Tree size and herbivory determine below-canopy grass quality and species composition in savannahs

Large single-standing trees are rapidly declining in savannahs, ecosystems supporting a high diversity of large herbivorous mammals. Savannah trees are important as they support both a unique flora and fauna. The herbaceous layer in particular responds to the structural and functional properties of a tree. As shrubland expands stem thickening occurs and large trees are replaced by smaller trees. Here we examine whether small trees are as effective in providing advantages for grasses growing beneath their crowns as large trees are. The role of herbivory in this positive tree-grass interaction is also investigated. We assessed soil and grass nutrient content, structural properties, and herbaceous species composition beneath trees of three size classes and under two grazing regimes in a South African savannah. We found that grass leaf content (N and P) beneath the crowns of particularly large (ca. 3. 5 m) and very large trees (ca. 9 m) was as much as 40% greater than the same grass species not growing under a tree canopy, whereas nutrient contents of grasses did not differ beneath small trees

Wild Ungulate Distribution in the Naban River Watershed National Nature Reserve, Southwest China

Southeast Asia´s tropical forests harbour a unique diversity of wildlife but species and numbers are rapidly declining under current land use. To improve conservation strategies in these biodiversity hotspots, knowledge of animal species present and their distribution is crucial. We wanted to identify the ungulate community composition and distribution of a ‘Man and Biosphere’ reserve, the Naban River Watershed National Nature Reserve (NRWNNR), Yunnan, Southwest China. Using camera traps, transects, and spoor-plots we identified wild ungulate species and corresponding habitat properties. We compared two study sites of different protection status – the buffer and experimental zones – on an overall transect length of 32 km and analysed relationships between wildlife activity, forest vegetation structure, and human disturbance. We documented six ungulate species, all of which occurred in the buffer zone while only three species were found in the experimental zone. Wild boar sign density was about 10 times higher in the buffer than in the experimental zone. Overall wildlife sign density increased with distance away from human settlements and closer to the core zone. Hence, human disturbance strongly influenced wild ungulate abundance but the NRWNNR was found to host a diverse ungulate community, considering its small size and compared to other conservation areas in the region. The combination of various methods proved to be successful in identifying and locating forest wildlife. The NRWNNR, particularly the more strongly protected zones, could greatly contribute to future ecotourism activities in Yunnan if a strict preservation of buffer and core zones can be maintained

Are Asian elephants afraid of honeybees? Experimental studies in northern Thailand

This research article published Springer Nature Switzerland AG., 2020In many parts of South and Southeast Asia, rural farmers living at the borders of protected areas frequently encounter Asian elephants (Elephas maximus) raiding their crops and threatening farmers lives and livelihoods. Traditional deterrent methods often have limited success as elephants become habituated or alternate their movement and behavior. While African bees (Apis mellifera scutellate) have been shown to effectively and sustainably deter African elephants (Loxodonta africana) little is known about their Asian counterparts. We conducted two experiments to estimate the effectiveness of bees as an Asian elephant deterrent method. We analyzed the behavioral reaction of seven captive Asian elephants when confronted with a fence of A. mellifera hives blocking their way to a desired source of food. In addition, we explored the defensive reaction of five A. cerana hives and six A. mellifera hives to an artificial disturbance during both day and night time. The elephants crossed the beehive fence in 51% of the cases, the probability of crossing increased over time and the number of exposures had a significant effect on an elephant’s crossing probability, indicating that elephants became habituated to the presence of the beehive fence. In the bee experiment, only one out of five A. cerana hives and one out of six A. mellifera hives reacted to the disturbance during the daytime, while during nighttime, none of them reacted defensively after being disturbed. We, therefore, conclude that neither A. mellifera nor A. cerana bees are likely to be effective in deterring wild Asian elephants from entering crop fields

Herbaceous forage and selection patterns by ungulates across varying herbivore assemblages in a South African savanna

Herbivores generally have strong structural and compositional effects on vegetation, which in turn determines the plant forage species available. We investigated how selected large mammalian herbivore assemblages use and alter herbaceous vegetation structure and composition in a southern African savanna in and adjacent to the Kruger National Park, South Africa. We compared mixed and mono-specific herbivore assemblages of varying density and investigated similarities in vegetation patterns under wildlife and livestock herbivory. Grass species composition differed significantly, standing biomass and grass height were almost twice as high at sites of low density compared to high density mixed wildlife species. Selection of various grass species by herbivores was positively correlated with greenness, nutrient content and palatability. Nutrient-rich Urochloa mosambicensis Hack. and Panicum maximum Jacq. grasses were preferred forage species, which significantly differed in abundance across sites of varying grazing pressure. Green grasses growing beneath trees were grazed more frequently than dry grasses growing in the open. Our results indicate that grazing herbivores appear to base their grass species preferences on nutrient content cues and that a characteristic grass species abundance and herb layer structure can be matched with mammalian herbivory types

A meta-analysis of the effects of communal livestock grazing on vegetation and soils in sub-Saharan Africa

