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Generation of Ecosystem Hotspots Using Short-Term Cattle Corrals in an African Savanna
Abstract
Worldwide, many rangelands are managed for multiple uses, and it is increasingly important to identify livestock management practices that maximize rangeland productivity, biodiversity, and wildlife conservation. In sub-Saharan Africa, pastoralists and ranchers use temporary thorn-fence corrals (“bomas”) to protect livestock at night. Traditional boma sites (used for months or years, then abandoned) develop into productive ecosystem hotspots (“glades”) that attract diverse wildlife and persist for decades or even centuries. In central Kenya, livestock managers have recently begun using metal-fenced “mobile bomas,” which are moved after only days or weeks. Although the assumption is that mobile boma sites will also develop into glades, whether or not this is true remains unclear. We used a broad-scale manipulative experiment to evaluate the ecosystem-level effects of mobile bomas used for 1 month. We also investigated impacts of initial boma density on glade development. We randomly assigned 12 plots to one of three density treatments: one boma, two bomas 200 m apart, or two bomas 100 m apart. Before the experiment and at 1, 6, 12, 18, and 32 months after boma abandonment, we sampled soil nutrients, foliar nutrients, plant communities, and wildlife use (via dung counts) within abandoned boma sites (experimental glades) and at paired reference sites (200 m away). After 18 months, surface soil nutrient concentrations in experimental glades were similar to those in traditionally formed glades. Experimental glade plant communities became dominated by a palatable, rhizomatous grass species, Cynodon plectostachyus. After 32 months, wildlife use by browsing and mixed feeding ungulates was 9 times higher in experimental glades than at paired reference sites. Boma density had few impacts on within-glade development patterns. These results demonstrate that by concentrating livestock in short-term corrals, managers can create ecosystem hotspots that increase functional heterogeneity, attract wildlife, and provide palatable forage for livestock.
... In African savanna ecosystems availability of nutritive forage is important for both domestic and wild herbivores. Old cattle bomas or corrals (also referred to as glades) are considered important nutrient hotspots in east and southern Africa [1][2][3][4][5]. Large herbivores forage in old bomas and also make use of their openness to seek refugee against predators [6]. ...
... Nitrogen is mostly recycled as urine and phosphorus through dung deposition [11]. Some private ranch owners in east and southern Africa are now corralling (hereafter kraaling) cattle overnight for short periods (for example, seven days) in natural rangelands to create nutrient hotspots (hereafter nutrient enriched hotspots) similar to old bomas [1][2][3][4]. ...
... Veblen and Porensky [5] also reported zebra as not actively seeking out high quality forage in nutrient enriched hotspots, presumably, because their large size and hind-gut fermentation allowed them to consume fibrous diets. In addition, low aboveground grass biomass in nutrient enriched hotspots, presumably, made them less attractive to zebra [4]. ...
In east and southern Africa some private ranch owners are corralling (hereafter kraaling) cattle overnight for short periods (for example, seven days) in natural rangelands to create nutrient enriched hotspots which are attractive to large herbivores. However, the effect of season and time after kraal use (alt. age of nutrient enriched hotspots) on large herbivore use of these sites has not been examined. We collated the number of large herbivore sightings per day from camera traps during wet, early and late dry season in nutrient enriched hotspots of varying ages (1, 2, 3 and 4 years) and surrounding vegetation. In addition, above ground grass biomass and height in nutrient enriched hotspots was compared to that of the surrounding vegetation. Furthermore, we tested if repeated grazing in nutrient enriched hotspots stimulated grass compensatory growth. Large herbivore use of nutrient enriched hotspots was similar during wet, early and late dry season. Time after kraal use had a significant effect on mixed feeders (impala and African savanna elephant) utilization of nutrient enriched hotspots but not grazers (zebra and warthog) and browsers (giraffe and greater kudu). Both impala and African savanna elephants mostly used nutrient enriched hotspots one year after kraal use. Aboveground grass biomass and height were higher in surrounding vegetation than in nutrient enriched hotspots. Repeated clipping (proxy for grazing) resulted in compensatory aboveground grass biomass in nutrient enriched hotspots, which declined with time after kraal use. We concluded that nutrient enriched hotspots created through short duration overnight kraaling were important foraging sites for large herbivores.
... The use of short-duration overnight kraals (corrals or bomas) has received considerable attention in the last decade as a potential tool for restoring degraded natural rangeland vegetation (Huruba et al. 2018), sometimes in the context of Holistic Planned Grazing (Peel and Stalmans 2018). Short-duration overnight kraaling systems have been adapted from the traditional long-term cattle corralling, which was used as a way of protecting livestock against predation and theft, and can result in distinct grass patches dominated by grazing-tolerant grass species and high concentrations of nutrients (Blackmore et al. 1990;Porensky and Veblen 2015). Short-duration kraaling is promoted as stimulating grass recruitment and growth through a variety of mechanisms. ...
... In a Kenyan savanna utilised by high densities of wildlife and cattle, single short duration kraaling events resulted in persistent nutrientenriched patches dominated by palatable, grazing tolerant grasses. These patches were maintained for up to three years after kraal abandonment by high densities of wildlife preferentially grazing there (Porensky and Veblen 2015). In contrast, at a more lightly grazed site, the stimulating effects of short-term kraaling on soil nutrients and grass productivity were transient (Sibanda et al. 2016). ...
... The type and intensity of historical herbivory differs between regions in relation to climate and soil nutrient status (Hempson et al. 2015) where only certain areas have conditions that support large herds and intensive grazing. The interaction between resource availability and evolutionary history of mammalian herbivory have led to differences in the life histories in the dominant grass species and hence how grass communities respond to concentrated grazing, trampling (Cingolani et al. 2005) and fire-herbivory interactions ( date, most studies on short-duration kraaling have been done in environments with an evolutionary history of high wildlife diversity and density, for example, Porensky and Veblen (2015) in Kenya, and Sibanda et al. (2016) and Huruba et al. (2018) in Zimbabwe, or sparse herbivory with transient large herds in the Karoo (McManus et al. 2018). In these environments, the effect of short-term kraaling generally increased soil nutrients, as well as palatability and basal cover of grasses. ...
Short-duration overnight kraaling has been suggested as a tool for restoring degraded rangelands. However, the response of different plant functional types and communities to such intense livestock impact may vary depending on local context. We thus examined the effects of short-duration overnight kraaling on soil and vegetation characteristics in a mesic montane grassland in South Africa using paired kraal and control sites, as part of a low intensity grazing approach. Kraaling increased soil P and S, as well as soil organic matter (except when initial values were over 12%). The effect of kraaling on vegetation was strongly dependent on initial condition. Basal cover of grasses and forbs increased by approximately 50 and 15%, respectively, if sites had very low initial basal cover, but decreased by up to 15% if initial values were over 50% and 10%, respectively. Kraaling always decreased herbaceous biomass, but especially when initial values were over 2 000 kg ha⁻¹. In mesic grasslands, short-duration overnight kraaling is promising as a tool for rehabilitating degraded sites or fertilizing abandoned cropland, but should be avoided where the grass sward is intact. We recommend that the suitability of kraaling be evaluated per vegetation type and local context.
... We studied thresholds and tipping points for plant and wildlife response variables in a sub-Saharan African rangeland, where overnight corralling of livestock can be used to precipitate ecological transitions from areas dominated by bare ground to productive "ecosystem hotspots" (Porensky and Veblen 2015). In many regions of sub-Saharan Africa, traditional thorn-fence cattle corrals (bomas) placed on sites ranging from bare-to grass-to tree-dominated, develop into hotspots of unique vegetation composition, high nutrients, and increased use by wild herbivores (Stelfox 1986, Blackmore et al. 1990, Reid and Ellis 1995, Augustine 2003a, van der Waal et al. 2011, Donihue et al. 2013, Ford et al. 2014, Chikorowondo et al. 2017, Marshall et al. 2018, Otieno et al. 2019. ...
... Fortunately, recent technological developments have enabled manipulative experiments that can pinpoint thresholds associated with glade creation. In central Kenya, livestock managers have developed metal-fenced "mobile" bomas, which are both better at protecting livestock against predation and more portable than their traditional thorn-fence counterparts (Porensky and Veblen 2015). Their portability allows managers to intentionally place mobile bomas in degraded bare areas to fertilize and restore vegetation, or to use mobile bomas to create strategically located wildlife hotspots (e.g., Ng'weno et al. 2019). ...
... In contrast, mobile bomas are typically kept in place for much shorter periods, and some managers move their bomas as often as once or twice per week. In central Kenya, Porensky and Veblen (2015) showed that a mobile boma kept in place for one month was sufficient to create a glade-like feature that attracted wild herbivores and provided palatable forage for livestock. In southern Africa, bomas kept in place for 7 d increased the proportion of palatable grasses but produced only a short-term wildlife response (Huruba et al. 2017(Huruba et al. , 2018. ...
Rangelands are governed by threshold dynamics, and factors such as drought, wildfire, and herbivory can drive change across thresholds and between ecological states. Most work on this topic has focused on shifts in a single response variable, vegetation, and little research has considered how to reconcile responses of more than one variable to determine whether a system has undergone a genuine state change. In sub‐Saharan Africa, mobile overnight livestock corrals (bomas) can be used by managers to precipitate ecological transitions from areas dominated by bare ground to productive ecosystem hotspots (glades) that are attractive to wild herbivores. We asked how long bomas must be occupied by cattle before undergoing a state change, considering both plant and animal response variables, to glade ecosystem hotspots. We tested five durations of boma occupation: 0, 4, 7, 14, and 28 days. Each treatment was replicated five times, and we assessed vegetation as well as herbivore dung (as a proxy of use) at multiple time points over 3 yr following boma abandonment. Vegetation in 7‐, 14‐, and 28‐d boma duration treatments appeared to undergo a complete transition to glade‐like plant communities, whereas the shortest 4‐d treatment had not converted to a glade plant community by year 3. Wildlife responses appeared to lag behind vegetation responses, with transitions to glade‐like herbivore use occurring only in the longest duration (14‐ and 28‐d) treatments. Our results show that different response variables, when considered individually, may provide incomplete or misleading information about state changes. Although shorter‐occupied bomas might be effective for reducing bare ground, they may not attract enough wild herbivores to constitute crossing into an alternative state. Understanding threshold dynamics associated not only with vegetation responses but with a broader suite of response variables is challenging, but will provide a more complete representation of ecosystem function and greater opportunity for more successful ecosystem management.
... Thus, while shrubs appear to be stunted by the trampling disturbance, the higher nitrogen could be a result of (1) increased urine and dung, which improves soil fertility, enhancing nutrient In Out quality in the shrub, and (2) the structural damage due to trampling may initiate resprouting that allows nutrients to mobilise to the new shoots (Anderson et al. 2010). This supports previous research findings showing that kraaling increased plant nutrient content, which increased nutrient hotspots in the ecosystem (Porensky and Veblen 2015;Huruba et al. 2018). While the nitrogen content was consistently higher in kraal sites, nitrogen decreased over time in both kraaled and unkraaled areas, which could be attributed to losses in the soil through volatilisation (Huruba et al. 2018). ...
... Our results indicate that grasses dominate the vegetation for at least 12 months after kraaling. Nutrient-rich landscape patches are important in semi-arid environments (Arnold et al. 2014;Porensky and Veblen 2015) and can be increased by short-term kraaling, resulting in heterogeneous vegetation patches (Porensky and Veblen 2015). We suggest that considering the ecology of extinct migrations may offer useful insights in contemporary rangeland ecology. ...
... Our results indicate that grasses dominate the vegetation for at least 12 months after kraaling. Nutrient-rich landscape patches are important in semi-arid environments (Arnold et al. 2014;Porensky and Veblen 2015) and can be increased by short-term kraaling, resulting in heterogeneous vegetation patches (Porensky and Veblen 2015). We suggest that considering the ecology of extinct migrations may offer useful insights in contemporary rangeland ecology. ...
Plant growth forms likely respond differently to disturbances such as trampling. We investigated the trampling effect of 1 600 sheep encamped at night in temporary enclosures (kraals, corrals or pens), which were relocated weekly. To examine trampling effects and regeneration rates of the various growth forms we compared vegeta- tion composition, canopy cover and foliar nitrogen inside and outside kraals, between one and 12 months after the trampling event. We predicted that inside kraals (1) succulent and non-succulent shrubs would be affected more severely than grasses, (2) perennial plant cover would decrease compared with annual plant cover, (3) foliar nitrogen concentrations would increase, and (4) vegetation recovery would be affected by time and rainfall since last use of the kraal. Grasses and shrubs (succulent and non-succulent) responded differently to kraaling. Density and diversity of succulent and non-succulent shrubs decreased, while annual and perennial grass cover inside and outside kraaling areas did not differ. Foliar nitrogen was greater inside kraals. Both succulent and non-succulent shrub cover increased over time after kraaling irrespective of the rainfall. Our study demonstrates that short-term intensive trampling and dunging creates nutrient-rich, heterogeneous patches that may enhance restoration of degraded production landscapes.
... Traditional pastoralism in eastern Africa involves managing livestock across nutrient-poor arid and semi-arid lands characterized by complex mobility strategies to access water and pasture (Kirkbride and Grahn, 2008;Lane, 2013;Galaty, 2021). It also involves keeping livestock in one place overnight, resulting in the accumulation of animal dung from feeding in different habitats (Shahack-Gross et al., 2008;Porensky and Veblen, 2015;Marshall et al., 2018). Since colonial invasion and administrative imposition, traditional pastoralism has been stigmatized as a nonadaptive, wasteful activity that damages the land (Fratkin, 2001;Anderson, 2002;Lankester and Davis, 2016). ...
... These patches are transformed into grassy glades that continuously attract both pastoralists and wildlife (Muchiru et al., 2008;Boles and Lane, 2016). An established cyclical pattern of enrichment promotes the conservation of plant, livestock and wildlife biodiversity (Porensky and Veblen, 2015). Similar habitat enrichment, via analogous forms of pastoralism that constitute a sort of 'bioengineering' , has been documented in arid regions of the world such as Central Asia (Ventresca Miller et al., 2020) and the Andes (Branch et al., 2023). ...
The triple planetary crisis of climate change, pollution, and biodiversity loss necessitates more holistic, comprehensive, and integrated public policy approaches. Within the United Nations Framework Convention on Climate Change, this crisis highlights significant conflicts over forms of knowledge and conceptualization, affecting how international policies are formed. Indigenous knowledge systems have become increasingly acknowledged for their vital role in addressing the challenges of the Anthropocene. Conferences of the Parties institutions like the International Indigenous Peoples Forum on Climate Change emphasize the critical, although not always recognized, importance of Indigenous territories, which contain eighty percent of the world’s biodiversity. Here, we show that research in paleoecology, archaeology and history demonstrates the long-term significance of traditional knowledge and Indigenous land management practices for contemporary ecosystem dynamics. Drawing from these varied studies and perspectives also reveal the socio-economic inequalities resulting from centuries of European colonialism. We showcase three case studies on; (i) pastoralism in eastern Africa, (ii) natural resource management in southeast Asia and (iii) adaptation to sea level rise in the Caribbean, which touch upon highly diverse human resilience strategies across space and time. Despite efforts at the COP28 to accelerate climate action and incorporate diverse knowledge systems, significant challenges remain. The need for a pluralistic knowledge, rather than a one-size-fits-all approach, blending scientific language with artistic and narrative forms, is proposed as critical for fostering effective communication and developing more effective and equitable solutions for global environmental governance.
