Population trends of large non-migratory wild herbivores and livestock in the Masai Mara ecosystem, Kenya, between 1977 and 1997

The total of all non-migratory wildlife species in the Masai Mara ecosystem has declined by 58% in the last 20 years. This decline ranges from 49% in small brown antelopes to 72% in medium brown antelopes. In individual wildlife species, the decline ranges from 52% in Grant's gazelle to 88% in the warthog. Declines of over 70% have been recorded in buffalo, giraffe, eland and waterbuck. Only elephant, impala and ostrich have not shown any significant decline or increase. Overall, there has not been any significant difference in decline of all wildlife population sizes inside and outside the reserve, except for Thomson's gazelle and warthog. Livestock have not significantly declined over the entire analysis period. However, livestock and cattle populations significantly declined during the 1983–88 period. Donkey declined by 67%, while shoats (goats and sheep) remained stable. In the case of wildlife, land use and vegetation changes, drought effects and poaching are considered to be among the potential factors that may have been responsible for the decline; the decline in livestock during the 1983–84 period was probably due to drought effects.     

Restoration of riparian meadows degraded by livestock grazing: above- and belowground responses

Riparian meadows in the western US are highly productive areas withinthe riparian corridor that have been extensively utilized for livestock grazingand that are often degraded. This study aimed to increase our understanding ofboth the functional responses and restoration potential of mesic meadow systemsin central Nevada, USA. Nitrogen addition and clipping treatments were used toexamine grazing effects, while aeration and revegetation were included toevaluate potential restoration treatments. Belowground response was determinedby examining gravimetric soil water content and rooting depth and activity.Aboveground response was determined for two key mesic meadow species,Carex nebrascensis and Poa pratensis,by quantifying gas exchange and water relations. Large yearly and seasonaldifferences among water tables largely determined the rooting activity anddepthin these mesic meadows and influenced treatment responses. Little rootingactivity occurred within or at the surface of the water table and rooting depthincreased as water table level lowered during the growing season. In general,nitrogen addition decreased rooting activity and depth relative to controls. Itresulted in less negative water potentials and photosynthetic rates that werehigher early in the growing season, but lower later in the growing season. Theeffects of nitrogen addition could be attributed to accelerated phenology andearlier senescence. Clipping resulted in less negative plant water potentialsinCarex and Poa, andPoa had higher photosynthetic rates immediately afterclipping but only for certain dates and comparisons. Aeration increased rootingactivity and depth where there was no confounding effect of water table. Also,predawn and midday water potentials were generally less negative forCarex and Poa in aerated plots.Establishment on the revegetation plots was dominated by annual and early seralspecies and, consequently, these plots exhibited reduced rooting depth andactivity early in the growing season and high root turnover. Results indicatethat water table depth and its effects on soil water are dominant factors indetermining the functional processes and recovery potentials of these riparianmeadows. Clipping had minimal effects on above- and belowground responses,perhaps because clipping was performed late in the growing season after plantshad begun to senescence. Nitrogen addition decreased rooting activity andaltered phenology, indicating deleterious effects. Aeration was effective atovercoming some of the negative affects of overgrazing and may be an effectiverestoration treatment. However, revegetation may have limited potential due toestablishment constraints of the dominant species.     

Assessment of the woody vegetation of Ol Choro Oiroua, Masai Mara, Kenya

The woody vegetation of the Ol Choro Oiroua Wildlife Management and Conservation area was surveyed. The species present, their size and the vertical distribution of their canopy were recorded. These parameters were then used to determine the percentage cover of woody vegetation at different heights, and the potential productivity of the trees and shrubs in terms of the available browse material. The survey data were converted to Browse Tree Equivalents, Leaf Dry Mass and a Canopy Sub-habitat Index, using the Browse Estimate from the Canopy Volume (B ecvol ) program. These parameters were next used to assess and predict the potential production of available browse material. The assessment established permanent observation plots for browse productivity estimates, and to serve as a basis for monitoring the encroachment or decline of woody species in the region.     

