystem exchange indicated that the system functioned as a consistent but modest carbon sink, with annual sequestration of 152 g C m-2 yr-1 and 136 g C m-2 yr-1 in the two respective years. Carbon uptake persisted during hot, dry periods, including nocturnal net CO2 assimilation, providing ecosystem-scale evidence of facultative crassulacean acid metabolism (CAM) activity. The BGC-MAN model successfully reproduced daily and seasonal patterns of observed fluxes using independent meteorological data, whereas MOD17A2H substantially underestimated carbon exchange, likely due to the absence of a CAM functional representation. These results demonstrate that P. afra-dominated thicket can act as a carbon sink even under dry conditions, but at rates lower than previously assumed. The findings highlight the importance of incorporating CAM physiology into carbon models and adopting conservative, observation-driven estimates when evaluating the carbon sequestration potential of thicket restoration projects.
Forage quality is one of the most important factors that determines the distribution and grazing patterns of livestock. During senescence, herbaceous plants redistribute nutrients from leaves to roots. This study quantified the decline in nGongoni (Aristida junciformis) grass quality and quantity due to senescence using in situ and Sentinel-2 data. Forage availability status was assessed based on dry matter (DM) content. Chlorophyll content and biomass were used as surrogates for pre-senescent and senescent grass quality and quantity, while average biomass was used to determine the DM. The Random Forest regression yielded coefficients of determination (R2) of 91.3% and 96.6% plus root mean square errors (RMSEs) of 2.12 and 0.55 & micro;g Chl cm-2 for pre-senescent and senescent grass qualities, respectively. The model further yielded R2 values of 70.9% and 94.2%, and RMSEs of 0.34 and 0.02 kg m-2, for pre-senescent and senescent grass quantities, respectively. Optimal predictions of pre-senescent and senescent grass qualities and quantities were achieved using the red-edge and its associated indices, as well as the near-infrared and red band derivatives. The results also showed a decrease in grass quality (17.2 & micro;g Chl cm-2) and quantity (0.89 kg m-2) following senescence. This study helps to understand variability in forage quality and quantity through space and time.
The dispersal of seeds through herbivore ingestion, and their subsequent germination, are vital for tree recruitment in savannas. This study investigated how recovery, retention and germination of seeds of Dichrostachys cinerea and Vachellia tortilis pods fed to goats and sheep differ, and how seed condition (intact vs swollen) affects germination success. Animals were fed pods equivalent to 2.5% of body mass. Seed recovery from D. cinerea was significantly lower than from V. tortilis across both animal species, although retention time was longer for D. cinerea seeds. The proportion of germinated seeds and time-to-germination differed between the pod species, with D. cinerea seeds germinating in higher proportions and quicker than V. tortilis seeds. Gut passage enhanced germination success relative to controls in both animal species (chi(2) = 99.64, p < 0.001), demonstrating a role in breaking dormancy. Seed condition further influenced germination: swollen seeds had 84% lower odds of germinating compared to intact seeds. Gut passage substantially influenced seed fate, while differences between pod species may partly reflect associated nutritional traits, which warrants further investigation.
Bush encroachment is a form of rangeland degradation that reduces the grazing capacity, livestock and wildlife productivity. This study evaluated how sites dominated by encroaching bush species Senegalia mellifera, Dichrostachys cinerea and Terminalia sericea varied in terms of their herbaceous vegetation structure. The herbaceous vegetation data were collected from 42 fixed points per plot, and a total of 27 plots were surveyed. The results showed that Eragrostis trichophora and Stipagrostis uniplumis were the dominant grass species in the three farms, and 48% of the grass species were annuals. The principal component analysis (PCA) showed that S. mellifera sites were associated with Cenchrus ciliaris, Eragrostis lehmanniana and Brachiaria euriciformis. In contrast, D. cinerea sites corresponded with Aristida stipitata, Urochloa brachyura and Enneapogon cenchroides, while herb species and Pogonarthria squarrosa were more closely linked to T. sericea sites. The herbaceous biomass yield of sites dominated by S. mellifera (410 kg DM ha(-1)) was higher compared to the sites dominated by D. cinerea (292 kg DM ha(-1)) and T. sericea (231 kg DM ha(-1)). The study concluded that field sites dominated by different encroacher bush species had varying herbaceous layers, which ecologically implies that woody species exert species-specific effects on understory vegetation.
Vegetation maps are critical tools for the effective management of savanna ecosystems. To inform conservation planning, we mapped, classified and described the diverse vegetation of the Save Valley Conservancy in southeastern Zimbabwe. We utilised a combination of intensive field surveys across 310 sample plots and supervised object-based image analysis of Sentinel-2 satellite imagery. To assess the environmental drivers of vegetation distribution, we analysed 20 topoedaphic and landscape variables using principal component analysis and linear discriminant analysis. We identified 25 distinct vegetation types, recording a total of 315 plant species (247 woody and 68 herbaceous). The landscape was predominantly characterised by woodland communities, with Colophospermum mopane being the most extensive. In accordance with the Plant Available Moisture and Available Nutrients framework, soil physical and chemical properties, specifically clay content, exchangeable base cations and available phosphorus, were identified as the primary bottom-up environmental determinants sorting the plant communities. However, our findings indicate that edaphic constraints alone are insufficient to explain the present vegetation patterns and structural heterogeneity observed across the conservancy. The current, highly variable structural state of these woodlands reflects an active ecological trajectory driven by intense top-down disturbances, specifically the legacy of historical cattle ranching and fire suppression (driving widespread shrub densification) compounded by a rapidly growing elephant population. Establishing the spatial distribution of the conservancy's vegetation and understanding this dynamic interplay between bottom-up soil constraints and top-down disturbance regimes provides a critical scientific foundation for informed management decisions, particularly regarding fire planning, wildlife stocking rates and the targeted mitigation of bush encroachment.