... Kraals have long been known as sites of nutrient enrichment (Porensky and Introduction Veblen 2015;Veblen 2012). Livestock spend many hours inside these kraals, and large dung and urine deposits may alter soil properties over time (Porensky and Veblen 2015) with knock-on effects on vegetation structure and biodiversity (Jamsranjav et al. 2018). Once abandoned, these sites can have higher grass diversity and biomass than the surrounding areas (Sibanda et al. 2016), and become important foraging areas for wild herbivores (Huruba et al. 2022). ...
... Thus the true range of effect sizes is -4.13 to 9.61 based on 95% prediction intervals. Based on studentised residuals, studies by Rahman et al. (2019) and Porensky and Veblen (2015) had values (+ 2.93) identifying them as potential outliers, while their relatively Cook's distance values also indicated they were disproportionately influential. The GOSH plot ( Figure 1b) revealed that the latter study contributed to a bimodal distribution (red histogram and dots in kernel density estimate) compared to when it was excluded (blue histogram and dots) in the combinational meta-analysis. ...
Knowledge about how pastoralism and kraaling may contribute to desired global objectives, such as soil fertility, is in danger of being lost. We tested whether short duration kraaling increases soil fertility across various biomes and countries via a meta-analysis (random effects model, n = 12 studies). Kraaling approximately doubled soil concentrations of carbon (C), nitrogen (N), phosphorus (P), potassium (K), and slightly increased pH compared to non-kraaled areas (p ≤ 0.0158, all meta-analyses). Results support the idea of persistent nutrient hotspots post kraal abandonment as a generalizable phenomenon. Anecdotes from a case study, the Herding 4 Health Model, supported findings. However, inconsistency scores (I2 ≥ 90%) indicated that while the average effect size was positive, in some cases the true outcome may in fact be negative. Kraal age did not predict soil fertility in our analysis, possibly due to coarse time intervals. Some studies nevertheless found kraal age to be important, with relatively immobile elements such as P persisting over time while N and K decreased. Using kraals to achieve ‘desirable states’ such as wildlife-livestock coexistence, land restoration, and crop fertilisation will require monitoring, and maintenance of fertility within ecological bounds, ideally with inputs from scientists and pastoralists alike as part of global partnerships.
... Due to the concentration of manure, bomas are important hotspots for the emission of greenhouse gases, particularly of nitrous oxide (N 2 O) (Butterbach-Bahl et al., 2020). Moreover, following abandonment, bomas can become nutrient and biodiversity hotspots in savanna areas (Blackmore et al., 1990;Porensky and Veblen, 2015;Stelfox, 1986;Veblen, 2013), which remain visible in landscapes for hundreds of years (Marshall et al., 2018). Traditionally, a single boma can be used for >10 years, particularly when located close to a homestead; however, when pastoralists migrate with their animals in search of forage, a boma can be abandoned within a few days or weeks. ...
... More effective manure practices, for example by reducing the manure accumulation through shortening the active boma lifetime to a few days before moving it to a new position (Carbonell et al., 2021;Stelfox, 1986), could help to better manage grasslands through fertilization and reduction of N 2 O losses (Harris, 2002). While such a rapid boma rotation may be cumbersome with the traditional wooden or thorn-bush bomas, metal-or canvas-fenced mobile bomas are currently promoted in various projects in Eastern and Southern Africa (Conciatore, 2019;Karen Blixen Camp Trust, 2021) with potential benefits including a) better protection from predation, and b) improved rangeland productivity and palatability at the created nutrient hotspots (Peel and Stalmans, 2018;Porensky and Veblen, 2015). However, improved rangeland and manure management is hampered by the lack of data regarding livestock numbers in and movement across pastoral landscapes in East Africa. ...
The use of night-time livestock enclosures, often referred to as "bomas", "corrals", or "kraals", is a common practice across African rangelands. Bomas protect livestock from predation by wildlife and potential theft. Due to the concentration of animal faeces inside bomas, they not only become nutrient-rich patches that can add to biodiversity, but also hotspots for the emission of nitrous oxide (N 2 O), an important greenhouse gas, especially when animals are kept inside for long periods. To provide an accurate estimate of such emissions for wider landscapes, bomas need to be accounted for. Moreover, initial experiments indicated that more frequent shifts in the boma locations could help to reduce N 2 O emissions. This stresses the need for better understanding where bomas are located, their numbers, as well as when they are actively used. Given the recent advances in satellite technology, resulting in high-frequent spectral measurements at fine spatial resolution, solutions to address these needs are now within reach. This study is a first effort to map and monitor the appearance of bomas with the use of satellite image time series. Our main dataset was a dense times series of 3 m resolution PlanetScope multi-spectral imagery. In addition, a reference dataset of boma and non-boma locations was created using GPS-collar tracking data and 0.5 m resolution Pléiades imagery. The reduction of vegetation cover and increase of organic material following boma installation result in typical spectral changes when contrasted against its surroundings. Based on these spectral changes we devised an empirical approach to infer approximate boma installation dates from PlanetScope's near infrared (NIR) band and used our reference dataset for setting optimal parameter values. A NIR spatial difference index resulted in clear temporal patterns, which were more apparent during the wet season. At landscape scale our approach reveals clear spatio-temporal patterns of boma installation, which could not be revealed from less frequent sub-meter resolution imagery alone. While further improvements are possible, we show that small-sized (150-500 m 2) temporary surface changes, such as those that occur when pastoralists use mobile bomas, can be detected with dense image time series like those offered by the PlanetScope constellation. In future, this could lead to better assessment of a) spatio-temporal livestock distribution, b) the contribution of bomas to N 2 O emissions and soil fertility at landscape scale, and c) the uptake of enclosure rotation practices at large spatial scales.
... Historically, sites were cleared of trees in order to construct bomas and the labour involved resulted in these being used for extended periods (Western and Dunne 1979;Veblen and Porensky 2019). Cattle forage during the day in the surrounding landscape and concentrate nutrients into bomas during the night through dung and urine deposition (Augustine 2003;Porensky and Veblen 2015). After abandonment, the concentrated layer of dung and urine develops over time into nutrient-enriched glades dominated by grazing-tolerant grasses, where woody vegetation may either remain absent for decades to centuries (Young and others 1995;Augustine and others 2003;Veblen 2012) or differ in composition from the surrounding matrix (Scholes and Walker 2004). ...
... After abandonment, the concentrated layer of dung and urine develops over time into nutrient-enriched glades dominated by grazing-tolerant grasses, where woody vegetation may either remain absent for decades to centuries (Young and others 1995;Augustine and others 2003;Veblen 2012) or differ in composition from the surrounding matrix (Scholes and Walker 2004). More recently, bomas have been constructed from movable gates and are moved frequently; however, bomas that have been C. Coetsee and others in place for about a month still result in glades with glade-like nutrient-rich vegetation, that attract herbivores and initiate "ecosystem hotspots" (Porensky and Veblen 2015;Veblen and Porensky 2019). ...
We used a long-term herbivore removal experiment where paired exclosure–open treatments were established at the Mpala Research Centre, Laikipia, Kenya, in 1999 to examine changes in soil nitrogen (N) at nutrient-rich glades and adjacent nutrient-poor bushland sites after almost two decades of herbivore removal. Glades in this landscape are created by large inputs of dung and urine from previous long-term corralling of cattle in an otherwise nutrient-poor matrix of woodland (bushland). We predicted (1) a net gain of soil nutrients at bushland sites (that is, inputs of nutrients > losses) and (2) a net loss of soil nutrients at glade sites (that is, inputs of nutrients < losses) following herbivore exclusion. As expected, soil N increased (by 28% after 17 years) with herbivore removal, but remained largely unchanged in the presence of herbivores at low-nutrient bushland sites. However, contrary to our expectations, soil total N in nutrient-rich glades also increased (+ 18%) when herbivores were removed, but declined when grazed (− 11%). Although the underlying mechanisms are unclear, we suggest that increased N fixation by Acacia spp., combined with increased canopy cover and associated tree leaf litter, resulted in elevated soil N following browser removal in low-nutrient bushland sites, while grazer-induced increases in the rate of N transformations between organic and mineral forms resulted in a more “open” N cycle (as evidenced by higher N mineralization rates and foliar N), with increased potential for N loss in gaseous forms, in grazed nutrient-rich glade sites. Grazers and browsers thus appear to affect the N cycle and create and reinforce heterogeneity in unique ways.
... We estimated elephant use by counting dung piles and then crushing them to avoid double counting in nutrient hotspots and surrounding vegetation (control) sites. Dung counts are considered a reliable method of estimating relative animal use of rangelands (Barnes 2001;Young et al. 2005;Porensky and Veblen 2015). Elephant dung counts were done in nutrient hotspots 6, 12, 24, 36 and 48 months after cattle removal and surrounding vegetation. ...
... Our results showed that twenty-four months after kraaling, soil mineral concentration was higher (Ntwice; P -1.4 times; while both Ca and K -1.6 times) compared to the surrounding landscape. Porensky and Veblen (2015) also reported increases in soil nutrients eighteen months after kraaling. The increase in soil nutrients, presumably, improved A. karroo bark nutrient concentration. ...
Elephants are attracted to nutrient hotspots created through short duration overnight cattle corralling (hereafter kraaling) in natural rangelands at Debshan, a mixed cattle-wildlife private ranch in central Zimbabwe, causing severe tree damage. We determined the effect of age of nutrient hotspot (i.e., time after kraal use) on elephant use and the extent of tree damage. Elephant use and tree damage were assessed in nutrient hotspots of varying ages (6, 12, 24, 36 and 48 months after kraal use) and in surrounding landscape. We also compared Acacia karroo bark nutrient and soil nutrient concentration between nutrient hotspots (24 months after kraal use) and the surrounding landscape. Elephant use of nutrient hotspots was highest at 12 and 24 months after kraaling. The most severely damaged trees were in the 12-, 24- and 36-month-old nutrient hotspots. Acacia karroo bark nutrient concentrations (nitrogen, potassium, calcium, magnesium and iron) were higher in nutrient hotspots than surrounding vegetation, while soil nutrients (nitrogen, phosphorus, calcium and potassium) were higher in nutrient hotspots than surrounding landscape. We concluded that elephants mostly used nutrient hotspots 12 and 24 months after kraaling, while severe tree damage occurred 12, 24 and 36 months after kraal use.
... Inside settlements, herding livestock into enclosures concentrates seeds and excrement-and thus nutrientsfrom grazing the surrounding savanna. Once abandoned, former enclosures become highly productive and long-term grassy glades (Muchiru et al., 2008(Muchiru et al., , 2009Porensky & Veblen, 2015). In contrast, for up to several kilometers from settlements, savanna grass biomass may be depressed by livestock grazing (Groom & Western, 2013;Western et al., 2009). ...
... Sedentarization of pastoralists communities has been shown to alter plant productivity (Groom & Western, 2013;Western et al., 2009), woody cover (Porensky & Veblen, 2015;Veblen, 2013), and fire frequencies Veldhuis et al., 2019). Our study demonstrates that sedentarization of pastoralists alters savanna grassland regrowth. ...
Sedentarization of pastoralist communities is reshaping the structure and functioning of tropical savannas. Of particular concern is how permanent pastoral settlements change grassland vegetation inside “protected” areas. In this study, we investigate the spatial impact of pastoral settlements on grassland regrowth in Nech Sar National Park, Ethiopia. Within the National Park, we established herbivore exclosures across the central grassland plains at varying distances from a high concentration of pastoral settlements. Plant species composition, biomass, and regrowth after clipping were measured every 6 months, inside and outside exclosures in close proximity and further away from pastoral settlements. After 18 months, close proximity to high densities of pastoral settlements negatively influenced grassland regrowth compared to further away from pastoral settlements. Excluding herbivores resulted in lower regrowth compared to grazed swards independent of distance from high densities of pastoral settlements. Cover of the dominant grass species Bothriochloa insculpta was lower when grazed and following clipping, whereas Chrysopogon plumulosus cover was higher closer to settlements. These grasses were dominant across the plain; yet further away from settlements there was a higher number of co-dominant grassland species. These findings suggest that subtle changes in grassland community composition, likely following livestock grazing, contribute to spatial differences in savanna grassland regrowth near to and far from pastoral settlements. Furthermore, specific grassland species may be used as indicators of the wider spatial impact of pastoral settlement sedentarization on savanna regrowth. © 2021 The Authors. Biotropica published by Wiley Periodicals LLC on behalf of Association for Tropical Biology and Conservation.
... This phase also shows a significant increase in species-richness compared to active sheep corrals and even to unaltered grasslands. Ruderal plants on abandoned sheep corrals are known to be particularly productive (Porensky and Veblen 2015;Vinograd and others 2019), an effect that persists long-term in African savannahs and is exploited by herbivores (Marshall and others 2018). Though more than 70% of typical grassland species are absent in the first phase, many ruderal and mesotrophic species co-exist, despite high dissimilarities with unimpacted vegetation. ...
... The long periods of abandonment of sheep corrals since Roman times are further characterized by the arrival of numerous stress-tolerant species typical of Mediterranean dry grasslands (for example, Brachypodim retusum, Brachypodium distachyon, Thymus vulgaris) combined with the persistence of ruderals that are absent from unimpacted grasslands (Rubus ulmifolius, Pardoglossum cheiriifolium, Onopordon illyricum, Hordeum murinum, Crepis bursifolia and Capsella bursa-pastoris). Finally, unaltered grasslands show lower species-richness and an absence of highly productive species, suggesting that pastoral legacies in the Mediterranean lead to hotspots of biodiversity and ecosystem services, similar to African sheep corrals (Porensky and Veblen 2015;Marshall and others 2018). ...
À l’heure où l’on invite souvent à « ré-ensauvager » nos paysages, on peut légitimement s’interroger sur la réussite de tels projets. L’emprise actuelle de l’humain sur la nature, mais aussi celle qu’il y a laissée dans le passé – comme les bergers romains quand ils gardaient leur troupeau sur les bords de la Méditerranée – rendent ce vœu peut-être illusoire.