Status of the Mara Woodlands in Kenya

The woodlands of the Masai Mara National Reserve in Kenya have suffered dramatic declines over four decades as a result of elephant and fire pressure. This study examined the current status of woody resources in the Reserve and browse pressure thereon, using both classification (TWINSPAN) and ordination (DCA) techniques. From 333 widespread regular plots used to survey the vegetation, a total of 62 woody species were identified. Thirteen woody habitats were identified on the basis of species composition, varying from species‐rich closed thickets and forest to less diverse open grasslands. A NW/SE stratification of the more open habitats was observed, possibly as a result of differences in soils, rainfall and drainage. Both plant density and diversity were lower than in communal and privately managed areas outside the Reserve. Moreover, browser pressure was substantially higher than that observed previously in the ecosystem, and suggests increased competition for scarcer woody resources within the Reserve. This has implications for the management of the ecosystem as a whole. As woodland and thickets continue to decline, long‐term monitoring should expand to encompass the wider habitat diversity of the open grasslands and unprotected areas where much of the regeneration potential resides.     

Trajectories of change: riparian vegetation and soil conditions following livestock removal and replanting

Riparian zones provide critically important ecological functions, including the interception of nutrients and sediments before they enter waterways. Consequently, riparian zones, and the vegetation they support, are often considered as an important ‘final buffer’ between waterways and adjacent land. In agricultural ecosystems, riparian zones are therefore increasingly recognized as an important component of strategies aimed at minimizing the flow of nutrients and sediments into waterways. Accordingly, riparian zones are increasingly afforded protection and are targeted for restoration. Here we present results of a study in which we aimed to identify patterns of change in soil and vegetation properties in riparian zones, under different management regimes, adjacent to tributary streams in one of south‐eastern Australia's main agricultural regions. We compared riparia that were heavily impacted by agricultural activities, were in remnant condition or had undergone some restoration activities and were thus in a transitional state. There was an increase in plant cover and soil C concentration between impacted through to remnant sites, with transitional sites intermediate, suggesting that improvements in soil conditions were becoming evident following restoration activities. In our assessment of soil physicochemical properties we investigated the relationships between riparian condition and soil properties, taking into account the influence of adjacent land use on these relationships. Importantly, the concentrations of NO₃^‐ and plant available P in riparian surface soils were more or less influenced by concentrations in the adjacent land depending upon riparian condition. This will, in turn, have consequences for nutrient inputs into streams. This study emphasizes that riparian zones need to be managed within their wider landscape context. Furthermore, the results of this study will inform efforts seeking to minimize impacts of agricultural activities on waterways, through the conservation and/or restoration of riparian ecosystems.     

Influence of livestock grazing on vegetation in a saline area in Northeast Thailand

The influence of grazing by water buffalo (Bubalas bufalis) and cattle (Bos taurus) was estimated for vegetation inside and outside cages in a saline area at Khon Kaen, Northeast Thailand. The home range of water buffalo and cattle shifted in response to the period of rice cultivation: during the rice-growing season these animals grazed on roadsides and abandoned places such as the study area; after rice harvest they grazed mainly rice stubble on the paddy. The vegetation in the study area was divided into three types: 1) dominated by the annual grassesChloris barbata andIschaemum rugosum; vegetational cover and plant height in the cage increase due to the increase of these grasses; 2) thorny shrub patch ofMaytenus mekongensis; other species in this patch almost died a year after experimental elimination of this shrub; this salt-tolerant shrub not only protected the co-existing species from grazing, but also suppressed salt accumulation; 3) almost pure stand ofPanicum repens; livestock preferred this perennial grass over others. Electrical conductivity (EC) of surface soil did not increase under the vegetation protected from grazing. Litter and other organic matter in the soil suppressed the upward movement of brine. Grazing led to an increase of bare ground where NaCl accumulated, and modified the heterogeneity of vegetation, which was reflected in the degree of salt accumulation.     

