What are the effects of substrate and grass removal on recruitment of <Emphasis Type="Italic">Acacia mellifera</Emphasis> seedlings in a semi-arid environment?

Acacia mellifera is one of the most important encroaching woody plants in southern African savannas. Previous studies found that this species encroaches far more readily on rocky areas than on sandy substrates, although it grows larger on sandy substrates. Rocky substrates are known to retain more water than sandy substrates, which may be of vital importance during recruitment in semi-arid and arid environments. A number of studies have also indicated that competition with grasses may reduce the recruitment and biomass of tree seedlings. We created an experiment in a semi-arid environment (mean annual rainfall = 388 mm) that tested for the effects of rockiness on A. mellifera recruitment. We also tested the hypothesis that grasses effectively compete with A. mellifera in this environment by simulating the effect of grazing by clipping grasses from half the plots in both the rocky and sandy treatments. Significantly more A. mellifera seedlings established in plots where grasses were clipped than in control plots. A. mellifera seedlings had greater biomass on sandy substrates than on rocky substrates. No significant interaction effects were found between substrate and grass clipping treatment for either seedling number or biomass. We conclude that A. mellifera seedlings are more likely to encroach in habitats with low grass density, although they may achieve greater biomass on sandy soils. Thus, it may be the lower grass density rather than rockiness, which increases the encroachment observed in naturally rocky habitats. These results are also consistent with our observations that adult A. mellifera trees are larger on sandy soils than on rocky soils.     

Grazing and neighborhood interactions limit woody encroachment in wet subtropical savannas

Woody encroachment in savannas is a worldwide concern, and there is growing consensus that anthropogenic activities play a central role in changing tree – grass interactions. We evaluated the influence of livestock grazing and neighborhood interactions on seedling emergence and survival of the native tree Acacia caven in wet savannas of northeastern Argentina. We hypothesized that grazing and grass competition act as biotic barriers limiting tree recruitment, but the relative magnitude of such barriers differs according to grass patch type. In two consecutive years (cohort 1 and 2) we sowed seeds and transplanted seedlings of Acacia in two grass patch types (prostrate/palatable and tussock/unpalatable grasses) in both, grazed and ungrazed plots. Each grass patch type was further manipulated to create three levels of grass competition (unclipped control, above-ground biomass removal and total biomass removal).Cattle grazing diminished seedling emergence of both cohorts and seedling survival of cohort 1. The effect of grass competition changed according to grass patch type. Prostrate grass cover enhanced emergence but lowered early survival, while tussock grass cover and also its total biomass removal facilitated early survival. During the second year, a severe drought drastically reduced Acacia recruitment, and it was strong enough to eliminate any grazing effects although the effect of grass competition on seedling establishment remained significant.Our results suggest that grazing and grass competition additively diminished the risk of woody establishment in this wet savanna. However, the stocking rate should be carefully balanced, thus contributing to the maintenance of a competitive grass cover to limit tree recruitment.     

Trees improve grass quality for herbivores in African savannas

The tree–grass interactions of African savannas are mainly determined by varying rainfall patterns and soil fertility. Large savanna trees are known to modify soil nutrient conditions, but whether this has an impact on the quality of herbaceous vegetation is unclear. However, if this were the case, then the removal of trees might also affect the structure and quality of the grass layer. We studied the impact of large nitrogen- and non-nitrogen fixing trees on the sub-canopy (SC) grass layer in low- and high-rainfall areas of differing soil fertility in eastern and southern Africa. We compared the structure and nutrient levels of SC grasses with those outside the canopy. Grass leaf nitrogen and phosphorus contents beneath tree canopies were elevated at all study sites and were up to 25% higher than those outside the canopy in the site of lowest rainfall and soil fertility. Grass leaf fibre and organic matter (OM) contents were slightly enhanced beneath tree canopies. At the site of highest rainfall and soil fertility, grasses beneath the canopy had significantly lower ratios of stem:leaf biomass and dead:living leaf material. Grass species composition differed significantly, with the highly nutritious Panicum spp. being most abundant underneath tree crowns. In the two drier study sites, soil nitrogen and OM contents were enhanced by 30% beneath trees. N-fixation capacity of trees did not contribute to the improved quality of grass under the canopy. We conclude that trees improve grass quality, especially in dry savannas. In otherwise nutrient-poor savanna grasslands, the greater abundance of high-quality grass species with higher contents of N and P and favourable grass structure beneath trees could attract grazing ungulates. As these benefits may be lost with tree clearance, trees should be protected in low fertility savannas and their benefits for grazing wildlife recognised in conservation strategies.     