... This phase also shows a significant increase in species-richness compared to active sheep corrals and even to unaltered grasslands. Ruderal plants on abandoned sheep corrals are known to be particularly productive (Porensky and Veblen 2015;Vinograd and others 2019), an effect that persists long-term in African savannahs and is exploited by herbivores (Marshall and others 2018). Though more than 70% of typical grassland species are absent in the first phase, many ruderal and mesotrophic species co-exist, despite high dissimilarities with unimpacted vegetation. ...
... The long periods of abandonment of sheep corrals since Roman times are further characterized by the arrival of numerous stress-tolerant species typical of Mediterranean dry grasslands (for example, Brachypodim retusum, Brachypodium distachyon, Thymus vulgaris) combined with the persistence of ruderals that are absent from unimpacted grasslands (Rubus ulmifolius, Pardoglossum cheiriifolium, Onopordon illyricum, Hordeum murinum, Crepis bursifolia and Capsella bursa-pastoris). Finally, unaltered grasslands show lower species-richness and an absence of highly productive species, suggesting that pastoral legacies in the Mediterranean lead to hotspots of biodiversity and ecosystem services, similar to African sheep corrals (Porensky and Veblen 2015;Marshall and others 2018). ...
Archeological investigations in one of the most species-rich French Mediterranean dry grasslands (La Crau, Southern France) revealed a dense network of ancient sheep corrals dating from Roman to modern times. By analyzing soil chemistry and vegetation across abandonment dates spanning two millennia, we bring to light a persisting signature of Roman, eighteenth century and modern corrals on present-day ecosystems. Community composition and species-richness reflect time after abandon-ment of sheep stables and are linked to long-term persistence of eutrophication from historical sheep concentrations. Our data highlight changes in vegetation that persist two millennia after human impacts ceased. Small-scale pastoral legacies from Roman times continue to have significant impacts on present-day herbaceous plant communities. Our findings point to a need for greater consideration of persisting eutrophication in dry grasslands and of the conservation value of these long-term legacies.
... Livestock at MRC are tended using modified pastoralist methods, including the corralling of individuals overnight in temporary enclosures ('bomas') constructed from spiny Acacia branches or metal fencing. Abandoned boma sites develop into nutrient-rich, grass-dominated 'glades' (Porensky and Veblen 2015), which have lower tree cover and higher soil nutrients than the surrounding savanna habitat and are hotspots of herbivore activity, owing to both the greater nutritional quality of forage and the lower risk of predation conferred by higher visibility (Young et al. 1995, Augustine 2004, Ford et al. 2014, Riginos 2015. Glades should therefore be areas where subshrubs like S. campylacanthum experience associational susceptibility, as a result of their increased apparency amidst grass neighbors and the greater herbivore activity that these clearings attract. ...
... Glade and non-glade habitats differ not just in tree density and herbivory pressure (Ford et al. 2014), but also in plant community composition, soil macronutrients, livestock dung deposition rates and arthropod abundance (Augustine 2003, Veblen 2012, Donihue et al. 2013, Porensky and Veblen 2015, any or all of which might contribute to intraspecific differences in defense investment across habitats. Thus, to isolate the effects of herbivory on plant defense investment in treeless, grass-dominated areas, we surveyed prickle density on 120 S. campylacanthum in five experimentally cleared plots and five adjacent unmanipulated control plots (n = 12 plants/habitat/site × five sites); tree removal occurred ~3.5 years prior to our survey (Ford et al. 2014). ...
... In contrast, populations of less abundant species (i.e., secondary prey) tend to be suppressed by large carnivores, thus creating strong potential for apparent competition (e.g., Sinclair, 1985;Harrington et al., 1999;Owen-Smith and Mason, 2005;Georgiadis et al., 2007a;Chirima et al., 2012). Ranching occurs alongside wildlife in many African savannas, and landscapes in these humanoccupied systems bear the imprint of livestock production in the form of glades: nutrient hotspots that attract wild ungulates and are derived from abandoned corrals or "bomas" (Augustine and McNaughton, 2006;Porensky and Veblen, 2015). Because livelihoods based purely on livestock production are becoming less reliably profitable, a changing mindset-to balance pastoralism with tourism, and potentially wildlife conservationis gaining traction in many areas (Prins et al., 2000;Odadi et al., 2011;Keesing et al., 2018). ...
... Glades vary in their sizes and shapes; we therefore selected and restricted our analyses to 37 glades derived from bomas that we established in 2009 and 2010 (Figure 4). Nineteen of these bomas were established along the edges of open plains as part of an experiment to understand how glades give rise to various edge effects (Porensky and Veblen, 2015;Porensky and Young, 2016). Subsequently, 18 additional bomas were established in the middle of open plains to further quantify resource selection of zebra and survival of hartebeest. ...
Predator restorations often result in apparent competition, where co-occurring prey populations experience asymmetric predation pressure driven by predator preferences. In many rangeland ecosystems, livestock share the landscape with wildlife, including ungulates and the large carnivores that consume them. We examined whether apparent competition reorganized prey communities following restoration of lions (Panthera leo) to a savanna ecosystem, and whether and how livestock management could alter this indirect interaction between lions and their prey. Three lines of evidence supported the hypothesis that Jackson's hartebeest (Alcelaphus bucelaphus lelwel; an ungulate of conservation concern) are suppressed via lion-mediated apparent competition. First, hartebeest exhibited an Allee effect where they were exposed to lions, but displayed negative density-dependent population growth where they were protected from lions. Second, spatial overlap between plains zebra (Equus burchelli; the primary prey of lions) and hartebeest further exacerbated lion predation on hartebeest. Finally, hartebeest were killed selectively by lions, whereas zebra were killed by lions in proportion to their abundance. We then tested whether glades [nutrient-rich hotspots created by abandoned cattle (Bos indicus) corrals] could be used to manipulate top-down control of hartebeest via their influence on the spatial distribution of zebra. Zebra aggregated at glades, and survival of hartebeest increased with increasing distance from glades, suggesting that corrals may be placed on the landscape away from hartebeest to create spatial refuges from lions. Our findings demonstrate how informed placement of livestock corrals can be used to manipulate the spatial distribution of primary prey (zebra), thereby reducing apparent competition suffered by hartebeest. Our work further provides an example of how integrating apparent competition theory with proactive livestock management can improve conservation efforts in multiple-use landscapes.
... To combat these developments, an integrated landscape-scale approach considering various stakeholders and institutions is required, the description of which is beyond the scope of this study. However, from a nutrient cycling perspective, the aim should be to return as much N and other nutrients from the bomas back to the surrounding grassland, for example by spreading boma manure on the grassland or by using short-rotation bomas (Carbonell et al., 2021;Porensky and Veblen, 2015), or to use boma manure as fertilizer for alternative feed production to supplement the grass-based livestock diet. ...
... Grazing lawns in savanna ecosystems can span several square meters to hectares in extent (Archibald, 2008) and exhibit variable levels of persistence that can span from a few months (Cromsigt & Olff, 2008;Davies et al., 2016) to decades (Novellie & Gaylard, 2013), with lawn persistence dependent on a sufficient abundance of megagrazers, such as white rhinoceros (Ceratotherium simum) and common hippopotamus (Hippopotamus amphibius), on the landscape (Cromsigt & te Beest, 2014;Voysey et al., 2023;Waldram et al., 2008). In locations with low or decreasing megaherbivore abundance, expanding grazing lawns beyond hotspots of nutrient enrichment, such as riparian areas (Kanga et al., 2013), termite mounds (Davies et al., 2016), sodic sites (Grant & Scholes, 2006;Verweij et al., 2006) or abandoned cattle corrals (Porensky & Veblen, 2015), remains a challenge. ...
Fire‐herbivory feedbacks strongly influence the formation of grazing lawns in savanna ecosystems. Preliminary findings suggest that small‐scale (<25 ha) fires can engineer grazing lawns by concentrating herbivores on the post‐burn green flush; however, the persistence of such grazing lawns over the longer term and without repeated fire is unknown.
We used high‐resolution Light Detection and Ranging (LiDAR) to investigate the long‐term effects of fire manipulation on short grass structure (height, cover, volume and spatial continuity) and grazing lawn establishment in Kruger National Park, South Africa. We analysed the effects of fire exclusion and experimental burns applied over a 7‐year period (2013–2019) followed by a 1‐year cessation of burning at varying spatial scales during the early and late dry seasons.
Fires contributed a fourfold increase in short grass cover, regardless of fire season or size. The distribution of grass height differed significantly between fire‐induced grazing lawns and recently unburnt parts of the landscape where controlled fires were excluded over the experimental period. The volume (corresponding to bulk density) of short grass on the landscape responded strongly to fires, with grass volume <20 cm in height increasing with both early and late dry season fires.
Early dry season fires caused larger and more homogeneous short grass patches. Furthermore, early dry season fires were more influential in increasing the cover of the shortest grass height class (1–5 cm).
Synthesis and applications. Our results demonstrate that fire‐induced grazing lawns can persist over the longer term, even when fires are no longer applied, leading to the creation of vertical and horizontal heterogeneity in the grass layer. Small‐scale fires, therefore, represent a feasible management approach to expanding grazing lawn extent, potentially benefiting grazer coexistence and diversity.
... There is a large amount of evidence to prove that nutrient addition, either through dung/urine deposition in livestock corrals (Augustine et al. 2011;Van der Waal et al. 2011;Porensky and Veblen 2015), termite mounds (Gosling et al. 2012), or patches of sodic soils (Grant and Scholes 2006) stimulates nutrient hotspots. It remains unknown whether local fertilisation in a nutrient poor system may trigger a transition from tall grass species to short grass species (Coetsee et al. 2010;Zwerts et al. 2015), however it has been proven that elevated soil nutrient levels attract mammalian herbivores to graze, especially when N is added (Schroder 2021;Thapa et al. 2021). ...
Nutrient poor savannas are often characterized by inedible or rarely palatable grasses, which generally provide poor nutrition for mammalian grazers. So-called grazing lawns, with short, stoloniferous edible grasses, could provide high-quality food for grazers, but these lawn grasses are rare in nutrient poor savannas. We tested whether we could use mineral addition to establish grazing lawns in a nutrient poor African savanna, in order to achieve a switch from tall, nutritionally poor to short, highly nutritional grass species. The key finding is that phosphorus and lime, nitrogen and nitrogen and lime supplementation resulted in shift from tall to short grasses within three years, with a higher overall nutrient concentration in the grass leaf, than without supplementation. When grazed, the cover of lawn grasses was higher compared to the other grasses when not grazed, demonstrating the role of grazers in maintaining and expanding lawn grass patches. We conclude that local fertilisation in nutrient poor savannas is a viable method of increasing mineral levels in the soil and grass leaf. We also concluded that grazing results in an increase in lawn grass cover and a combination of fertilisation and grazing can improve forage quality to ensure higher nutrient availability to herbivores.
... One aspect of our non-invasive approach is that host individuals could not be tracked over space and time; thus, individual-level estimates of exposure could not be estimated, including at other areas of the landscape where animals may aggregate, such as grazing lawns [70]. While recent developments in animal tracking and analytical methods to assess direct and indirect contacts from GPS data provide highresolution information on movement and risk [71], analyses are typically restricted to a relatively small number of collared individuals that represent a small fraction of a population; and thus, interspecific contact rates are challenging to measure on a large scale. ...
Globally rising livestock populations and declining wildlife numbers are likely to dramatically change disease risk for wildlife and livestock, especially at resources where they congregate. However, limited understanding of interspecific transmission dynamics at these hotspots hinders disease prediction or mitigation. In this study, we combined gastrointestinal nematode density and host foraging activity measurements from our prior work in an East African tropical savannah system with three estimates of parasite sharing capacity to investigate how interspecific exposures alter the relative riskiness of an important resource – water – among cattle and five dominant herbivore species. We found that due to their high parasite output, water dependence and parasite sharing capacity, cattle greatly increased potential parasite exposures at water sources for wild ruminants. When untreated for parasites, cattle accounted for over two-thirds of total potential exposures around water for wild ruminants, driving 2–23-fold increases in relative exposure levels at water sources. Simulated changes in wildlife and cattle ratios showed that water sources become increasingly important hotspots of interspecific transmission for wild ruminants when relative abundance of cattle parasites increases. These results emphasize that livestock have significant potential to alter the level and distribution of parasite exposures across the landscape for wild ruminants.
... To combat these developments, an integrated landscape-scale approach considering various stakeholders and institutions is required, the description of which is beyond the scope of this study. However, from a nutrient cycling perspective, the aim should be to return as much N and other nutrients from the bomas back to the surrounding grassland, for example by spreading boma manure on the grassland or by using short-rotation bomas (Carbonell et al., 2021;Porensky and Veblen, 2015), or to use boma manure as fertilizer for alternative feed production to supplement the grass-based livestock diet. ...
... The characteristics of GD imply that yaks preferred to graze in areas with lower GD in the previous period (e.g., one month interval in this study). On the one hand, it is inconsistent with the consensus that the herbivores repeatedly visit palatable patches when they are managed by season-long grazing or free grazing [21,51], while our findings also align with the conclusion of a previous study [52] that augmenting animal densities through herding (opposed to fencing) will lead to a decrease in the selectivity for palatable grass species in the savanna. Similarly, Samuels et al. [53] find that herded sheep exhibit reducing consumption of annual herbs but increasing consumption of non-succulent shrubs than the scattered sheep. ...
Simple Summary
We proposed a pragmatic method for quantifying the grazing density (GD) and herding proximities (HP) based on unmanned aerial vehicles. We further tested its feasibility at three typical household pastures on the Qinghai-Tibetan Plateau, China. The proposed method is ideal for studying animal behavior and determining the correlation between the distribution of pastoral livestock and resource usability.
Abstract
Grazing management is one of the most widely practiced land uses globally. Quantifying the spatiotemporal distribution of livestock is critical for effective management of livestock-grassland grazing ecosystem. However, to date, there are few convincing solutions for livestock dynamic monitor and key parameters quantification under actual grazing situations. In this study, we proposed a pragmatic method for quantifying the grazing density (GD) and herding proximities (HP) based on unmanned aerial vehicles (UAVs). We further tested its feasibility at three typical household pastures on the Qinghai-Tibetan Plateau, China. We found that: (1) yak herds grazing followed a rotational grazing pattern spontaneously within the pastures, (2) Dispersion Index of yak herds varied as an M-shaped curve within one day, and it was the lowest in July and August, and (3) the average distance between the yak herd and the campsites in the cold season was significantly shorter than that in the warm season. In this study, we developed a method to characterize the dynamic GD and HP of yak herds precisely and effectively. This method is ideal for studying animal behavior and determining the correlation between the distribution of pastoral livestock and resource usability, delivering critical information for the development of grassland ecosystem and the implementation of sustainable grassland management.