The effects of fire and grazing pressure on vegetation cover and small mammal populations in the Maasai Mara National Reserve

An extensive study of vegetation changes as a consequence of fire and grazing pressure and their effect on small mammal populations inside the Maasai Mara National Reserve, Kenya, was carried out during May–June 1997. Comparison of vegetation maps from 1979 and 1998 suggested that vegetation in 46% of the Reserve area converted from shrubland to grassland, possibly as a result of fire and grazing pressure. We tested the hypothesis that in areas with high fire and grazing impact the population of small mammals was negatively affected. A low density of rodents was recorded in all habitats except in areas of human activity, where artificial resources are constantly present. Capture efforts were unsuccessful in grasslands. Our results confirm those of Norton‐Griffiths (1979) and Dublin (1995) , i.e. that fire and grazing pressure impact the vegetation of the Serengeti–Mara ecosystem and limit the natural regeneration of woodlands. This indirectly affects the small mammal community, which is limited in its long‐term establishment.     

Comparative changes in density and demography of large herbivores in the Masai Mara Reserve and its surrounding human-dominated pastoral ranches in Kenya

Wildlife habitats in pastoral lands adjoining protected areas in east African savannas are getting progressively degraded, fragmented and compressed by expanding human populations and intensification of land use. To understand the consequences of these influences on wildlife populations, we contrasted the density and demography of 13 wild and three domestic large herbivores between the Masai Mara National Reserve and the adjoining pastoral ranches using aerial surveys conducted in the wet and dry seasons during 1977–2010. Species of different body sizes and feeding styles had different densities between landscapes and seasons. Small-sized herbivores, requiring short, nutritious grasses, and browsers were more abundant in the ranches than the reserve in both seasons. Medium-sized herbivores moved seasonally between landscapes. Larger-bodied herbivores, requiring bulk forage but less susceptible to predation, were more abundant in the reserve than the ranches. The proportions of newborn warthog (Phacochoerus africanus) and juvenile topi (Damaliscus korrigum) were higher in the ranches, with shorter grasses and lower predation risk than in the reserve. These results suggest that pastoral lands adjoining protected areas in African savannas are important as seasonal dispersal and breeding grounds for wild herbivores. However, human population growth and dramatic land use changes are progressively degrading wildlife habitats in pastoral areas, thus restricting the seasonal wildlife dispersal movements between the protected areas and adjoining pastoral lands. Conservation efforts should focus on (1) creating and maintaining functional heterogeneity in protected areas that mimic moderate pastoral grazing conditions to attract small and medium-bodied grazers and (2) securing dispersal areas, including corridors, to ensure continued seasonal large herbivore movements between protected and pastoral systems.     

Synergistic influences of introduced herbivores and fire on vegetation change in northern Patagonia,Argentina

Question: We investigated how cattle and European hares, the two most widespread exotic herbivores in Patagonia, affect species composition, life‐form composition and community structure during the first 6 years of vegetation recovery following severe burning of fire‐resistant subalpine forests and fire‐prone tall shrublands. We asked how the effects of introduced herbivores on post‐fire plant community attributes affect flammability of the vegetation. Location: Nahuel Huapi National Park, northwest Patagonia, Argentina Methods: We installed fenced plots to exclude livestock and European hares from severely burned subalpine forests of Nothofagus pumilio and adjacent tall shrublands of N. antarctica. The former is an obligate seed reproducer, whereas the latter and all other woody dominants of the shrubland vigorously resprout after burning. Results: Repeated measures ANOVA of annual measurements over the 2001‐2006 period indicate that cattle and hare exclusion had significant but complex effects on the cover of graminoids, forbs, climber species and woody species in the two burned community types. Significant interactions between the effects of cattle and hares varied by plant life forms between the two communities, which implies that their synergistic effects are community dependent. Conclusions: Following severe fires, the combined effects of cattle and hares inhibit forest recovery and favour transition to shrublands dominated by resprouting woody species. This herbivore‐induced trend in vegetation structure is consistent with the hypothesis that the effects of exotic herbivores at recently burned sites contribute to an increase in the overall flammability of the Patagonian landscape.     

The impact of livestock grazing on the spatial pattern of vegetation in north-eastern Patagonia,Argentina

Background: The occurrence of shrub patches, alternating with either bare soil or low herbaceous cover, is a common feature in arid and semi-arid shrublands throughout the world. This patchy pattern of vegetation may result from water limitation, modulated by plant interactions; grazing (offtake and tramping) by livestock may cause further patchiness vegetation structure.