Seasonality and facilitation drive tree establishment in a semi-arid floodplain savanna

A popular hypothesis for tree and grass coexistence in savannas is that tree seedlings are limited by competition from grasses. However, competition may be important in favourable climatic conditions when abiotic stress is low, whereas facilitation may be more important under stressful conditions. Seasonal and inter-annual fluctuations in abiotic conditions may alter the outcome of tree–grass interactions in savanna systems and contribute to coexistence. We investigated interactions between coolibah (Eucalyptus coolabah) tree seedlings and perennial C₄ grasses in semi-arid savannas in eastern Australia in contrasting seasonal conditions. In glasshouse and field experiments, we measured survival and growth of tree seedlings with different densities of C₄ grasses across seasons. In warm glasshouse conditions, where water was not limiting, competition from grasses reduced tree seedling growth but did not affect tree survival. In the field, all tree seedlings died in hot dry summer conditions irrespective of grass or shade cover, whereas in winter, facilitation from grasses significantly increased tree seedling survival by ameliorating heat stress and protecting seedlings from herbivory. We demonstrated that interactions between tree seedlings and perennial grasses vary seasonally, and timing of tree germination may determine the importance of facilitation or competition in structuring savanna vegetation because of fluctuations in abiotic stress. Our finding that trees can grow and survive in a dense C₄ grass sward contrasts with the common perception that grass competition limits woody plant recruitment in savannas.     

Tree–grass coexistence in savannas revisited – insights from an examination of assumptions and mechanisms invoked in existing models

Several explanations for the persistence of tree–grass mixtures in savannas have been advanced thus far. In general, these either concentrate on competition‐based mechanisms, where niche separation with respect to limiting resources such as water lead to tree–grass coexistence, or demographic mechanisms, where factors such as fire, herbivory and rainfall variability promote tree–grass persistence through their dissimilar effects on different life‐history stages of trees. Tests of these models have been largely site‐specific, and although different models find support in empirical data from some savanna sites, enough dissenting evidence exists from others to question their validity as general mechanisms of tree–grass coexistence. This lack of consensus on determinants of savanna structure and function arises because different models: (i) focus on different demographic stages of trees, (ii) focus on different limiting factors of tree establishment, and (iii) emphasize different subsets of the potential interactions between trees and grasses. Furthermore, models differ in terms of the most basic assumptions as to whether trees or grasses are the better competitors. We believe an integration of competition‐based and demographic approaches is required if a comprehensive model that explains both coexistence and the relative productivity of the tree and grass components across the diverse savannas of the world is to emerge. As a first step towards this end, we outline a conceptual framework that integrates existing approaches and applies them explicitly to different life‐history stage of trees.     

Root dynamics influence tree–grass coexistence in an Australian savanna

Both resource and disturbance controls have been invoked to explain tree persistence among grasses in savannas. Here we determine the extent to which competition for available resources restricts the rooting depth of both grasses and trees, and how this may influence nutrient cycling under an infrequently burned savanna near Darwin, Australia. We sampled fine roots <2 mm in diameter from 24 soil pits under perennial as well as annual grasses and three levels of canopy cover. The relative proportion of C₃ (trees) and C₄ (grasses) derived carbon in a sample was determined using mass balance calculations. Our results show that regardless of the type of grass both tree and grass roots are concentrated in the top 20 cm of the soil. While trees have greater root production and contribute more fine root biomass grass roots contribute a disproportional amount of nitrogen and carbon to the soil relative to total root biomass. We postulate that grasses maintain soil nutrient pools and provide biomass for regular fires that prevent forest trees from establishing while savanna trees, are important for increasing soil N content, cycling and mineralization rates. We put forward our ideas as a hypothesis of resource‐regulated tree–grass coexistence in tropical savannas.     