... Pastoralists have also influenced savanna ecology through their creation and abandonment of livestock bomas (thorn fence corrals that pastoralists traditionally use to protect their livestock at night). The importance of bomas, as a long term sources of nutrient-rich, ecosystem hotspots with distinctive plant communities, are well documented in different pastoral areas of the world including Ethiopia (Coppock, 1994;Muchiru et al., 2008); Veblen and Young, 2010; Porensky and Veblen, 2012; Porensky and Veblen, 2015;Seid et al., 2016). Pastoralists also set aside part of their rangelands as physically or socially fenced grazing reserves Huig, 2013), although this is not common among all pastoral groups in Ethiopia. ...
... While conventional bomas are round enclosures made from thorny, woody vegetation (e.g. Augustine et al., 2011;Mwakatobe et al., 2013), recent ones, made of metal or canvas are more effective (Frank, 2011;Porensky and Veblen, 2015). It is known that preventive measures of traditional grazing practice have potential to reduce livestock predation by wolves (Sillero-Zubiri et al., 2004;EC, 2014). ...
Diese Dissertation, befasst sich mit Wechselwirkungen zwischen Weidevieh und Wildtieren und basiert auf der Hypothese, dass sich stark transformierte europäische Landschaften und weniger gestörte afrikanische Savannen gegenseitig als Referenz dienen können. Aufgrund von Parallelen in der Domestikationsgeschichte, fungieren europäische und afrikanische Hausrinder als theoretischer Rahmen. Die Daten wurden mittels Kamerafallen und Interviews in vier Fallstudien erhoben. Die Untersuchungsgebiete befinden sich in räumlicher Nähe zu Schutzgebieten in Deutschland (Nationalpark Unteres Odertal und Naturpark Westhavelland), Namibia (Etosha Nationalpark) und Tansania (Serengeti Nationalpark). Die Ergebnisse zeigen, dass bestimmte Praktiken des Weidemanagements in Deutschland Potential haben, die Nachhaltigkeit der Weidetierhaltung in Afrika zu erhöhen. In Afrika sind die Reaktionen der Wildtierzönosen auf verschiedene Weidesysteme stärker ausgeprägt als in Europa. Ein gemeinsames Phänomen in allen Fallstudien sind hohe Konflikte mit streng geschützten Wildarten. Die Ergebnisse deuten darauf hin, dass Agrobiodiversität nur erfolgreich geschützt werden kann, wenn Managementstrategien den Anforderungen der Landwirte gerecht werden. Es gibt Gemeinsamkeiten zwischen den Untersuchungsgebieten in Deutschland und privatem Farmland in Namibia. Sorgfältige Anpassungen an die standortspezifischen Bedingungen sind erforderlich wenn ein in Europa entwickeltes Weidesystem in Afrika praktiziert wird. Die Ergebnisse aus Tansania sind ein Indikator für die extreme Veränderung der Landschaft und ausgeprägte Mensch-Wildtier-Konflikte. Besonders dort, wo Rinder hohe kulturelle Bedeutung haben, ist es nötig, die Menschen für Nachhaltigkeit im Weidemanagement zu sensibilisieren. Traditionelle Praktiken des schwindenden Pastoralismus erscheinen vielversprechend um die Nachhaltigkeit der Weidehaltung auf kommunalem Land in Afrika zu erhöhen.
... (3) Changes in movement or mobility of livestock affects GHG emissions indirectly through energy expenditure, which results in changes in feed consumed and thus also GHG emissions . Movement may also impact the distribution and concentration of livestock manure, which previous studies have shown to impact GHG emissions (Augustine et al., 2003;Porensky and Veblen, 2015;Butterbach-Bahl et al., 2020). Shock events are likely to alter movement patterns by increasing the distances required to obtain feed resources, or through market closures and restrictions on livestock movement (Butt, 2010). ...
... (3) Changes in movement or mobility of livestock affects GHG emissions indirectly through energy expenditure, which results in changes in feed consumed and thus also GHG emissions . Movement may also impact the distribution and concentration of livestock manure, which previous studies have shown to impact GHG emissions (Augustine et al., 2003;Porensky and Veblen, 2015;Butterbach-Bahl et al., 2020). Shock events are likely to alter movement patterns by increasing the distances required to obtain feed resources, or through market closures and restrictions on livestock movement (Butt, 2010). ...
CONTEXT
Livestock are the primary source of greenhouse gas (GHG) emissions from agriculture in most African countries, but there is a paucity of baseline data and monitoring of GHG emissions from livestock in Africa, particularly for extreme or shock events. The COVID-19 pandemic represents a novels shock to livestock systems and may result in indirect effects on livestock emissions and other Sustainable Development Goals (SDGs). Due to the pandemic in 2020, extensive pastoralist livestock systems in Northern Kenya were subjected to restrictions on movement, increased costs of transportation, and closure of livestock markets.
OBJECTIVE
The objective of this study was to assess the indirect effects of the COVID-19 pandemic on GHG emissions from livestock systems in Northern Kenya using proxy data and a three-part framework based on changes in 1) herd size, 2) feed availability, and 3) livestock movement.
METHODS
We evaluated changes in GHG emissions from livestock systems in Northern Kenya due to the COVID-19 pandemic based on proxy data from crowd-sourced market data, household panel surveys, and remote sensing data on Normalized Difference Vegetation Index (NDVI). Proxy data were obtained before the pandemic in 2019 and after the pandemic in 2020 to compare between years and evaluate the indirect effects of the pandemic and associated restrictions on livestock GHG emissions using the three-part framework.
RESULTS AND CONCLUSIONS
Overall GHG emissions from livestock in Northern Kenya have decreased due to the pandemic and this was largely driven by reductions in herd size. This reduction in GHG emissions occurred despite an increase in GHG emissions from livestock associated with higher feed availability. Decreased livestock movement due to the pandemic contributed to reductions in GHG emissions from livestock, but such reductions were likely to be small due to limited need for livestock to travel longer distances under the prevailing conditions of high feed availability.
SIGNIFICANCE
This research shows that assessments of changes in GHG emissions from livestock systems due to shock events can be conducted successfully based on proxy data and the three-part framework developed here. We found that shock events, such as the COVID-19 pandemic, may lead to unexpected results with respect to the direction and magnitude of changes in livestock emissions depending on contextual factors and environmental conditions. Thus, we call for more spatially explicit and continued data collection to assess and monitor the consequences of shock events on GHG emissions from livestock and related SDGs in Africa.
... A number of studies have theoretically explored the dynamics of the abundance, longevity, and stability of engineered patches (Cuddington et al., 2009;Gurney & Lawton, 1996;Hastings et al., 2007;Wright et al., 2004). However, these dynamics have rarely been tested experimentally (but see Lagendijk et al., 2016;Porensky & Veblen, 2015). Models predict that the proportion of landscape occupied as engineered patches versus background habitat depends on the population size, density-dependent feedbacks, and behavior of ecosystem engineers (Cuddington et al., 2009;Wright, 2009;Wright et al., 2004). ...
Both termites and large mammalian herbivores (LMH) are savanna ecosystem engineers that have profound impacts on ecosystem structure and function. Both of these savanna engineers modulate many common and shared dietary resources such as woody and herbaceous plant biomass, yet few studies have addressed how they impact one another. In particular, it is unclear how herbivores may influence the abundance of long-lived termite mounds via changes in termite dietary resources such as woody and herbaceous biomass. While it has long been assumed that abundance and areal cover of termite mounds in the landscape remain relatively stable, most data are observational, and few experiments have tested how termite mound patterns may respond to biotic factors such as changes in large herbivore communities. Here, we use a broad tree density gradient and two landscape-scale experimental manipulations—the first a multi-guild large herbivore exclosure experiment (20 years after establishment) and the second a tree removal experiment (8 years after establishment)—to demonstrate that patterns in Odontotermes termite mound abundance and cover are unexpectedly dynamic. Termite mound abundance, but areal cover not significantly, is positively associated with experimentally controlled presence of cattle, but not wild mesoherbivores (15–1,000 kg) or megaherbivores (elephants and giraffes). Herbaceous productivity and tree density, termite dietary resources that are significantly affected by different LMH treatments, are both positive predictors of termite mound abundance. Experimental reductions of tree densities are associated with lower abundances of termite mounds. These results reveal a richly interacting web of relationships among multiple savanna ecosystem engineers and suggest that termite mound abundance and areal cover are intimately tied to herbivore-driven resource availability.
... However, to the best of our knowledge, to date no study has presented a full N balance including livestock-related flows from bomas and piospheres. There are studies looking at cattle congregation areas, but they are limited to the exploration of differences in soil N and vegetation inside cattle bomas and its surroundings in pastoral systems (Reid and Ellis 1995, Young et al. 1995, Augustine 2003, Muchiru et al. 2009, Porensky and Veblen 2015, Valls Fox et al. 2015. Young found that vegetation cover (e.g., Digitaria sp., Portulaca oleracea) was up to 24 times higher in former boma areas than in the surroundings several decades after boma abandonment. ...
Pastoral systems are the dominant livestock production system in arid and semiarid regions of sub‐Saharan Africa (SSA). They are often the only form of agriculture that can be practiced due to unfavorable climate and soil fertility levels that prevent crop cultivation. Pastoralism can have negative impacts on the environment, including land degradation, greenhouse gas emissions and other gases to the atmosphere, soil erosion, water pollution and biodiversity loss. Here, we review the current knowledge on nitrogen (N) cycling, storage, and loss pathways, with an emphasis on identification of N emission hotspots. Our review reports a large uncertainty in the amount of N lost as ammonia from excreta and manure storage, as well as N losses via nitrate and DON leaching. We also found that another major N loss pathway (18%), soil N2 emissions, has not yet been measured. In order to summarize the available information, we use a virtual pastoral farm, with characteristics and management practices obtained from a real farm, Kapiti Research Station in Kenya. For outlining N flows at this virtual farm, we used published data, data from global studies, satellite imagery and geographic information system (GIS) tools. Our results show that N inputs in pastoral systems are dominated by atmospheric N deposition (˜80%), while inputs due to biological nitrogen fixation seems to play a smaller role. A major N loss pathway is nitrogen leaching (nitrate > DON) from pastures (33%). Cattle enclosures (bomas), where animals are kept during night, represent N emissions hotspots, representing 16% of the total N losses from the system. N losses via ammonia volatilization and N2O were four and three orders of magnitude higher from bomas than from the pasture, respectively. Based on our results, we further identify future research requirements and highlight the urgent need for experimental data collection to quantify nitrogen losses from manure in animal congregation areas. Such information is needed to improve our understanding on N cycling in pastoral systems in semiarid regions and to provide practical recommendations for managers that can help with decision‐making on management strategies in pastoral systems in semiarid savannas.
... The amount of anthropogenic sediments left after site abandonment is not insignificant -one study found that dung accumulations in livestock pens can be hundreds of meters in diameter and several meters thick (Shahack-Gross et al., 2003). The presence of decayed and burned concentrations of animal dung promotes the development of healthy soils that support grassy glades with highly nutritious grasses that both livestock and wild ungulates actively prefer (Augustine et al., 2003;Muchiru et al., 2008;Porensky et al., 2013;Porensky and Veblen, 2015;Shahack-Gross et al., 2003;van der Waal et al., 2011). ...
In eastern Africa, ecologists have found that when mobile pastoralists abandon their temporary encampments, the accumulation of burned animal dung, wood, and other organic waste enriches the concentration of nutrients (e.g., calcium, phosphorous, magnesium) essential to soil health, in comparison to other soils without prior human habitation. These nutrient-enriched soils promote glade development and greater biodiversity. Geoarchaeological research on the time depth of this anthropogenic “nutrient hotspot” phenomenon has demonstrated that soils at several archaeological sites in southern Kenya still remain enriched in these soil macro- and micro- nutrients after several thousand years. However, soil scientists and geoarchaeologists do not yet understand how these anthropogenic soils vary over the extensive geographic conditions of eastern Africa. The discovery of a Pastoral Neolithic site (ca. 3000 BP) at Luxmanda on the Mbulu Plateau, Tanzania, provides an opportunity to examine if similar patterns of nutrient enrichment can be detected in a different geological and climatic zone. In this paper, we use geochemical and sedimentary analyses to determine how archaeological soils at Luxmanda differ from adjacent off-site soils and known archaeological soils in Kenya, as well as from computationally derived soil nutrient models for eastern Africa. Our results indicate that soils derived from anthropogenic sediments and ashy dung are 4 to 16-fold more abundant in soil macro nutrients relative to off-site or modeled values. This pattern fits previous studies’ observations that elevated macro- and micro-nutrients in soils are strongly correlated with ancient pastoralist habitation sites. We conclude that anthropogenic soils found at Pastoral Neolithic archaeological sites may be a valuable, but unappreciated, soil resource in eastern Africa.
... The plant-available soil N pool is of similar magnitude to the dung N pool (0.04-1.2 g/ m 2 ) in these savannas and they are positively correlated (Pearson's r = 0.84, p = 0.017; see Table S4 for values). Indeed, addition of dung will increase plant-available nutrient pools in the soil, stimulating plant growth and quality, and changing plant species dominance (Blackmore et al., 1990;McNaughton et al., 1997;Porensky & Veblen, 2015;van der Waal, Kool, et al., 2011). Consequently, we argue that competitive interactions between plants in the field are likely frequently influenced by dung nutrient supply levels as in our experiment, and that plants will respond more strongly to dung fertilization in areas with low soil nutrient availabilities. ...
The balance between trees and grasses is a key aspect of savanna ecosystem functioning, and so far, believed to be regulated by resource availability, fire frequency and consumption by mammalian herbivores. Herbivores, however, also impact plant communities through the deposition of growth‐limiting nutrients in their dung and urine. Little attention has been paid to the fact that savanna herbivores produce dung containing different concentrations of nutrients and it remains unknown what the effect of this variation is on tree–grass interactions.
Here, we investigate if stoichiometric differences in dung from browsers and grazers from an African savanna are large enough to influence competitive interactions between N2‐fixing trees and grasses. We performed a competition experiment with seedlings of three common N2‐fixing tree species and three common C4 grass species from a Kenyan savanna. Plants were grown in mesocosms as monocultures or mixtures with dung from either zebra (grazer) or giraffe (browser).
We show that variation in dung nitrogen (N) to phosphorus (P) ratio between these herbivores was large enough to drive the competitive outcome between tree seedlings and grasses. Under zebra dung with a low N:P ratio (3.5), tree seedlings had an advantage due to increased nodulation and N2 fixation. Under giraffe dung with a high N:P ratio (6.4), grasses suppressed nodulation and tree seedling growth.
Synthesis. We identify another potentially important mechanism by which mammalian herbivores can stimulate ecosystem stability, namely through the N:P ratio of their dung. This illustrates how connected browsing and grazing herbivores are in African savannas, through the forage quality they consume, the N:P stoichiometry of their dung and subsequent effects on plant competition.
... Commercial ranches in Kenya often use makeshift enclosures to corral livestock at night with the objective of targeted dung concentration to generate areas of highly nutritious vegetation. Mixed livestock-wildlife operations may employ this system to create areas of attraction for herbivore wildlife for purposes of touristic game viewing (Porensky and Veblen, 2015). ...