Aims: We hypothesised that vegetation patchiness in the semi-arid shrublands of north-eastern Patagonia would be increased by livestock grazing, but not by positive interactions between adult plants of shrubs and grasses.

Methods: We compared vegetation cover and pattern at three grazing intensities (exclosure, light and heavy grazing) and measured the growth of a representative shrub and grass in the presence and absence of the other to quantify the role of plant-to-plant interactions and its interaction with grazing for vegetation structure.

Results: In the grazing exclosure and in moderately grazed areas, vegetation cover among shrub patches was larger, whereas the top cover of shrubs was lower than in the heavily grazed areas. We did not find any evidence of positive interactions between shrub and grass life forms.

Conclusions: Our results were consistent with the hypothesis that livestock grazing increased the formation of patchy vegetation cover in arid and semi-arid shrublands.     

Arid vegetation in disequilibrium with livestock grazing: Evidence from long‐term exclosures

In recent decades, the conventional equilibrium paradigm for explaining rangeland vegetation dynamics has been challenged. Proponents of an alternative non‐equilibrium paradigm argue that in variable rangeland environments, external climatic events are critical to vegetation dynamics and there is little opportunity for plant–herbivore interactions to reach equilibrium. Understanding which paradigm more effectively describes an ecosystem has important consequences for management. In particular, some authors have argued that a focus on reducing stocking rates in non‐equilibrium systems may be futile, and management should be opportunistic in response to unpredictable rainfall events. We measured herbaceous biomass and plant species richness and abundance at five 14‐year exclosures on Innamincka Regional Reserve. Four were situated in the dunefields land system, and one on the Cooper Creek floodplain. We did not detect any significant differences between grazed and ungrazed treatments in total species richness or abundance, life form richness or abundance, or herbaceous biomass. Only one species, Portulaca oleracea, showed differences in abundance between treatments at more than one site, but the direction of these differences was not consistent. These results suggest that the non‐equilibrium paradigm more accurately describes vegetation dynamics in the dunefields and floodplains of north‐eastern South Australia. It is possible that some species had been lost from the study area prior to the establishment of the exclosures, thereby precluding recovery with protection from grazing; however, a regional analysis of the flora reveals little evidence of this. We argue that the dominance of ephemeral species confers resilience by limiting the development of strong feedbacks between grazing intensity and vegetation dynamics. Current grazing practices seem consistent with the conservation of plant species diversity across the dunefields and floodplains. Future studies should focus on the impacts of cattle grazing on areas of the landscape dominated by palatable perennials, as well as the small number of rare and potentially grazing‐sensitive species identified.     

Rapid, landscape scale responses in riparian tundra vegetation to exclusion of small and large mammalian herbivores

Productive tundra plant communities composed of a variety of fast growing herbaceous and woody plants are likely to attract mammalian herbivores. Such vegetation is likely to respond to different-sized herbivores more rapidly than currently acknowledged from the tundra. Accentuated by currently changing populations of arctic mammals there is a need to understand impacts of different-sized herbivores on the dynamics of productive tundra plant communities. Here we assess the differential effects of ungulate (reindeer) and small rodent herbivores (voles and lemmings) on high productive tundra vegetation. A spatially extensive exclosure experiment was run for three years on river sediment plains along two river catchments in low-arctic Norway. The river catchments were similar in species pools but differed in species abundance composition of both plants and vertebrate herbivores. Biomass of forbs, deciduous shrubs and silica-poor grasses increased by 40–50% in response to release from herbivory, whereas biomass of silica-rich grasses decreased by 50–75%. Hence both additive and compensatory effects of small rodents and reindeer exclusion caused these significant changes in abundance composition of the plant communities. Changes were also rapid, evident after only one growing season, and are among the fastest and strongest ever documented in Arctic vegetation. The rate of changes indicates a tight link between the dynamics of productive tundra vegetation and both small and large herbivores. Responses were however not spatially consistent, being highly different between the catchments. We conclude that despite similar species pools, variation in plant species abundance and herbivore species dynamics give different prerequisites for change.     