Self‐thinning and Tree Competition in Savannas

This paper examines the feasibility of applying self‐thinning concepts to savannas and how competition with herbaceous vegetation may modify self‐thinning patterns among woody plants in these ecosystems. Competition among woody plants has seldom been invoked as a major explanation for the persistence of herbaceous vegetation in mixed tree–grass ecosystems. On the contrary, the primary resource‐based explanations for tree–grass coexistence are based on tree–grass competition (niche‐separation) that assumes that trees are inferior competitors unless deeper rooting depths provide them exclusive access to water. Alternative nonresource‐based hypotheses postulate that trees are the better competitors, but that tree populations are suppressed by mortality related to fire, herbivores, and other disturbances. If self‐thinning of woody plants can be detected in savannas, stronger evidence for resource‐limitation and competitive interactions among woody plants would suggest that the primary models of savannas need to be adjusted. We present data from savanna sites in South Africa to suggest that self‐thinning among woody plants can be detected in low‐disturbance situations, while also showing signs that juvenile trees, more so than adults, are suppressed when growing with herbaceous vegetation in these ecosystems. This finding we suggest is evidence for size‐asymmetric competition in savannas.     

A dominance shift in arid savanna: An herbaceous legume outcompetes local C4 grasses

The characteristic vegetation structure of arid savannas with a dominant layer of perennial grass is maintained by the putative competitive superiority of the C₄ grasses. When this competitive balance is disturbed by weakening the grasses or favoring the recruitment of other species, trees, shrubs, single grass, or forb species can increase and initiate sudden dominance shifts. Such shifts involving woody species, often termed “shrub encroachment”, or the mass spreading of so‐called increaser species have been extensively researched, but studies on similar processes without obvious preceding disturbance are rare. In Namibia, the native herbaceous legume Crotalaria podocarpa has recently encroached parts of the escarpment region, seriously affecting the productivity of local fodder grasses. Here, we studied the interaction between seedlings of the legume and the dominant local fodder grass (Stipagrostis ciliata). We used a pot experiment to test seedling survival and to investigate the growth of Crotalaria in competition with Stipagrostis. Additional field observations were conducted to quantify the interactive effect. We found germination and growth of the legume seedlings to be facilitated by inactive (dead or dormant) grass tussocks and unhindered by active ones. Seedling survival was three times higher in inactive tussocks and Crotalaria grew taller. In the field, high densities of the legume had a clear negative effect on productivity of the grass. The C₄ grass was unable to limit the recruitment and spread of the legume, and Crotalaria did outcompete the putative more competitive grass. Hence, the legume is able to spread and establish itself in large numbers and initiate a dominance shift in savannas, similar to shrub encroachment.     

Competitive response of savanna tree seedlings to C4 grasses is negatively related to photosynthesis rate

Savanna tree species vary in the magnitude of their response to grass competition, but the functional traits that explain this variation remain largely unknown. To address this gap, we grew seedlings of 10 savanna tree species with and without grasses in a controlled greenhouse experiment. We found strong interspecific differences in tree competitive response, which was positively related to photosynthesis rates, suggesting a trade‐off between the ability to grow well under conditions of low and high grass biomass across tree species. We also found no competitive effect of tree seedlings on grass, suggesting strong tree‐grass competitive asymmetry. Our results identify a potentially important trade‐off that enhances our ability to predict how savanna tree communities might respond to variation in grass competition.     

Effects of rain, nitrogen, fire and grazing on tree recruitment and early survival in bush-encroached savanna, South Africa

Moisture, nutrients, fire and herbivory are the principal factors governing tree–grass cover ratios of savannas. We investigated tree (Acacia mellifera) recruitment after fire and under conditions of maximum-recorded rainfall, nitrogen addition and grazing in a completely-crossed field experiment. We employed a similar garden experiment with the exception of the fire treatment. Tree germination in the field was extremely low, probably due to below-average natural rainfall in plots that only received natural rain, and insufficient watering frequency in irrigated plots. Due to low germination in the field experiment, no treatment significantly affected tree recruitment. In the garden experiment, frequent watering, nutrient control (i.e. no nitrogen addition) and grazing enhanced tree recruitment with significant interactions between rain, nitrogen and grazing. We infer that above-average rainfall years with frequent rainfall events are required for mass tree recruitment. Grass defoliation makes space and resources available for tree seedlings. Nitrogen enrichment increases the competitive ability of fast-growing grasses more than that of the N₂-fixing tree component. In contrast to conventional wisdom that grazing alone causes encroachment, we suggest that there are complex interactions between the above-mentioned factors and ‘triggering’ events such as unusually high rainfall.     

Is there a temporal niche separation in the leaf phenology of savanna trees and grasses?