In many parts of the world, the utilization of rangelands is based on the targeted movement of herds within and across often vast territories. Crucial for the success of these livestock operations are decisions on how to flexibly allocate animals to the existing vegetation, both in terms of numbers and concentrations, and in space and time. Research from large scale ranching in the prairies of the Americas, and nomadic or transhumant livestock systems in Africa, the Middle East, and Central Asia, suggests that the more precisely specific patches of vegetation at a specific development stage can be targeted, the more beneficial will be the outcome in terms of animal nutrition and productivity. This also holds for the provision of environmental services such as aboveground net primary production, biodiversity preservation, and soil fertility. However, herding requires year-round labor investment, and in rural areas where seasonal migration is an important livelihood strategy, herding may suffer from absence of skilled workforce. Additional obstacles are political neglect and land use competition, insecurity, reduced self-ownership rates of herds, partial social isolation of herders, and hardship of the work. These make herding an increasingly unpopular occupation, especially for the young generation, but there are also factors that drive (young) people to take up or continue this profession. Reduced herding efforts, reflected in the reluctance to utilize remote grazing areas, may lead to overstocking of favorable pastures. This increases the risk of pasture degradation, long-term reduced herd productivity, social conflict, and public criticism of pastoralism as an anachronistic lifestyle and detrimental land stewardship, thereby further fueling the erosion of herding. By reviewing studies from Africa, the Middle East, and southern and eastern Asia, and including some insights from Europe and southern America, we discuss the ecosystem services produced by herding and herd mobility, and reflect on the ecological and social consequences of the loss of herding labor. Highlighting aspects that speak for this occupation at the individual level, we conclude by suggesting interventions that may sustain the herding profession, such as facilitation of labor sharing, labor contracts, improved herder security, and societal payments for ecological and cultural services.
... A reduction in bare ground is likely a result of increased compensatory growth to defoliation because of increased basal vegetation cover. Other studies have found similar effects when livestock are corralled into small areas, thereby concentrating dung and enhancing vegetation basal cover (Porensky and Veblen 2015) or mitigating woody plant encroachment (Veblen 2013;Venter et al. 2018). Soil moisture, a factor not tested in our pot experiments, is likely also a significant contributor to growth responses in the field plot and farm trial experiments where dung application and soil type both enhanced moisture availability in association with enhanced nutrients. ...
Rangeland management approaches, including rotational grazing, rely on assumptions about plant growth responses to the intensity, or severity (sward height) plus frequency, of defoliation. We tested these assumptions at the farm, patch and plant scale using data from a grazing management trial in an Eastern Cape mesic grassland of South Africa along with field plot and glasshouse pot experiments. The grazing trial tested season-long grazing (SLG), four-camp grazing (FCG) and holistic planned grazing (HPG) at equivalent stocking rates over three years. We found that grass growth responses in both potted plants and field plots were reduced under more frequent and severe defoliation but that this was mitigated under elevated soil nutrients, in line with the Compensatory Continuum Hypothesis which predicts that compensatory growth will increase across an increasing fertility gradient. In the farm trial, SLG, which theoretically causes high frequency, low severity defoliation, reduced bare ground cover and increased vegetation greenness with increasing defoliation intensity on nutrient-rich soils. This effect was not present under FCG or HPG and disappeared under very high defoliation intensities and on relatively water- and nutrient-poor soils. Managers are advised to only increase grazing frequency on relatively high nutrient soils, while maximizing recovery on poorer nutrient soils.
... Marshall et al. (2018) drew on soil chemistry and microstratigraphic analyses to illustrate the construction of so-called "hot spots" on pastoral landscapes in northeast Africa. Many other ecologists and archeologists have noted similar trends on heavily grazed lands Reid, 2012;Riginos et al., 2012;Veblen, 2012;Porensky et al., 2013;Porensky and Veblen, 2015). For example, the construction and maintenance of ecological hot spots by caribou (reindeer) in the tundra and sub-tundra, with notable concentrations of dung near ice patches, date back 5000 years (Andrews et al., 2012). ...
Ecosystem engineering is an innovative concept that recognizes that organisms impact their environment, and that these changes can be detected over time. Thus, additional datasets from the ecological longue durée are necessary, specifically in response to the onset of the Anthropocene and the impacts of humans and their commensal organisms upon ecologies of all scales. For example, the management and herding of domesticated animals are recognized as having dramatic implications for soil stability, vegetation coverage, and even atmospheric composition the world over. Yet, the point at which pastoralism became a recognizable factor in altering earth systems, with large-scale environmental ramifications, is poorly understood. Here, we respond to this by reviewing and presenting data from the archeological and paleoenvironmental record across northern Central Asia in order to assess broader ecosystem impacts of pastoralism, from time periods when this economic pattern was a relatively novel component of local ecologies and involved limited population densities, through to periods in which it became intensive, coincident with agriculture, and linked to increased sedentism. Probing diverse, published analytical datasets and case studies, we examine pastoral adaptations and environmental impacts, highlighting a region where tensions surrounding resilience and sustainability of pastoralism have peaked in modern times. We draw upon these findings to examine the challenges faced by pastoralists today, and the ways in which archeological data might inform on management decisions into the future.
... Similarly, by collecting information on the suitability of different restoration strategies in areas with similar land potential, information on best practices can be obtained and replicated in other locations with matching land potential and degradation characteristics. For example, the use of mobile cattle corrals, or "bomas" as tools to create vegetation hotspots is an increasingly popular restoration tool in many parts of Africa (Porensky andVeblen 2015, Sibanda et al. 2016). However, very little information exists about how effective these bomas are on different soil types, textures, slopes, and climates. ...
... In what Pineiro et al. (2010) called a spatial 'uncoupling' of nutrients, vegetation and its associated organic matter and nutrients can be harvested in one area, but returned via dung and urine to a different part of the pasture altogether. This exodus of nutrients and organic matter from certain areas, and their accumulation in other areas, can have profound effects on patterns of vegetation production and community composition, as well as on nutrient cycling processes at the pasture and/or landscape-scale (Augustine, 2003;Porensky and Veblen, 2015). . ...
Nutrient inputs from cattle dung are crucial drivers of nutrient cycling processes in grazed ecosystems. These inputs are important both spatially and temporally and are affected by variables such as grazing strategy, water location, and the nutritional profile of forage being grazed. Past research has attempted to map dung deposition patterns in order to more accurately estimate nutrient input, but the large spatial extent of a typical pasture and the tedious nature of identifying and mapping individual dung pats has prohibited the development of a time- and cost-effective methodology. The first objective of this research was to develop and validate a new method for the detection and mapping of dung using an unmanned aerial vehicle (UAV) and multispectral imagery. The second objective was to quantify change over time in water-extractable organic carbon (WEOC), water-extractable phosphorus (WEP), and water-extractable nitrogen (WEN) in naturally-deposited dung that ranged from one to twenty-four days old. In addition, pre-analysis dung storage methods (refrigeration vs. freezing) were evaluated for their impact on laboratory analyses results. Multispectral images of pastures were classified using object-based image analysis. Post-classification accuracy assessment showed an overall accuracy of 82.6% and a Kappa coefficient of 0.71. Most classification errors were attributable to the misclassification of dung as vegetation, especially in spectrally heterogeneous areas such as trampled vegetation. Limitations to the implementation of this method for identifying and mapping cattle dung at large scales include the high degree of geospatial accuracy required for successful classification, and the need for additional method validation in diverse grassland environments. Dung WEN concentrations ranged from 1.20 g kg-1 at three days of age, to a low of 0.252 g kg-1 at 24 days. The highest WEOC values were in day-old dung, 19.25 g kg-1, and lowest in 14-day-old dung, 2.86 g kg-1. WEOC and WEN both followed exponential decay patterns of loss as dung aged. WEP was lowest at 1.28 g kg-1 (day one) and highest at 12 days (3.24 g kg-1), and dry matter and WEOC concentration were stronger determinants of WEP than age alone. Freezing consistently increased WEN and WEOC concentrations over fresh values, but WEP was inconsistent across ages in its response. This research provides new insight into dung nutrient dynamics and presents a novel method for studying them across large spatial and temporal scales. Advisors: Martha Mamo and Jerry Volesky
... Management can influence many variables underlying heterogeneity, i.e., protected area design relative to ecological gradients Fynn and Bonyongo 2011), the scale and heterogeneity of clear felling of forests (Rettie and Messier 2000), and the maintenance of large distance gradients from permanent water (Russell et al. 2011;Sianga et al. 2017). Additionally, induced heterogeneity can be created by using patchy fires regimes (Fuhlendorf et al. 2009), strategic grazing by livestock (Shamhart et al. 2012;Fynn et al. 2016;Tyrrell et al. 2017), and the creation of nutrient hotspots in landscapes through corralling of livestock (Muchiru et al. 2008;Augustine et al. 2011;Porensky and Veblen 2015). Creating greater heterogeneity in plant composition and structure across landscapes, not only increases the opportunity for adaptive foraging options for ungulates, but also increases niche diversity for biodiversity (Derner et al. 2009;Fuhlendorf et al. 2009Fuhlendorf et al. , 2017Fynn et al. 2016;Sianga et al. 2017). ...
As anthropogenic influences on the world’s rangelands accelerate, there is an urgency for humanity to develop a greater understanding of key drivers, and processes, underlying ecological dynamics and function, to inform improved management strategies. Browsing and grazing ungulates are important components of human-dominated and natural ecosystems, contributing to agricultural output and associated livelihoods, as well as to biodiversity and ecosystem services. A review of key concepts pertinent to the dynamics and management of browsing and grazing ungulates highlights the emergence of functional heterogeneity as a general, or unifying, theme guiding their management, whatever the scale or system. It is also clear that management of ungulate density, and the intensity of herbivory, especially in smaller-scale sedentary systems (e.g. ranches or small protected areas), is a critical determinant of functional heterogeneity. We demonstrate how the functional heterogeneity concept can be applied to the management of grazing and browsing ungulates over a range of scales and ecosystems.
... Both the magnitude and net positive vs. negative impacts of grazing depend greatly on ecosystem context (see below). In some cases, grazers can be deliberately managed to increase landscape heterogeneity to benefit wildlife (Porensky and Veblen 2015), whereas in other cases grazing is more likely to homogenize the landscape (Adler et al. 2001). It also may be possible to manage grazers to consume and decrease exotic plant (Diamond et al. 2009) or shrub (Dziba et al. 2007) cover and, depending on the properties of the plant community, reduce fire risk by reducing fuel loads (Strand et al. 2014). ...
... Second, we used generalized linear mixed-effect models to estimate species 9 survey-specific RSF coefficients. We tested for selection of three continuous variables known to influence the abundance and distribution of lion prey on the landscape: (1) NDVI (normalized difference vegetation index, a metric associated with visibility, see Resource selection functions for kill sites); (2) distance to glades (nutrient-rich grazing lawns derived from livestock corrals [Augustine et al. 2003, Porensky andVeblen 2015, ]); and (3) distance to water sources (Valeix et al. 2009b). Further, because the abundance and distribution of lion prey can change seasonally (e.g., Ogutu et al. 2008, Kiffner et al. 2014), we evaluated differences in selection between wet (March-May, August-November) and dry (June-July, December-February) season sampling. ...
The vulnerability of an individual to predation depends on the availability of other prey items in the surrounding environment. Interspecific prey aggregations or “neighborhoods” may therefore affect an individual's vulnerability to predation. We examined the influence of prey neighborhood structure (i.e., the densities and identities of prey neighborhoods) on spatial variation in predation in a multi‐prey system with a primary apex predator. We combined GPS locations of lions (Panthera leo), kill‐site surveys, and spatially explicit density estimates of five species of ungulates for which a significant level of predation was attributable to lions. In addition to the dual influence of predator activity and vegetation, predation risk was attributable to the structure of prey neighborhoods for at least two of the five species of prey. Along with traditionally recognized components of predation (the rate of predator–prey encounters and prey catchability), we encourage ecologists to consider how prey neighborhood structure influences spatial variation in predation risk.
... Bomas are occupied between 1 and 6 months, after which they are abandoned and livestock are moved in a rotational scheme. Over 1 year, bomas transition into nutrient-rich grazing lawns, as dung and urine break-down and enrich the soil (Veblen 2012;Porensky and Veblen 2015). Those grazing lawns are attractive to plains zebra, but are virtually ignored by hartebeest. ...
Mammals are imperiled worldwide. Threats to terrestrial species are primarily from habitat loss or modification, and in some instances from commercial, illegal, or unregulated hunting. Terrestrial species are negatively affected throughout the tropics from deforestation. Threats to marine mammals are related to harvest, strikes in shipping lanes, pollution, and depleted levels of food resources. Hazards to marine species are pronounced in the North Atlantic Ocean, North Pacific Ocean, and oceans and seas flanking southeastern Asia. Protected areas designed to conserve mammals often are too small, too few, poorly delimited or isolated, and too unreliably supported. The new conservation science proposes that human livelihoods be considered alongside traditional preservationist perspectives. For conservation outside of protected areas to succeed, the protection of wild mammals and their habitats should result in benefit to local people, especially in rural or poor communities. Concerns about declining populations of large mammals in North America during the late 19th and early 20th centuries resulted in the institution of regulations that contributed to the recovery of many populations. Today, in North America and Europe, wild populations are thriving and legal hunting is allowed for a number of mammals, something that is less common in many developing countries, where illegal killing remains a threat to conservation. Nevertheless, populations of large mammals are resilient to regulated hunting because of density-dependent processes that result in increased reproduction, survival, and growth rates. Unfortunately, hunting is unregulated for cultural and economic reasons over much of the Earth. We are beginning to see effects of climate change and invasive species on risk of extinction for many species. The future of mammals, however, is entwined ultimately with the size, growth, and resource demands of the human population.
... While nutrient rich grasses are a common feature, species differ through space and time. Porensky and Veblen (2015), for example, observe high densities of Cynodon plectostachyus within glades in central Laikipia, yet this species was not recorded by Young et al. (1995) when working in the same area; instead, Digitaria milanjiana was found to dominate. In Botswana, Cenchrus ciliaris is strongly associated with Iron Age pastoralist settlements (Denbow 1979), yet elsewhere in southern Africa, such locations host anomalous concentrations of woody taxa like Vachellia (Acacia) tortilis within a Burkea africana-dominated background (Blackmore et al. 1990). ...