Extensive livestock grazing is one of the most common and widespread forms of land uses in sub Saharan Africa (SSA). Studies assessing the effects of extensive livestock grazing on vegetation and soils in SSA are inconsistent in the direction and magnitude of study outcomes. We applied meta-analysis to identify whether studies so far conducted in the rangeland systems of SSA have detected significant rangeland degradation as approximated by changes in vegetation attributes (reduction in species diversity and richness; decreased biomass and ground cover; increased woody species density and canopy cover) and soil properties (Decreased soil OC, N and P). We quantified results of the included studies using the response ratio, which is the log proportional change in the means of a treatment and a control group. Four moderator variables (elevation (<1500 and ≥1500 m above sea level); plant life form (herbaceous and woody), rainfall amount (<600 mm and ≥600 mm), rainfall modality (mono and bimodal), and soil texture (Loam, sandy, sandy loam)) appeared to affect the response of species diversity and richness patterns to different grazing regimes, i.e., communal grazing systems, exclosures, livestock ranches and game reserves. Species diversity and richness values were generally lower in the communal grazing systems compared to the other grazing regimes. Only three moderator variables (rainfall amount and modality, and soil texture) affected the herbaceous basal cover response. Differences in soil OC were highest between communal and exclosure areas, visible at high elevations and under high rainfall. Soil N was influenced by rainfall modality and soil texture. We conclude that the effects of grazing regimes onto the environment cannot be generalized but are specific across vegetation and soil variables and differ considerably with rainfall and elevation

Modelling ungulate dependence on higher quality forage under large trees in African savannahs

In African savannahs, large trees improve grass quality, particularly in dry and nutrient poor areas. Enhanced below-canopy grass nutrients, such as nitrogen and phosphorus contents should therefore attract and benefit grazers. To predict whether ungulates really need these forage quality islands we focused on four grazer species, i.e., zebra, buffalo, wildebeest, and warthog, differing in body size and digestive system. We confronted literature estimations of their feeding requirements with forage availability and quality, observed in three South African savannah systems, through linear modelling. The model predicted the proportion of below-canopy grass that grazers should include in their diet to meet their nutritional requirements. During the wet season, the model predicted that all animals could satisfy their daily nutrient requirements when feeding on a combination of below- and outside-canopy grasses. However, wildebeest, having relatively high nutrient demands, could meet their nutrient requirements only by feeding almost exclusively below canopies. During the dry season, all animals could gain almost twice as much digestible protein when feeding on below - compared to outside-canopy forage. Nonetheless, only warthogs could satisfy their nutrient requirements - when feeding almost exclusively on below-canopy grasses. The other ungulate species could not meet their phosphorus demands by feeding at either site without exceeding their maximum fibre intake, indicating the unfavourable conditions during the dry season. We conclude that grazing ungulates, particularly warthog, zebra, and buffalo, actually depend on the available below-canopy grass resources. Our model therefore helps to quantify the importance of higher quality forage patches beneath savannah trees. The composition of grazer communities depending on below-canopy grasses can be anticipated if grazer food requirements and the abundance of large trees in savannahs are known. The model suggests that the conservation of large single-standing trees in savannahs is crucial for maintenance of locally grazing herbivore

Shifts in native ungulate communities on a former cattle ranch in Tanzania

When an area is brought under protection, current animal populations and their habitat preferences need to be assessed to predict population trends and future habitat availability. Using data from walking transects, we estimated the size of native ungulate populations on an abandoned cattle ranch in a coastal savannah in Tanzania, now included in the new Saadani National Park. Data were analysed with distance sampling and conventional strip transect techniques and were compared with results of previous wildlife counts. Few individuals of mainly browsing species were present in former cattle grazing areas exhibiting high bush-encroachment while a ten times higher biomass of browsers and grazers was found in the cattle-unmodified savannah. Population sizes of some species increased twofold between 1991 and 2001 within the entire area but neither population size nor species richness increased in the abandoned rangeland during our 3-year study period from 2001 to 2003. We conclude that the former ranch has potential for future recolonization by wild ungulates. Resettlement will take place gradually with 'pioneer-species' facilitating the entry of more demanding species. Habitat restoration through wildlife can be observed and quantified on Mkwaja Ranch which will be of importance for future management of native ungulates reclaiming abandoned rangeland

Enhanced use of beneath-canopy vegetation by grazing ungulates in African savannahs

The cover of large trees in African savannahs is rapidly declining, mainly due to human land-use practices. Trees improve grass nutrient quality and contribute to species and structural diversity of savannah vegetation. However, the response of herbivores to trees as habitat features is unknown. We quantified the habitat use of wild and domestic ungulates in two eastern and southern African savannahs. We assessed grazing intensities and quantified dung depositions beneath and around canopies of different sized trees. Grasses were eaten and dung was deposited twice as frequently beneath large (ca. 5 m in height) and very large trees (7-10 m) than in open grasslands. Small trees

Diet of the common warthog (Phacochoerus africanus) on former cattle grounds in a Tanzanian savanna

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. delta N-15 values of soil and plants also were highest in bomas and decreased significantly with distance, and high delta N-15 values in feces suggest that warthogs preferentially fed in the vicinity of the former bomas. delta C-13 values of warthog feces indicate that warthogs ingested on average 83% (77-98%) C-4 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