Aim It has been proposed that, in tropical savannas, trees deploy their leaves earlier in the growing season and grasses deploy their leaves later. This hypothesis implies a mechanism that facilitates the coexistence of trees and grasses in savannas. If true, this hypothesis would also allow algorithms to use differences in the phenological timing of grass and tree leaves to partition the relative contribution of grasses and trees to net primary production. In this study we examine whether a temporal niche separation between grasses and trees exists in savanna. Location A semi‐arid, subtropical savanna, Kruger National Park, South Africa. Methods We use a multi‐spectral camera to track through an entire growing season the normalized difference vegetation index (NDVI) of individual canopies of grasses and trees at eight sites arranged along a precipitation and temperature gradient. Results Among trees, we identified two distinct phenological syndromes: an early flushing syndrome and a late‐flushing syndrome. Leaf flush in the tree strategies appears to pre‐empt rainfall, whereas grass leaf flush follows the rain. The growing season of trees is 20 (late‐flushing trees) to 27 (early flushing trees) days longer than that of the grasses. Main conclusions We show that grasses and trees have different leaf deployment strategies. Trees deployed leaves at lower temperatures than grasses and retained them for longer at the end of the growing season. The timing of the increase in NDVI is, however, similar between grasses and late‐flushing trees and this complicates the separation of grass and tree signals from multi‐spectral satellite imagery.     

The invasive grass,Melinis minutiflora,inhibits tree regeneration in a Neotropical savanna

Abstract Exotic grasses are becoming increasingly abundant in Neotropical savannas, with Melinis minutiflora Beauv. being particularly invasive. To better understand the consequences for the native flora, we performed a field study to test the effect of this species on the establishment, survival and growth of seedlings of seven tree species native to the savannas and forests of the Cerrado region of Brazil. Seeds of the tree species were sown in 40 study plots, of which 20 were sites dominated by M. minutiflora, and 20 were dominated by native grasses. The exotic grass had no discernable effect on initial seedling emergence, as defined by the number of seedlings present at the end of the first growing season. Subsequent seedling survival in plots dominated by M. minutiflora was less than half that of plots dominated by native species. Consequently, at the end of the third growing season, invaded plots had only 44% as many seedlings as plots with native grasses. Above‐ground grass biomass of invaded plots was more than twice that of uninvaded plots, while seedling survival was negatively correlated with grass biomass, suggesting that competition for light may explain the low seedling survival where M. minutiflora is dominant. Soils of invaded plots had higher mean Ca, Mg and Zn, but these variables did not account for the higher grass biomass or the lower seedling survival in invaded plots. The results indicate that this exotic grass is having substantial effects on the dynamics of the tree community, with likely consequences for ecosystem structure and function.     

A patch-dynamics approach to savanna dynamics and woody plant encroachment – Insights from an arid savanna

The coexistence of woody and grassy plants in savannas has often been attributed to a rooting-niche separation (two-layer hypothesis). Water was assumed to be the limiting resource for both growth forms and grasses were assumed to extract water from the upper soil layer and trees and bushes from the lower layers. Woody plant encroachment (i.e. an increase in density of woody plants often unpalatable to domestic livestock) is a serious problem in many savannas and is believed to be the result of overgrazing in ‘two-layer systems’. Recent research has questioned the universality of both the two-layer hypothesis and the hypothesis that overgrazing is the cause of woody plant encroachment.

We present an alternative hypothesis explaining both tree–grass coexistence and woody plant encroachment in arid savannas. We propose that woody plant encroachment is part of a cyclical succession between open savanna and woody dominance and is driven by two factors: rainfall that is highly variable in space and time, and inter-tree competition. In this case, savanna landscapes are composed of many patches (a few hectares in size) in different states of transition between grassy and woody dominance, i.e. we hypothesize that arid savannas are patch-dynamic systems. We summarize patterns of tree distribution observed in an arid savanna in Namibia and show that these patterns are in agreement with the patch-dynamic savanna hypothesis. We discuss the applicability of this hypothesis to fire-dominated savannas, in which rainfall variability is low and fire drives spatial heterogeneity.

We conclude that field studies are more likely to contribute to a general understanding of tree–grass coexistence and woody plant encroachment if they consider both primary (rain and nutrients) and secondary (fire and grazing) determinants of patch properties across different savannas.     