Native woody encroachment is transforming open ecosystems globally, yet its impact on Zimbabwe's high-altitude montane grasslands remains poorly quantified. This study evaluated the ecological impacts of Leucosidea sericea Eckl. & Zeyh. (Rosaceae) encroachment in Nyanga National Park, Zimbabwe. We established 21 plots representing varying levels of encroachment: unencroached, moderately encroached, and heavily encroached. Shrub density increased sharply, exhibiting a threshold effect. Heavily encroached sites supported almost three-times more shrubs and were characterised by near-dominance of L. sericea. Tree height declined markedly along the encroachment gradient, indicating suppression of the tree layer, whereas grass richness and cover remained broadly stable. However, a pronounced functional shift occurred as shade-intolerant, fire-prone Eragrostis acraea was replaced by shade-tolerant Hyparrhenia rufa, implying reduced flammable fuels and dampened fire intensity. These patterns suggest a self-reinforcing transition towards a stable shrub-thicket state that may be resistant to traditional fire management. We recommend early intervention in moderately encroached zones and propose H. rufa dominance as an early-warning indicator of the impacts of native woody encroachment on montane grasslands. Recognising native woody encroachment as a conservation threat on par with invasive alien plants is essential for maintaining the integrity of Zimbabwe's montane grasslands.
Rangeland degradation shapes debates on livestock production and ecosystem sustainability in South Africa's semi-arid Karoo. While numerous restoration techniques have been proposed, evidence of their effectiveness under working farm conditions and over long-time horizons remains limited. This research note synthesises farmer-reported evidence on rangeland restoration practices and outcomes across commercial farms in the Nama-Karoo and Succulent Karoo. Data were collected through structured surveys with 29 experienced farmers and contextualised using published literature on climate, soil and vegetation. Results indicate that restoration success is most strongly associated with adaptive grazing management, particularly conservative stocking and extended rest periods, rather than with specific grazing systems. Passive restoration approaches, including reduced disturbance and natural regeneration, were perceived as robust strategies for stabilising soils and supporting gradual vegetation recovery under variable rainfall. Brush packing as an active restoration was also listed as an effective restoration measure. In contrast, mechanically intensive interventions and reseeding were applied selectively and were widely viewed as costly and unreliable under drought conditions. The findings highlight the resilience of Karoo rangelands when management aligns with ecological constraints and climatic variability. By highlighting farmers' knowledge, the study frames rangeland restoration as risk management and resilience-building rather than rapid rehabilitation.
In Ethiopia, feed shortages driven by land scarcity and climate variability severely limit livestock productivity. Despite decades of watershed-based interventions, comparative evidence regarding their effectiveness remains limited. A cross-sectional survey of 443 households in Sidama and Central Ethiopia compared model and non-model watersheds to evaluate the effectiveness of integrated interventions on improved forage adoption within mixed crop-livestock systems. Data from household interviews, key informants and focus groups were analysed using descriptive statistics, chi-square tests, multiple linear regression and logistic regression. Adoption of improved forages was significantly higher in model watersheds, where farmers allocated more land and had better access to seeds, irrigation and training. Desho (Pennisetum pedicellatum) and elephant grass (Pennisetum purpureum) dominated production, while overall species diversity remained low. Irrigation and training were the strongest predictors of yield, especially during the dry season, while harvesting age consistently influenced productivity. Logistic regression showed that training increased the likelihood of adoption almost tenfold, and model households were almost twice as likely to adopt compared to non-model households. Persistent barriers included seed shortages, land pressure and limited climate knowledge. Integrated institutional and ecological support is essential for initial adoption and for scaling climate-resilient practices across similar socio-economic systems.
Burning and mowing are non-selective defoliations that remove end-of-season growth, reduce uneven grazing, and homogenise forage for the new season. We predicted that annual dormant-season mowing would impact mesic grassland less than burning because of its lower intensity. This hypothesis was tested using winter and spring burning and mowing, combined with different summer mowing regimes, in a long-term experiment in Pietermaritzburg, established in 1950. The interactive effects of summer mowing and dormant-season defoliation on grass abundance, species composition, and diversity were analysed using ANOVA and PERMANOVA. Burning and dormant-season mowing differed significantly in their effects on species composition, but not diversity, while summer mowing exerted an additional influence. Annual dormant-season mowing without summer mows caused the largest shifts in dominant and subdominant grasses, whereas annual burning plus two summer mows had the least effect. Themeda triandra and Heteropogon contortus were favoured by the high-light conditions created by burning and mowing, whereas Aristida junciformis and Tristachya leucothrix thrived under mowing, where litter reduces light. Annual burning largely maintained the original dominant and subdominant grasses, whereas mowing shifted composition, particularly promoting A. junciformis. We conclude that non-selective defoliation can have selective effects on mesic grassland, and mowing cannot substitute for burning.