The spectre of ‘overgrazing’ looms large in historical and political narratives of ecological degradation in savannah ecosystems. While pastoral exploitation is a conspicuous driver of landscape variability and modification, assumptions that such change is inevitable or necessarily negative deserve to be continuously evaluated and challenged. With reference to three case studies from Kenya – the Laikipia Plateau, the Lake Baringo basin, and the Amboseli ecosystem – we argue that the impacts of pastoralism are contingent on the diachronic interactions of locally specific environmental, political, and cultural conditions. The impacts of the compression of rangelands and restrictions on herd mobility driven by misguided conservation and economic policies are emphasised over outdated notions of pastoralist inefficiency. We review the application of ‘overgrazing’ in interpretations of the archaeological record and assess its relevance for how we interpret past socio-environmental dynamics. Any discussion of overgrazing, or any form of human-environment interaction, must acknowledge spatio-temporal context and account for historical variability in landscape ontogenies.
... This heterogeneity can provide niches for a greater variety of species to occupy, thereby increasing the resilience of rangeland to stress such as drought , and benefitting ranchers that enter into incentive-based land stewardships where the maintenance of biodiversity is desired (Reed et al., 2015). Furthermore, the repeated grazing of burned patches can, along with nutrient import from dung, maintain grasses in palatable vegetative states that constitute grazing lawns (Hempson et al., 2015;Porensky and Veblen, 2015), a common occurrence in African savannas. Here grass communities can convert within a few years to stoloniferous, low-growth forms with low C:N ratios, sustaining palatable forage for livestock (Donaldson et al., 2017) and wild herbivores. ...
It is well known that rangelands lose productivity and ecosystem function under excessive rates of livestock stocking, however the role of the spatio-temporal distribution of grazing density remains debated. Multiple studies show that managing grazing for high livestock density has little effect on plant and livestock productivity , yet fewer explore animal behaviour as a mechanism that would explain these observations. We hy-pothesised that increasing cattle grazing densities under equivalent stocking rates will cause animals to concentrate more, spend more time grazing and thereby increase utilisation of forage, and reduce selection for palatable vegetation patches and species. We compared season-long grazing (SLG), four-camp grazing (FCG) and holistic planned grazing (HPG) over three years in an experimental trial in a mesic grassland of South Africa reflecting a range of grazing densities (SLG < FCG < HPG). We measured the spatio-temporal patterns of cattle behaviour, dietary composition, dung trampling, animal productivity, and normalised difference vegetation index (NDVI). The management approach did not change the time allocated to different animal behaviours, trampling of dung, nor the selection for particular plants. HPG cattle grazed at closer distances to one another than SLG but not FCG, and herds were equally concentrated when resting and walking. HPG cattle spent less time in patches of high vegetation NDVI compared to SLG, thereby reducing the spatial heterogeneity of NDVI over time. Cattle gained 0.2 ± 0.02 kg day −1 ha −1 , and this did not differ between management approaches. The HPG approach is costly to set up and is predicted to take twice as long as FCG and SLG to become profitable. Depending on the management goal, HPG could reduce selection for palatable patches, possibly preventing overgrazing and formation of bare patches over the long term. Alternatively, SLG could increase selection for palatable patches and initiate the formation of grazing lawns and, in combination with fire, commonly used in FCG, might enhance biodiversity.
... However, grass is not all of the same quality for herbivores. Green grass in this ecosystem has twice the crude protein content of brown grass 18 . The biomass of green grass was negatively correlated with annual rainfall across ecological classifications (Fig. 2b), and integrated properties had significantly more green grass than livestock properties (Fig. 2c). ...
Globally, most wildlife lives outside of protected areas, creating potential conflicts between the needs of wildlife and the needs of humans. East African savannas epitomize this challenge, providing habitat for wildlife such as giraffes and elephants as well as for people and their livestock. Conflicts over land use are common, leading to the assumption of a necessary trade-off between wildlife and livestock management. Here, we show that the integration of livestock and wildlife in a large region of central Kenya can have ecological benefits, reducing the abundance of ticks and improving forage. These ecological benefits can be complemented by economic ones when property owners derive income both from wildlife through tourism and from livestock through meat and dairy production. Our results suggest that under specific ecological, economic and social conditions, integrating livestock with wildlife can provide benefits for the environment and for human well-being in African savannas. © 2018, The Author(s), under exclusive licence to Springer Nature Limited.
... Nitrogen and carbon isotope ratios are consistently higher in degraded dung deposits than in natural off-site soils, except at Lukenya site GvJm 48 (Fig. 3 Our analyses of micromorphology, mineralogy, and chemical and isotopic composition reveal that elevated levels of nutrients persist for 3,000 years in decomposed dung at Neolithic herder sites in the grasslands of southern Kenya. Our interpretations of the archaeological data are based on ethno-archaeological and ecological studies of contemporary pastoral settlements that show enrichment in weight percentage (wt%) N and 15 N of soil organic matter, grass phytoliths, dung spherulites and mineral nutrients (especially phosphorous and calcium), relative to off-site samples 8,18,21,22 . Nitrogen in cattle and sheep and goat dung is enriched in 15 N because dung is composed of a mixture of both excreted undigested plant material and 15 N-enriched proteinaceous material from the animals themselves 18,22 . ...
We used ranch records and soil analyses to investigate the effects of cattle ranching on phosphorus (P) and nitrogen (N) balances in a humid, tallgrass savanna ecosystem in Tanzania. Over a 41-yr period between 1958 and 1999, the ranch supported an average of 10 435 cattle. These consumed an estimated 571 586 tons (t) of dry matter containing 692 t P and 6 230 t N. Of these nutrients, 162 t of P (23%) and 602 t of N (9.7%) were exported in animals leaving the ranch, while 222 t (32 %) P and 2 364 t of N (38 %) were transferred as excreta to the night corrals. The measured excesses of nutrients in the soil of the corrals were equivalent to 59% of all P and 19% of all N deposited in these areas over 41 yr. Total losses from the pastures amounted to 10.2% of P and 6.6% of N in the top 20 cm of tall grass savanna soil. These losses, especially of P, probably reduced the nutritional quality of the pastures and may have contributed to the reported decline in animal fertility. In addition, they may have promoted the spread of secondary woodland dominated by Vachellia (formerly Acacia) zanzibarica. Three general conclusions can be drawn from this study. First, humid tallgrass savannas on nutrient-poor soils are unsuitable for intensive livestock production. Second, over an extended period the loss of nutrients from cattle pastures can be ecologically significant. Ensuring the sustainability of grazing systems requires measures to counteract this loss, such as the use of shifting night corrals. Third, ranch records, while lacking the precision and detail possible in experimental studies, can provide valuable insights into long-term effects of ranching that would be difficult to obtain by other means.
The grassland biome supports an enormous diversity of life and includes ecosystems used extensively by humans. Although graminoids lend grasslands their characteristic appearance, forbs are largely responsible for their taxonomic, phylogenetic, and functional diversity. In terms of abundance, however, forbs often play a subordinate role relative to graminoids. Yet this may be a relatively recent phenomenon; evidence is mounting that forbs comprised a major part of the richness of, and were abundant in, the extensive and highly productive grasslands of the Pleistocene, the so‐called “mammoth steppe”. As a legacy of their past prevalence under intensive grazing by megafaunal herbivores, we hypothesize that forbs were, and still are, dependent on niche construction by large mammalian herbivores. We suggest that the high species richness of forbs in grasslands globally merits greater research and conservation attention, and management actions tailored to sustain their abundance and diversity.
Miombo woodlands sustainability in east and south-central Africa is threatened by human activities, including overgrazing. This study investigated seasonal variations in rangeland condition in three grazed areas in miombo woodlands in eastern Tanzania. Transect lines were established across the grazing areas, sampling points were identified and marked at every 10% of the length of transect line. Sampling points were categorised in different distances with respect to settlement. The line intercept method was used to collect data on vegetation cover and forage distribution, while herbaceous forage biomass was estimated using a disc pasture meter. A total of 118 different plant species were observed and grasses comprised 40.6% of all herbaceous species. Bothriochloa pertusa, Cynodon plectostachyus, Hyparrhenia rufa and Urochloa mosambicensis grass species dominated miombo grazed areas in various seasons and distances. These perennial grass species are desirable and indicated moderate grazing activities in miombo. Season affected grass cover, herbaceous forage biomass and nutritional composition. Grass cover and forage biomass were at the lowest during late dry season while forage nutritional quality was best during early dry season. Distance from settlement had no effect on grass cover and herbaceous forage biomass. Rangeland condition was generally fair, livestock stocking rate in continuously grazed drylands should be set at the lowest monthly forage biomass in order to ensure grazing land sustainability.
Short duration overnight cattle kraaling in natural rangelands creates nutrients hotspots attractive to a diverse suite of large mammalian herbivores. However, few studies have determined the use of these sites by large mammalian herbivores. We determined the number of animal sightings per day from camera traps and used them as proxies for use of these newly created nutrient hotspots of varying ages (1, 2, 3 and 4 years) and surrounding vegetation. Six mammalian herbivores of different sizes belonging to three feeding guilds viz. grazers (Burchell’s zebra Equus quagga burchelli and warthog Phacochoerus africanus), mixed feeders (impala Aepyceros melampus and African savanna elephant Loxodonta africana africana) and browsers (northern giraffe Giraffa camelopardalis giraffa and greater kudu Tragelaphus strepsiceros) frequently used these nutrient hotspots. The number of sightings per day of mammalian herbivores was determined during three periods of the year (January – wet season; June – early dry season; October – late dry season) to ascertain their use of these nutrient hotspots. In addition, above ground grass biomass and height was measured and related to grazer sightings. Furthermore, we tested if repeated grazing in the newly created nutrient hotspots stimulated grass compensatory growth. All the mammalian herbivores used the newly created nutrient hotspots similarly throughout the year, with impala the most active users. Grazer and browser use of nutrient hotspots was not influenced by their age, while mixed feeders mostly used the one year old sites. Grazer use of nutrient hotspots was not influenced by aboveground grass biomass and height. Repeated clipping (proxy for grazing) resulted in compensatory aboveground grass biomass growth in nutrient hotspots. Impala benefited the most and zebra the least from the creation of nutrient hotspots in natural rangelands. We conclude that creation of nutrients hotspots through short duration overnight kraaling results in rangeland heterogeneity that improves availability of herbivore foraging sites.
Aims
Management of silvo-pastoral systems in planted and natural forests in semi-arid Mediterranean regions often employs seasonal night corrals for animal protection. This management system changes the spatial distribution of animal excreta, resulting in a net transfer of soil mineral resources and their accumulation in the corrals. After abandonment, corrals are colonized by ruderal species, becoming focal sources for their spread in the forest. We aimed to implement a rational management of seasonal sheep corrals based on a better understanding of the vegetation processes occurring in abandoned corrals, in order to alleviate their negative impact in the forest.
Methods
Relationships between temporal changes in the vegetation, the soil seed-bank and levels of soil nutrients were studied in a chronosequence of abandoned sheep corrals and compared to nearby reference plots in planted Eucalyptus forests grazed by sheep in the semi-arid North-Western Negev, Israel. The region has a bi-seasonal Mediterranean climate, with high dominance of annual species in the grazing range.
Important findings
Abandoned sheep corrals were colonized by seeds of ruderals originating in older abandoned corrals. Subsequent successional changes occur at a slow rate, driven by the depletion of soil resources in the abandoned corrals, and were still in progress 20 years after abandonment. Ruderals were gradually replaced, first by taller grasses and followed by short grasses, but most forbs and particularly geophytes did not recover during this period. Recovery of the original herbaceous vegetation in the corrals was through seed dispersal from the surrounding vegetation, not from the original soil seed-bank remaining in the corrals after abandonment. Ruderal species in the grazed, planted forests behave as patch-tracking metapopulations. Their persistency depends on constant creation of new corrals compensating for the gradually dwindling populations in older abandoned corrals, and on the availability of dispersal vectors.
Sub-Saharan Africa (SSA) is home to approximately ¼ of the global livestock population, which in the last 60 years has increased by factors of 2.5-4 times for cattle, goats and sheep. An important resource for pastoralists, most livestock live in semi-arid and arid environments , where they roam during the day and are kept in enclosures (or bomas) during the night. Manure, although rich in nitrogen, is rarely used, and therefore accumulates in bomas over time. Here we present in-situ measurements of N 2 O fluxes from 46 bomas in Kenya and show that even after 40 years following abandonment, fluxes are still~one magnitude higher than those from adjacent savanna sites. Using maps of livestock distribution, we scaled our finding to SSA and found that abandoned bomas are significant hotspots for atmospheric N 2 O at the continental scale, contributing~5% of the current estimate of total anthropogenic N 2 O emissions for all of Africa.
In contrast to a pure cropping system, integrated crop-livestock systems offer a potential for sustainable intensification of pasture-based savanna systems by maintaining vital ecosystem functions (ESF) while providing stable crop yields in a changing environment. In all variations of the mentioned systems, vegetation and animals interact and influence ESFs in different ways and to different extents. However, to date, there is no comprehensive model available to simulate impacts of large-scale savanna land use change (LUC) on food provision and ESFs. We developed a catalogue of required functional model skills for savanna LUC simulation and analysed existing models against this catalogue by scoring. Based on the model scoring, we discuss challenges and opportunities of different model development pathways. Further steps of model integration and coupling are required to simulate interactions with socio-economic decision-making and LUC effects on wildlife.
Nutrient hotspots strongly attract mammalian herbivores in nutrient-poor habitats such as savanna systems. However, little is known about their seasonal importance for mammalian herbivore species, particularly grazers. In addition, no study has fully quantified the potential re-distribution of nutrients into the surroundings of these hotspots. We assessed nutrient hotspot (i.e., grazing lawns and termite mounds) use by herbivores in a Miombo ecosystem of the Issa valley, Tanzania, using dung counts, camera traps and stable isotope analyses over a one year period, from May 2016 to October 2017. We conducted dung counts along four transects each radiating away from ten termite mounds and six grazing lawns as well as in 16 control sites 100 m away from each nutrient hotspot. In addition, we sprayed grasses around five termite mounds with urea and traced the isotopic signature back in grazing herbivore dung. Grazer dung deposition was twice as high in hotspot areas vs control sites. A total of 32 camera stations recorded 244 wildlife encounters, with mammalian herbivores using hotspot areas four times more frequently compared to control plots. Stable isotope analyses highlighted that dung deposited by mammalian grazers around hotspots likely originated from grasses within or close to hotspot areas, indicating that grazers are responsible for maintaining nutrient stability of these hotspots. We, therefore, emphasize the importance of grazing mammal species for the long-term persistence of hotspots and, thus, their contribution to the maintenance of a heterogeneous landscape within the Miombo ecosystem.
Traditional sheep grazing in natural and planted forests in the Mediterranean basin is based on night penning in seasonal corrals, where excreta accumulate instead of being returned to the grazed range. Lack of planning and unawareness of the long-term effect of abandoned corrals is negatively affecting the landscape and grazing value of the forests. We studied the dynamics of soil nutrients in a chronosequence of abandoned sheep corrals in planted Eucalyptus forests in two semi-arid sites in Israel. Dung decomposition was a slow process lasting 5–10 years. Soluble-N, P and K in the soil beneath the dung layer decreased gradually. Yet, 15–20 years after corral abandonment K and P were still 2 to 3 times higher than in the surrounding range, while soluble-N decreased within 10–15 years. Biomass production in the abandoned corrals was 2–3 times higher than in the grazed range up to 20 years after abandonment. Corrals act as sinks of soil nutrients that are lost to the grazed range. We propose that a balance between nutrient inputs (i.e. atmospheric deposition, N-fixation) and outputs (i.e. grazing and night penning) is reached in the grazed range at a low level of soil nutrients, which may constrain vegetation productivity.