A stoichiometric perspective of the effect of herbivore dung on ecosystem functioning

Ungulate herbivores play a prominent role in maintaining the tree–grass balance in African savannas. Their top‐down role through selective feeding on either trees or grasses is well studied, but their bottom‐up role through deposition of nutrients in dung and urine has been overlooked. Here, we propose a novel concept of savanna ecosystem functioning in which the balance between trees and grasses is maintained through stoichiometric differences in dung of herbivores that feed on them. We describe a framework in which N₂‐fixing trees and grasses, as well as ungulate browsing and grazing herbivores, occupy opposite positions in an interconnected cycle of processes. The framework makes the testable assumption that the differences in dung N:P ratio among browsers and grazers are large enough to influence competitive interactions between N₂‐fixing trees and grasses. Other key elements of our concept are supported with field data from a Kenyan savanna.     

Positive and negative effects of grass,cattle, and wild herbivores on <Emphasis Type="Italic">Acacia</Emphasis> saplings in an East African savanna

Plant–plant interactions can be a complex mixture of positive and negative interactions, with the net outcome depending on abiotic and community contexts. In savanna systems, the effects of large herbivores on tree–grass interactions have rarely been studied experimentally, though these herbivores are major players in these systems. In African savannas, trees often become more abundant under heavy cattle grazing but less abundant in wildlife preserves. Woody encroachment where cattle have replaced wild herbivores may be caused by a shift in the competitive balance between trees and grasses. Here we report the results of an experiment designed to quantify the positive, negative, and net effects of grasses, wild herbivores, and cattle on Acacia saplings in a Kenyan savanna. Acacia drepanolobium saplings under four long-term herbivore regimes (wild herbivores, cattle, cattle + wild herbivores, and no large herbivores) were cleared of surrounding grass or left with the surrounding grass intact. After two years, grass-removal saplings exhibited 86% more browse damage than control saplings, suggesting that grass benefited saplings by protecting them from herbivory. However, the negative effect of grass on saplings was far greater; grass-removal trees accrued more than twice the total stem length of control trees. Where wild herbivores were present, saplings were browsed more and produced more new stem growth. Thus, the net effect of wild herbivores was positive, possibly due to the indirect effects of lower competitor tree density in areas accessible to elephants. Additionally, colonization of saplings by symbiotic ants tracked growth patterns, and colonized saplings experienced lower rates of browse damage. These results suggest that savanna tree growth and woody encroachment cannot be predicted by grass cover or herbivore type alone. Rather, tree growth appears to depend on a variety of factors that may be acting together or antagonistically at different stages of the tree’s life cycle.     

Multi‐scale patterns and bush encroachment in an arid savanna with a shallow soil layer

Abstract. Question: Bush encroachment (i.e. an increase in density of woody plants often unpalatable to domestic livestock) is a serious problem in many savannas and threatens the livelihood of many pastoralists. Can we derive a better understanding of the factors causing bush encroachment by investigating the scale dependency of patterns and processes in savannas? Location: An arid savanna in the Khomas Hochland, Namibia. Methods: Patterns of bush, grass, and soil nutrient distribution were surveyed on several scales along a rainfall gradient, with emphasis on intraspecific interactions within the dominant woody species, Acacia reficiens. Results: Savannas can be interpreted as patch‐dynamic systems where landscapes are composed of many patches (a few ha in size) in different states of transition between grassy and woody dominance. Conclusions: In arid savannas, this patchiness is driven both by rainfall that is highly variable in space and time and by inter‐tree competition. Within the paradigm of patch‐dynamic savannas, bush encroachment is part of a cyclical succession between open savanna and woody dominance. The conversion from a patch of open savanna to a bush‐encroached area is initiated by the spatial and temporal overlap of several (localized) rainfall events sufficient for Acacia germination and establishment. With time, growth and self‐thinning will transform the bush‐encroached area into a mature Acacia stand and eventually into open savanna again. Patchiness is sustained due to the local rarity (and patchiness) of rainfall sufficient for germination of woody plants as well as by plant‐soil interactions.     

Nitrogen fertilisation reduces grass-induced N2 fixation of tree seedlings from semi-arid savannas

Aims

Coexistence of trees and grasses in nutrient-poor arid savannas may result in competition for soil N. While grasses may be more effective than woody plants in acquiring N from the soil, some leguminous woody species rely on N₂ fixation. We assessed the role of N₂ fixation in the N-budget of Acacia mellifera seedlings by varying N supply and grass competition.

Methods

The contribution of N₂ fixation to the N-budget of Acacia mellifera seedlings with varying N supply and grass competition was determined by measuring growth, nutrient concentrations, and ¹⁵N values.