Litter input from riparian vegetation to streams: a case study of the Njoro River,Kenya

Allochthonous coarse particulate organic matter (CPOM) input into the Njoro River was measured between January and June 1998 at two contrasting sites: open-canopy and closed-canopy sites. Bank runoff and aerial drift traps were used for collecting CPOM inputs over periods of two weeks. Collected litter was sorted into four categories: leaves, fruits, wood and plant fragments. Monthly input ranged from 77 to 228 g ash free dry weight m^–1 for bank runoff input and from 64 to 129 g ash free dry weight m^–2 for aerial input. The highest input of 228 g ash free dry weight m^–1 was recorded in May at the closed-canopy site. Wood, fruits and plant fragments of particle size >100 m contributed a mean ± SE of 60±9% of the total inputs with the rest from leaf litter. The closed-canopy site had higher inputs (P<0.05) of bank and aerial input than the open canopy site. There was no relationship between total bank runoff input and rainfall (r _s = 0.08), however, total aerial input increased with decrease in rainfall (r _s = – 0.59). There were differences between inputs from different plant species (P<0.05) that ranked in the following order: Syzygium cordatum > Rhus natalensis > Pittosporum viridiflorum > Vangueria madagascariensis. Removal of riparian vegetation from the banks of the Njoro River would alter the quantity and quality of the litter and reduce CPOM inputs to the river and to a downstream lake with attendant consequences to the energy budget of biocoenoses in the two ecosystems.     

Habitat preference of the striped legless lizard: Implications of grazing by native herbivores and livestock for conservation of grassland biota

Across the globe, many species of reptile are threatened with extinction, with changes in grazing pressure as a significant factor in their decline. Few studies have investigated the role of native herbivores, yet studying natural grazers may provide insight into natural grazing regimes, not apparent in studies of domestic livestock. In this study, we investigate the habitat requirements of a threatened Australian grassland reptile, the striped legless lizard, Delma impar, in grasslands grazed by a native herbivore, the eastern grey kangaroo Macropus giganteus. Delma impar appears sensitive to habitat change resulting from altered grazing intensity, but a lack of information hinders implementation of appropriate grazing regimes. To address this gap, we investigated habitat preferences of D. impar at multiple spatial scales across a grazing gradient. We found that the occurrence of D. impar was not affected by the size of grassland remnants, but was negatively related to the density of native grazers. This result was likely a consequence of the negative effect of high grazing intensity on grass structural complexity, as the probability of encountering a D. impar was positively related to grass structural complexity at the fine scale (1 m²). We recommend that conservation efforts should avoid high intensity grazing (equivalent to > 1.3 kangaroos/ha), yet ensure enough grazing disturbance is maintained to promote the formation of complex grass structures. We also recommend that small floristically degraded and fragmented grassland habitat should be included in conservation efforts. These recommendations will likely benefit a number of faunal species in grasslands grazed by domestic and native grazers. Importantly, our data highlight the need for managing grazing regimes, even in environments dominated by native herbivores.     

Exclusion of livestock grazing and wood collection in dryland savannah: an effect on long‐term vegetation succession

Sahelian savannah faces increasing pressure from human activities, leading to its degradation. The aim of this study was to investigate the possibility of restoration of dryland savannah vegetation by the elimination of disturbance factors on the ecosystem. Is degraded dryland savannah vegetation able to be restored by means of natural succession? What is the timescale for its recovery? The study took place in the Bandia Reserve, 65 km south‐east of Dakar (Senegal), a unique site with two successional stages due to the elimination of uncontrolled exploitation. The vegetation structure of 15 years (15YRS) and 5 years (5YRS) after fencing was compared with vegetation exposed to continuous livestock grazing and wood collection outside the fenced area. Calculated by redundancy analysis, a significant effect of selected areas on the cover of all species was revealed and successional stage explained more than 45% of data variability. Perennial forbs, annual forbs and perennial grasses achieved the highest cover in 5YRS, woody species in 15YRS and annual grasses in the area outside of the fenced reserve. The dominant woody species Acacia seyal, A. ataxacantha, A. nilotica subsp. adstringens and Balanites aegyptiaca reconstituted the dense formation of Acacia bushland by means of natural succession in the 15YRS area.