Small-scale fertilization experiments have shown that soil nutrients limit plant productivity in many semiarid grasslands and savannas, but linkages among nutrients, grasses, and grazers are rarely studied in an ecosystem context. We used hectare-scale heterogeneity in soil nutrients created by cattle management practices within a geologically homogeneous savanna to examine relationships among soil nitrogen and phosphorus, above-ground net primary production (ANPP), grass nutrient content, and a mixed community of native and domestic herbivores on central Kenyan rangeland. Increasing soil N and P content was consistently associated with increasing plant productivity and rainfall use efficiency in wet, dry, and drought years. A fertilization experiment and analyses of grass N:P ratios across sites indicated that N is the primary limiting nutrient on nutrient-rich glades, whereas N and P co-limit productivity on nutrient-poor bushland sites. Variation in ANPP among patches within the landscape was linearly correlated with consumption rates of large herbivores. Grazing pressure was consistently high (>60% of ANPP) at all but one site in a dry year (1999), and was greater in nutrient-rich glades (73 ± 4% of ANPP) than in nutrient-poor bushland sites (43 ± 7% of ANPP) in a wet year (2001). Grasses of nutrient-rich sites contained sufficient P concentrations to meet requirements for pregnant and lactating ungulates, whereas grasses in nutrient-poor swards were P deficient. Even though native and domestic herbivores selectively used and intensively grazed nutrient-rich sites, productivity on these sites remained high throughout the study. Analyses of nitrogen budgets for nutrient-rich and nutrient-poor sites showed that large herbivores themselves caused a net N input to the former and a net N loss from the latter. Thus, large herbivores not only respond to heterogeneity in soil and plant nutrients across the landscape, but also play a role in maintaining the N-enriched status of highly productive and intensively grazed sites.
In otherwise nutrient-poor savannas, fertile vegetation patches are particularly attractive to ungulates because of the higher-quality food they provide. We investigated forage plants and diet of the common warthog (Phacochoerus africanus) on an abandoned cattle ranch in coastal Tanzania. The forage grasses of highest nutritional quality occurred in former paddock enclosures (bomas) where cattle had been herded at night. In the dry season, grass samples from bomas contained approximately 4 times as much nitrogen and phosphorus as those of the surrounding vegetation. δ15N values of soil and plants also were highest in bomas and decreased significantly with distance, and high δ15N values in feces suggest that warthogs preferentially fed in the vicinity of the former bomas. δ13C values of warthog feces indicate that warthogs ingested on average 83% (77-98%) C4 grasses, with this proportion varying regionally but not seasonally. We conclude that, for medium-sized selective grazers such as warthogs, bomas represent attractive feeding grounds. We also hypothesize that by promoting nutrient turnover in these patchily distributed areas, grazing animals help to maintain them as sources of high-quality forage.
Studies in community ecology are typically conducted over the span of a few years, and results are often interpreted as the product of contemporary processes and interactions. All landscapes have histories, however, and observed patterns of distribution and abundance frequently reflect enduring legacies of past ecological events, the existence and influence of which may not be obvious to investigators. In East Africa, most wildlife occurs outside national reserves and often coexists there with livestock, which are traditionally corralled at night in temporary thorn fence enclosures, or bomas. After being abandoned, bomas develop into nutrient-rich, treeless glades that can persist for more than a century. These hotspots of primary productivity attract both native and domestic large herbivores, but the extent to which their effects cascade to other consumers is unknown. Here, we document positive edge effects of glades on the mean size and growth rates of Acacia trees and show that the density and biomass of arboreal geckos (Lygodactylus keniensis) are elevated near glades and decrease with distance from glades. The edge response of geckos is an indirect effect arising from the positive influence of glades on arboreal arthropod biomass (a trophic effect) and average tree size (a non-trophic effect). By clearing plots of trees to simulate glades, we experimentally demonstrate that these legacy effects arise from the elevated nutrient content of glades as opposed to their distinctive structural features. Finally, we investigated interactions among glade edges, showing that legacy effects are dampened (rather than enhanced) by the presence of other glades nearby. Collectively, our results show that legacy effects of traditional pastoral practices cascade into the treetops, imparting spatial structure across multiple trophic levels in an otherwise homogeneous Kenyan savanna ecosystem.
Areas of locally intense and frequent grazing, or ‘hotspots’, are pervasive features in tropical grasslands and savannas. In some ecosystems, hotspot presence is clearly associated with edaphic factors (e.g., high clay content and elevated soil fertility), such as those that develop in abandoned cattle bomas. Studies in a range of other savanna ecosystems, however, have failed to find intrinsic soil differences between hotspots and the surrounding matrix. Also, it remains unclear to what extent hotspots are associated with specific assemblages of nutrient‐rich plant species, as opposed to being a manifestation of intraspecific variation in nutritive quality. We conducted simultaneous studies in Kruger (South Africa) and Serengeti (Tanzania) National Parks to re‐evaluate the role of edaphic correlates of hotspot occurrence and to test whether intraspecific variation in plant quality occurs across hotspot‐matrix boundaries. We sampled soils and plants in paired hotspot and matrix plots at multiple sites within each ecosystem to test our a priori hypothesis that hotspots would be associated with distinct species assemblages and differences in soil fertility. We found clear hotspot‐matrix differences in foliar N, particularly within species, despite finding no differences in any soil or plant–soil variables, including N mineralization potential and mycorrhizal inoculation levels. We found only weak differences in community composition across the boundary, suggesting that intraspecific variation in foliar N rather than species turnover is mainly responsible for the enhanced nutritive value of hotspot vegetation. We propose that grazer–plant interactions may be stronger drivers of hotspot maintenance in these systems than plant–soil interactions.
Throughout the last decades, agricultural abandonment in European mountain areas has caused changes in traditional livestock management with consequences for semi-natural grassland use and vegetation. In the Western Italian Alps, continuous extensive grazing has become the simplest and the most common system for managing large cattle herds. As a result, limited grazing in many rugged locations has led to an extensive shrub-encroachment of semi-natural grasslands in the sub-alpine and alpine belts. A study was conducted to assess if the provision of mineral mix supplements (MMS): (1) increases the use of steep and shrub-encroached locations by beef cows, and (2) helps restore meso-eutrophic grassland vegetation around supplement-deployment sites. During the summer grazing season, MMS were placed within 10 steep and shrub-encroached areas in two adjacent pastures (364 and 366 ha), and 12 cows were tracked with GPS collars. For each supplement site, a paired control site was identified, and vegetation surve
Throughout the Laikipia ecosystem in Kenya, isolated glades occur within acacia bushland and woodland communities. These glades are at least several decades old. They are reported to be old settlement sites of traditional pastoralists no longer present, and their size, location, and orientation are consistent with the settlement sites of related pastoralists studied elsewhere. The purpose of this study was to document the effects of these glades at the local and landscape levels. Working in central Laikipia, we documented differences in vegetation, animal use, and soils at four of these glades, and at increasing distances from glade edges. Four ''glade specialists'' dominated the plant communities within glades, and were very rare outside of glades. Pennisetum stramineum, one of six glade edge species, formed a ring of dense tall grass around most glade edges. The transition to acacia bushland at the glade edges was not always abrupt (depending on the trait considered), resulting in edge effects that differed in depth and sharpness. Edge depth, defined as the distance required to attain two-thirds of background levels for a trait, ranged from 0 to 200 m. Understory plant species richness and diversity were lowest inside glades, and gradually increased with distance from glades. However, because glades supported species not found elsewhere, the presence of glades increased overall species diversity. The density of wild and domestic large mammal dung was up to 10 times greater inside the glades, and declined with distance from glade edges. Similarly, soil nitrogen, potassium, carbon, calcium, and sodium were greatest inside glades. Soil phosphorus, magnesium, and manganese were not elevated inside glades or within 100 m of glades, but instead were much more abundant in background samples. These glades may be maintained by high densities of large mammals, either through herbivory or through changes in soil chemistry. Glades may be attractive to mammals because of the high quality of food there, or as part of an anti-predator strategy. The result is a relatively permanent community mosaic that increases ecosystem heterogeneity and resource use by domestic and wild animals. The spatial nature of this heterogeneity differs among species, depending on their distributions relative to the glades.
Studies in community ecology are typically conducted over the span of a few years, and results are often interpreted as the product of contemporary processes and interactions. All landscapes have histories, however, and observed patterns of distribution and abundance frequently reflect enduring legacies of past ecological events, the existence and influence of which may not be obvious to investigators. In East Africa, most wildlife occurs outside national reserves and often coexists there with livestock, which are traditionally corralled at night in temporary thorn fence enclosures, or bomas. After being abandoned, bomas develop into nutrient-rich, treeless glades that can persist for more than a century. These hotspots of primary productivity attract both native and domestic large herbivores, but the extent to which their effects cascade to other consumers is unknown. Here, we document positive edge effects of glades on the mean size and growth rates of Acacia trees and show that the density and biomass of arboreal geckos (Lygodactylus keniensis) are elevated near glades and decrease with distance from glades. The edge response of geckos is an indirect effect arising from the positive influence of glades on arboreal arthropod biomass (a trophic effect) and average tree size (a non-trophic effect). By clearing plots of trees to simulate glades, we experimentally demonstrate that these legacy effects arise from the elevated nutrient content of glades as opposed to their distinctive structural features. Finally, we investigated interactions among glade edges, showing that legacy effects are dampened (rather than enhanced) by the presence of other glades nearby. Collectively, our results show that legacy effects of traditional pastoral practices cascade into the treetops, imparting spatial structure across multiple trophic levels in an otherwise homogeneous Kenyan savanna ecosystem.
Small-scale fertilization experiments have shown that soil nutrients limit plant productivity in many semiarid grasslands and savannas, but linkages among nutrients, grasses, and grazers are rarely studied in an ecosystem context. We used hectare-scale heterogeneity in soil nutrients created by cattle management practices within a geologically homogeneous savanna to examine relationships among soil nitrogen and phosphorus, above- ground net primary production (ANPP), grass nutrient content, and a mixed community of native and domestic herbivores on central Kenyan rangeland. Increasing soil N and P content was consistently associated with increasing plant productivity and rainfall use efficiency in wet, dry, and drought years. A fertilization experiment and analyses of grass N:P ratios across sites indicated that N is the primary limiting nutrient on nutrient-rich glades, whereas N and P co-limit productivity on nutrient-poor bushland sites. Variation in ANPP among patches within the landscape was linearly correlated with consumption rates of large her- bivores. Grazing pressure was consistently high (.60% of ANPP) at all but one site in a dry year (1999), and was greater in nutrient-rich glades (73 6 4% of ANPP) than in nutrient- poor bushland sites (43 6 7% of ANPP) in a wet year (2001). Grasses of nutrient-rich sites contained sufficient P concentrations to meet requirements for pregnant and lactating un- gulates, whereas grasses in nutrient-poor swards were P deficient. Even though native and domestic herbivores selectively used and intensively grazed nutrient-rich sites, productivity on these sites remained high throughout the study. Analyses of nitrogen budgets for nutrient- rich and nutrient-poor sites showed that large herbivores themselves caused a net N input to the former and a net N loss from the latter. Thus, large herbivores not only respond to heterogeneity in soil and plant nutrients across the landscape, but also play a role in maintaining the N-enriched status of highly productive and intensively grazed sites.
In African savannas, humans and their livestock leave long-term legacies on the landscape in the form of abandoned livestock bomas (corrals). Once abandoned, bomas develop into nutrient-rich herbivore hotspots characterised by distinctive plant communities. Impacts of bomas, however, extend beyond the boundaries of the boma site itself. This is especially true for woody species which are intensively harvested for boma fencing material and fuel wood. Following boma abandonment, it is not clear how quickly, or to what extent, woody plant communities may change and develop over time. A chronosequence approach was used to investigate the effects of traditional livestock bomas on woody plant communities over time in an Acacia drepanolobium Sjost. savanna in central Kenya. Densities of woody species associated with boma sites that had been abandoned <4, 7–42, and >42 years before were measured. Reductions in densities of the dominant tree, A. drepanolobium, were still detectable after >42 years, especially in the highest impact zones at boma edges (up to 60 m from the boma). Despite these overall reductions, the edge zones of old boma sites had unusually high densities of very large A. drepanolobium trees. Woody species richness increased at edges of newly abandoned bomas, as did densities of the uncommon shrub Lycium europaeum L., and these changes persisted for several decades. These patterns likely result from interactions among species within the woody plant community, as well as interactions with herbivores and edaphic factors. Additional keywords: black cotton soil, glade, kraal, livestock-wildlife interactions, pastoralism.
▪ Abstract Savannas occur where trees and grasses interact to create a biome that is neither grassland nor forest. Woody and gramineous plants interact by many mechanisms, some negative (competition) and some positive (facilitation). The strength and sign of the interaction varies in both time and space, allowing a rich array of possible outcomes but no universal predictive model. Simple models of coexistence of trees and grasses, based on separation in rooting depth, are theoretically and experimentally inadequate. Explanation of the widely observed increase in tree biomass following introduction of commercial ranching into savannas requires inclusion of interactions among browsers, grazers, and fires, and their effects on tree recruitment. Prediction of the consequences of manipulating tree biomass through clearing further requires an understanding of how trees modify light, water, and nutrient environments of grasses. Understanding the nature of coexistence between trees and grass, which under other ci...
In sub-Saharan Africa, the widespread practice of corralling livestock overnight in thorn-scrub “bomas” creates nutrient-enriched patches within rangelands that can subsequently support unique plant communities for decades to centuries after boma abandonment. These nutrient-rich patches (glades) may be preferentially used by native ungulates that coexist with livestock. To evaluate the potential link between cattle management via bomas and habitat for impala (Aepyceros melampus), I examined seasonal patterns of habitat selection by impala and landscape variation in grass nutrient content on a commercial cattle ranch in central Laikipia, Kenya. Studies using automated, infrared camera monitors showed that impala selected nutrient-rich glades 2.6 times more frequently than surrounding Acacia bushland habitat during dry seasons, and 9.6 times more frequently during wet seasons. Significantly greater impala presence in glade versus bushland habitat during dry seasons suggests that impala presence may be related to reduced predation risk in shrub-free glades. The large, significant increase in impala presence in glades from dry to wet seasons suggests that impala distribution also is linked to the availability of nutrient-rich forage. In particular, grass nutrient analyses showed that wet-season phosphorus (P) concentrations in grasses throughout the bushland landscape (x̄ = 2,125 mg P/kg dry matter, varying from 1,789 to 2,922 mg P/kg across topographic positions and from 1,508 to 3,215 mg P/kg among grass species) were below recommended levels for pregnant and lactating ruminants, while mean P concentrations in glade grasses (x̄ ± SE = 5,346 ± 2.92 mg P/kg) exceeded recommended levels. Results suggest that management to increase the relocation rate and distribution of current cattle bomas can have a positive, long-term effect on the local distribution and abundance of impala.