Results

Tree seedlings were 4-fold taller and had 20-fold more biomass in the absence of grass. Tree foliar δ¹⁵N was lower with (?0.25?±?0.2‰, n?=?9) than without grasses (5.2?±?0.1‰, n?=?64). The contribution of N₂-fixation to the N budget decreased with increasing N supply. Greater reliance on N₂-fixation by trees in the presence of grasses did not result in greater biomass accumulation or tissue [N] relative to tree seedlings grown without grass competition. Tree seedlings competing with grass had significantly more negative δ¹³C (?29.5?±?0.6‰) than seedlings without grass competition (?28.8‰?±?0.5‰).

Conclusions

Induction of N₂-fixation by grass may have resulted from competition for nutrients. N₂-fixation enables tree seedlings to compensate for limited soil N and survive grass competition at a critical and vulnerable developmental stage of germination and establishment.     

Partitioning of root and shoot competition and the stability of savannas

A classic problem in coexistence theory is how grasses and trees coexist in savannas. A popular deterministic model of savannas, the rooting niche separation model, is based on an assumption that is not empirically supported in many savannas. Alternative models that do not rely on the rooting niche assumption invoke intricate stochastic mechanisms that limit their attractiveness as general models of savannas. In this article we develop an alternative deterministic model of grass-tree interactions and use it to analyze the conditions under which grass-tree coexistence is possible. The novel feature of this model is that it partitions aboveground and belowground competition and simulates the fact that fire and herbivory remove only aboveground biomass. The model predicts that stable coexistence of grasses and trees is possible, even when grasses and trees do not have separate rooting niches. We show that when aboveground competition is intense, grasses can be excluded by trees; under such conditions, fire can prevent grasses from exclusion and induce a stable savanna state. The model provides a general framework for exploring the interactive effects of competition, herbivory, and fire on savanna systems.     

A lepidopteran (<Emphasis Type="Italic">Imbrasia belina</Emphasis>) might influence tree-grass balance of <Emphasis Type="Italic">Colophospermum mopane</Emphasis> savanna

Traditional explanations of tree-grass coexistence in African savannas are based on competition between these growth forms or demographic bottlenecks of trees maintained by fire or mammalian browsers. Perturbation of their “balance” may result in an alternate system state of woody encroachment. Invertebrate herbivory has never been offered as an explanation. We developed a consumer-resource model which illustrated that annual irruptions of a lepidopteran (Imbrasia belina), known as mopane worm, can determine the tree-grass balance of semi-arid Colophospermum mopane savanna in southern Africa. Model performance was sensitive to the abundance, hence mortality, of mopane worms, owing to their complete defoliation of tree leaf biomass resulting in altered competitive relations between trees and grasses. Invertebrate herbivores have been recognized in other systems as agents for effecting a state change of host tree populations; this modeling study offers a first indication of such a role for the well-researched tree-grass relations of African savannas.     

Browsing herbivores improve the state and functioning of savannas: A model assessment of alternative land‐use strategies

Changing climatic conditions and unsustainable land use are major threats to savannas worldwide. Historically, many African savannas were used intensively for livestock grazing, which contributed to widespread patterns of bush encroachment across savanna systems. To reverse bush encroachment, it has been proposed to change the cattle‐dominated land use to one dominated by comparatively specialized browsers and usually native herbivores. However, the consequences for ecosystem properties and processes remain largely unclear. We used the ecohydrological, spatially explicit model EcoHyD to assess the impacts of two contrasting, herbivore land‐use strategies on a Namibian savanna: grazer‐ versus browser‐dominated herbivore communities. We varied the densities of grazers and browsers and determined the resulting composition and diversity of the plant community, total vegetation cover, soil moisture, and water use by plants. Our results showed that plant types that are less palatable to herbivores were best adapted to grazing or browsing animals in all simulated densities. Also, plant types that had a competitive advantage under limited water availability were among the dominant ones irrespective of land‐use scenario. Overall, the results were in line with our expectations: under high grazer densities, we found heavy bush encroachment and the loss of the perennial grass matrix. Importantly, regardless of the density of browsers, grass cover and plant functional diversity were significantly higher in browsing scenarios. Browsing herbivores increased grass cover, and the higher total cover in turn improved water uptake by plants overall. We concluded that, in contrast to grazing‐dominated land‐use strategies, land‐use strategies dominated by browsing herbivores, even at high herbivore densities, sustain diverse vegetation communities with high cover of perennial grasses, resulting in lower erosion risk and bolstering ecosystem services.