The impact of livestock grazing on soil nutrients and vegetation parameters was studied in dry montane steppes of southern Mongolia in order to assess the risk of habitat degradation. Data were collected along transects radiating away from permanent water sources. Dung unit density counts revealed gradients of livestock activity, but utilization belts around water sources overlapped, indicating that pastoral land use affects the entire landscape. Dung unit counts corresponded to gradients in soil nutrient parameters (C, N, P), which significantly decreased with distance from the wells. However, no significant correlation was observed for plant species richness and vegetation composition with distance from water source. This indicates that soil parameters and livestock grazing exert a relatively smaller influence on the vegetation than the high inter-annual variability in precipitation. Therefore, the ecosystem at the study site was found to react in a non-equilibrium way, which suggests that the risk of degradation is low, at least insofar as plant community composition is concerned.
Questions: What is the observed relationship between plant species diversity and spatial environmental heterogeneity? Does the relationship scale predictably with sample plot size? What are the relative contributions to diversity patterns of variables linked to productivity or available energy compared to those corresponding to spatial heterogeneity?
Methods: Observational and experimental studies that quantified relationships between plant species richness and within-sample spatial environmental heterogeneity were reviewed. Effect size in experimental studies was quantified as the standardized mean difference between control (homogeneous) and heterogeneous treatments. For observational studies, effect sizes in individual studies were examined graphically across a gradient of plot size (focal scale). Relative contributions of variables representing spatial heterogeneity were compared to those representing available energy using a response ratio.
Results: Forty-one observational and 11 experimental studies quantified plant species diversity and spatial environmental heterogeneity. Observational studies reported positive species diversity-spatial heterogeneity correlations at all points across a plot size gradient from ∼1.0 × 10−1 to ∼1.0 × 1011 m2, although many studies reported spatial heterogeneity variables with no significant relationships to species diversity. The cross-study effect size in experimental studies was not significantly different from zero. Available energy variables explained consistently more of the variance in species richness than spatial heterogeneity variables, especially at the smallest and largest plot sizes.
Main conclusions: Species diversity was not related to spatial heterogeneity in a way predictable by plot size. Positive heterogeneity-diversity relationships were common, confirming the importance of niche differentiation in species diversity patterns, but future studies examining a range of spatial scales in the same system are required to determine the role of dispersal and available energy in these patterns.
The aim of this study was to analyze the depletion of soil nutrients with time on abandoned kraals in a peri-urban area of Botswana. Active kraals are enriched with nutrients through the accumulation of animal droppings and this study was aimed at assessing how long the impact of this soil nutrient enrichment persists after kraal abandonment. A total of 25 disused kraals, that had been abandoned for periods ranging from 1 to 45 years were sampled. The soil parameters analyzed included particle size distribution (%), bulk density (g/cm 3), pore space (%), moisture content (%), pH in water and KCl solution, EC (µS/cm), organic matter (%), CEC (meq/100g), exchangeable Ca ++ (cmol c /kg), Mg ++ (cmol c /kg), K + (cmol c /kg), Na + (cmol c /kg), nitrogen [NH 4 -N (mg/kg), NO 3 -N (mg/kg), TKN (%), and Olsen P (mg/kg). Results showed that soil nutrient concentrations on abandoned kraals generally were significantly higher than at the control sites. Soil nutrient concentrations decreased with time as abandoned kraals retrogressed towards their pre-kraal conditions. However, the effects of soil nutrient enrichment from animal wastes persist long after kraal abandonment. For example, soil Olsen P, Ca ++ and Mg ++ levels in kraal sites that had been abandoned for over 45 years were still significantly higher than in the control sites. In a pastoral system such as is practiced in Botswana where kraal manure is not used as soil amendment, the whole ecosystem suffers as soil nutrients are transferred and concentrated at isolated spots (kraals).
Cattle are usually thought of as a threat to biodiversity. In regions threatened by exotic species invasion and lacking native wild grazers, however, cattle may produce the type of disturbance that helps maintain diverse communities. Across 72 vernal pools, I examined the effect of different grazing treatments (ungrazed, continuously grazed, wet-season grazed and dry-season grazed) on vernal-pool plant and aquatic faunal diversity in the Central Valley of California. After 3 years of treatment, ungrazed pools had 88% higher cover of exotic annual grasses and 47% lower relative cover of native species than pools grazed at historical levels (continuously grazed). Species richness of native plants declined by 25% and aquatic invertebrate richness was 28% lower in the ungrazed compared with the continuously grazed treatments. Release from grazing reduced pool inundation period by 50 to 80%, making it difficult for some vernal-pool endemic species to complete their life cycle. My results show that one should not assume livestock and ranching operations are necessarily damaging to native communities. In my central California study site, grazing helped maintain native plant and aquatic diversity in vernal pools.
Livestock-wildlife interactions in rangelands are often viewed in terms of competition, but livestock and native ungulates can also benefi t each other through long-term modifi cations of rangeland habitats. Here we synthesize research on rangelands in central Laikipia focusing on two types of cattle-wildlife interactions that have implica-tions for their long-term coexistence. The fi rst interaction occurs via redistribution of soil nutrients within the ecosystem, which is a consequence of the use of bomas (temporary corrals) to manage livestock. Our studies on two different soil types show that rotational boma management creates hectare-scale patches in the landscape that are enriched in soil and plant nutrients and persist for decades to centuries. In both of the predominant soil types in Laikipia, forage phosphorus content is low relative to ungulate demands during peak lactation. Nutrient-rich boma sites (hereafter referred to as glades) provide a key wet-season forage resource of nutritional suffi ciency for lactation. Our studies further show that a wide range of native ungulates selectively use glades relative to surrounding nutrient-poor habitats. Impala (Aepyceros melampus) in particular show intensive use of glades on sandy soils and are rare in portions of the landscape lacking glades. A second important pathway for cattle-wildlife interaction occurs through the infl uence of native browsing ungulates on woody vegetation. Shrub and tree cover has been increasing in Laikipia over the past century, followed by increases in native browsers in recent decades on ranches where wildlife are allowed to coexist with cattle. Our exclosure experiments in central Laikipia indicate that native browsers suppress shrub encroachment on both dominant soil types. However, the strength of browser effects are three to seven times greater on sandy soils, where two browsers, dik-dik and elephants, are both abundant, compared to heavy clay soils, where elephants are the only dominant browser. In the clay soils, native browsers still exert a signifi cant infl uence on dynamics of the domi-nant tree, Acacia drepanolobium, and suppress encroachment by subdominant shrub species. Browser effects on woody vegetation likely enhance forage production for cattle and maintain open habitats favored by native grazers for predator avoidance. Taken together, our studies indicate that boma rotation and browser control of shrub encroach-ment are key interaction pathways that promote cattle-wildlife coexistence in the Ewaso ecosystem.
1. Through their effects on plant communities, herbivores can exert strong direct and indirect effects on savanna ecosystems and have the potential to create and maintain savanna landscape heterogeneity. Throughout much of sub‐Saharan Africa, periodic creation and abandonment of livestock corrals leads to landscape mosaics of long‐term ecosystem hotspots that attract both cattle and large ungulate wildlife.
2. The development and maintenance of vegetation in these types of hotspots may be controlled in part by herbivory. Cattle and wildlife may have different, potentially contrasting effects on plant succession and plant–plant interactions. We ask how cattle and wild herbivores affect the maintenance and vegetation development of corral‐derived landscape heterogeneity (0.25–1.0 ha treeless ‘glades’) in Laikipia, Kenya, through their effects on long‐term successional and short‐term plant–plant dynamics.
3. We used the Kenya Long‐term Exclosure Experiment to exclude from glades different combinations of cattle, large ungulate wildlife (i.e. zebras, gazelles and other antelopes), and mega‐herbivore wildlife (i.e. giraffes and elephants). We first assessed long‐term changes in cover of the dominant grass species, Cynodon plectostachyus and Pennisetum stramineum (the early‐ and late‐dominant species, respectively). We then used a neighbour removal experiment to test the effects of different herbivores on competition and facilitation between the two glade grass species.
4. In the long‐term experiment, we found that large ungulate wildlife reinforced landscape heterogeneity over time by helping maintain glades in their early C. plectostachyus ‐dominated form. Cattle and mega‐herbivore wildlife, on the other hand, appeared to reduce the positive effects through forage preference for C. plectostachyus .
5. In the neighbour removal experiment, we found that each grass species benefited from facilitation when it was the preferred forage for the dominant grazer. Facilitation of C. plectostachyus by P. stramineum was strongest when cattle co‐occurred with wildlife, whereas facilitation of P. stramineum by C. plectostachyus was strongest when cattle were absent.
6. Synthesis . Our results demonstrate that different combinations of cattle and wildlife have different effects, largely via contrasting forage preferences, on the persistence of landscape heterogeneity in this savanna landscape. More generally, we provide evidence for contrasting effects of cattle and wildlife on short‐term plant interactions (facilitation) and successional processes within the herbaceous plant community.
Woody vegetation is distributed patchily in many arid and semi-arid ecosystems, where it is often associated with elevated
nitrogen (N) pools and availability in islands of fertility. We measured N availability and δ15N in paired blue-oak versus annual grass dominated patches to characterize the causes and consequences of spatial variation
in N dynamics of grassland-savanna in Sequoia-Kings Canyon National Park. We found significantly greater surface soil N pools
(0–20cm) in oak patches compared to adjacent grass areas across a 700m elevation gradient from foothills to the savanna-forest
boundary. N accumulation under oaks was associated with a 0.6‰ depletion in soil δ15N relative to grass patches. Results from a simple δ15N mass balance simulation model, constrained by surface soil N and δ15N measured in the field, suggest that the development of islands of N fertility under oaks can be traced primarily to enhanced
N inputs. Net N mineralization and percent nitrification in laboratory incubations were consistently higher under oaks across
a range of experimental soil moisture regimes, suggesting a scenario whereby greater N inputs to oak patches result in net
N accumulation and enhanced N cycling, with a potential for greater nitrate loss as well. N concentrations of three common
herbaceous annual plants were nearly 50% greater under oak than in adjacent grass patches, with community composition shifted
towards more N-demanding species under oaks. We find that oaks imprint distinct N-rich islands of fertility that foster local
feedback between soil N cycling, plant N uptake, and herbaceous community composition. Such patch-scale differences in N inputs
and plant–soil interactions increase biogeochemical heterogeneity in grassland-savanna ecosystems and may shape watershed-level
responses to chronic N deposition.
An investigation of the long-term effects of livestock grazing on the spatial distribution of plant nutrients was conducted in the Sahelian region of West Africa. The study area was located along the transhumance corridor used for at least the past century by a long-established population of agropastoralists in central Mali. Spatial variation of plant and soil chemistry across eighteen sites was investigated with respect to a grid, whose axes are defined by distance from a pan from which livestock disperse to graze primarily during the early dry season (D1) and by distance from the nearest of three pans used primarily during the rainy season (D2). Particle size distribution, pH, total C, N, and P of surface soil (0-10 cm) was determined for four composite samples collected at eleven of the eighteen ecological sites. Elemental analysis (N, P, Ca, Mg, K, Mn, Fe, Zn, Cu) was performed on above-ground tissues samples (excluding seeds) of the three most common grasses and the most common legume collected at all eighteen sites at the end of the rainy season. Results demonstrate that long-term grazing movements can, over the long-term, affect nutrient availability over wider spatial scales (5 km radii) than previously observed by shorter-term studies. Soil and plant chemistry were found in general to be most affected by the historic gradient of cattle presence during the rainy season (D2). Controlling for soil C and coarse sand fraction, soil pH was found to decline with D2 (-0.5 pH units per km D2) and to a lesser extent D1 (-0.15 pH units per km D1), a finding that cannot be explained solely by a consideration of local geomorphology. The pH gradient was found to significantly affect micronutrient concentrations in plant tissues. Phosphorus (P) concentrations of plant tissue were found to decrease with D2. The increase in P-availability near rainy-season encampments should result from P-release from Al-complexes at higher pH and/or by the redistribution of P from outlying zones towards rainy-season encampments.
(1) A comparison of the vegetation and soil was made around two boreholes differing in cattle density and exploitation period. (2) Increased grazing and trampling pressure around the borehole has caused a vegetation zonation with a species-poor zone in the immediate vicinity of the borehole, followed by thickets with Acacia species and Dichrostachys cinerea, transitional to tree savanna. (3) The creation of the artificial water points has caused an increase in soil nutrients near the borehole due to deposition of dung and urine, the amount dependent on cattle density and borehole age. (4) The increased soil fertility is reflected in the nutrient content of the herbs and trees near the boreholes. (5) A nutrient balance demonstrated that overgrazing severely affected the phosphorus balance of the savanna ecosystem.
Mechanical and chemical methods used historically to rejuvenate sagebrush-steppe landscapes are cost prohibitive. A low-cost alternative is to fashion systems of management in which locally adapted animals use sagebrush as fall and winter forage to reduce feeding costs and to enhance the growth of grasses and forbs during spring and summer. We evaluated the practicality of fall browsing of sagebrush (Artemisia tridentata ssp. tridentata, ssp. wyomingensis) by cattle. To do so, we assessed 1) the foraging behavior and body weights of cattle with varying levels of experience browsing sagebrush, and 2) the ensuing responses of sagebrush, grasses, and forbs to cattle grazing. In spatially and temporally replicated trials from 2007 to 2009, cattle were challenged to eat sagebrush. Pregnant cows with calves (2007 and 2008), bred yearling heifers (2008), and first-calf heifer/calf pairs (2009), supplemented with protein and energy, learned to eat sagebrush as a significant portion of their diet (up to 63% of scans recorded during grazing). Experienced animals consistently ate more sagebrush and lost less weight, or gained more weight, than naive animals in 2008 and 2009 (P < 0.05). Cover, production, and percent composition of grasses and forbs maintained or dropped slightly from 2007 to 2008 but then rebounded sharply in 2009 to much greater levels than in 2007 or 2008 (P < 0.05). A corresponding reduction in shrub cover, production, and percent composition accompanied the increase in forbs and grasses (P < 0.05). Our research suggests grazing by cattle during fall and winter can be effective, biologically and economically, and can lead to habitat renovation and resilience by creating locally adapted systems of management in ways that landscape manipulations with chemical and mechanical treatments or prescribed fire cannot.