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

Marginalised herders: social dynamics and natural resource use in the fragile environment of the Richtersveld National Park, South Africa

This research article published by Elsevier B.V., 2018In the contractual Richtersveld National Park (RNP), park officials and neighbouring communities jointly manage resources, with the aim to harmonize biodiversity conservation and human land use. Our socio-ecological approach compared herding practices and livelihoods of 36 livestock owners and 35 hired herders inside and outside RNP, and further assessed soil quality and vegetation characteristics under different livestock grazing patterns and access to natural resources. Hired herders were mainly in charge of animal movement patterns but were not included in formal agreements, which negatively impacted on natural resource management, livelihoods, animal well-being and communication amongst stakeholders. Soil properties and vegetation were generally negatively affected through grazing and herding practices in this fragile semi-arid biodiversity hotspot that encompasses many endangered and endemic species. Our research highlights the complex social relationships and dynamics between diverse stakeholders engaged in the contractual park and accentuates the need to improve herders’ social and economic status

The importance of nutrient hotspots for grazing ungulates in a Miombo ecosystem, Tanzania

While movement patterns of grazing ungulates are strongly dependent on forage quality their use of nutrient hotspots such as termite mounds or grazing lawns has rarely been quantified, especially in savanna ecosystems where soil-nutrient quality is low. Additionally, few experiments have been conducted to determine the role of termite mound- and grazing lawn-derived soils in improving forage quality in the field. We studied wild ungulate grazing activities around ten termite mounds, six grazing lawns and their respective control sites in a Miombo system of Issa Valley, western Tanzania, in the same system. We used indirect observations (i.e., dung, tracks) to identify seasonal and spatial variations in habitat use of various wild mammalian grazers. Grazer visitation rates were nine and three times higher on termite mounds and grazing lawns, respectively, compared to control sites. During the rainy season, termite mounds were more frequently used than grazing lawns while the latter were used more often during the dry season. In an additional pot experiment with soils derived from different areas, we found that Cynodon dactylon in termite mound-derived soils had twice as high Nitrogen and Phosphorous contents and biomass compared to grasses planted in grazing lawn soils and control site soils. We highlight that both termite mounds and grazing lawns play a significant role in influencing seasonal nutrient dynamics, forage nutrient quality, habitat selectivity, and, hence, grazing activities and movement patterns of wild ungulate grazers in savannas. We conclude that termite mounds and grazing lawns are important for habitat heterogeneity in otherwise nutrient–poor savanna systems

Pre- and Post-Degradation Management of Rangelands: Implications for Sustainable Management

Rangeland degradation directly affects livestock production, resulting in food insecurity and ecological instability. A shift in vegetation from grass to woody plants has severely affected cattle production in Ethiopian rangelands. Those grass species that are perceived by the pastoralists as highly palatable and desirable are currently decreasing in both quality and quantity. A reason for this decline has been claimed to be degradation owing to overgrazing and climate change. While appropriate management of livestock density in rangelands is essential for sustainable production and grassland ecosystem health, the management of dryland ecosystems is mired in controversy due to the complexity of the ecosystem. This region is categorized as a non-equilibrium environment, though at times it experiences equilibrium characteristics, which makes the management of the Borana rangelands highly complex. A better understanding of grass productivity and its controlling factors in modern savanna ecosystems could be a key to understanding the productivity of savannas and to predict responses to future climatic changes. The development of effective management strategies for responding to climatic variability is often impeded by the lack of a systematic framework for analyzing livestock stocking policies and management practices. Further, effective decision making requires an understanding of the important biotic and abiotic components of rangeland systems, such as the response of rangeland vegetation to environmental stressors: climatic change and herbivorous population dynamics. Previous vegetation studies of the Borana rangelands focused mainly on taxonomic descriptions and rangeland condition assessments. Reseeding of degraded rangelands is a potential management option in eastern African rangelands to enhance the resilience of rangelands. Therefore, it is high time to understand how the native perennial grass individuals respond to increased herbivory under higher drought frequency after reseeding

Anthropogenic disturbance and chimpanzee (Pan troglodytes) habitat use in the Masito-Ugalla Ecosystem, Tanzania

The habitat quality of chimpanzee (Pan troglodytes), including the availability of plant food and nesting species, is important to ensure the long-term survival of this endangered species. Botanical composition of vegetation is spatially variable and depends on soil characteristics, weather, topography, and numerous other biotic and abiotic factors. There are few data regarding the availability of chimpanzee plant food and nesting species in the Masito-Ugalla Ecosystem (MUE), a vast area that lies outside national park boundaries in Tanzania, and how the availability of these resources varies with human disturbance. We hypothesized that chimpanzee plant food species richness, diversity, and abundance decline with increasing human disturbance. Further, we predicted that chimpanzee abundance and habitat use is influenced negatively by human disturbance. Published literature from Issa Valley, Gombe, and Mahale Mountains National Parks, in Tanzania, was used to document plant species consumed by chimpanzees, and quantify their richness, diversity, and abundance, along 32 transects totaling 63.8 km in length across four sites of varying human disturbance in MUE. We documented 102 chimpanzee plant food species and found a significant differences in their species richness (H = 55.09, P 0.964). The least disturbed site exhibited the highest encounter rate of chimpanzee nests/km, with rates declining toward the highly disturbed sites. Our results show that severe anthropogenic disturbance in MUE is associated with the loss of chimpanzee plant food species and negatively influences chimpanzee habitat use, a relationship that threatens the future of all chimpanzee populations outside national parks

Back to the Roots - Do Traditional Maasai Management Strategies Work towards Resilience against Unpredictable Rainfall and Grazing Pressure in Northern Tanzania?

Despite the importance for people´s livelihoods, many semi-arid African savannas are prone to heavy degradation due to overutilization by people, livestock and increased climate variability. Rangeland management, such as transhumance and deferred grazing systems, practiced by the Maasai in northern Tanzania, can be useful in combating the negative consequences of overuse and increasing rainfall variability. But little is known on how different rangeland regimes, practiced by the Maasai, impacts the productivity of these rangelands. We collected data on regrowth rates under different rangeland management regimes (rainy season grazing land, dry season grazing land, and seasonal exclosures), different harvest rates (month, season) and additional, uncontrolled grazing (fenced, open plots). We conducted the experiment for two consecutive growing seasons 2019 (GS1) and 2019/2020 (GS2). Grass regrowth rates were similar for all rangeland management regimes. During dry conditions in GS1 seasonally cut plots showed significantly higher grass regrowth compared to monthly cut plots, when fenced. Outside the fence grass regrowth was generally lower and similar for both harvest rates. During high rainfall conditions in GS2, seasonally cut plots showed higher grass regrowth independent of fencing. Regrowth rates of forbs were not impacted by any treatment during GS1. It increased by 5 times during GS2, and was significantly higher in the seasonally cut plots then. Our results suggest that recovery phases between heavy grazing events is crucial to maintain forage provision of the rangelands. Uncontrolled additional grazing can hamper the rangeland productivity during times of low rainfall, but seem not to have influence when rainfall is frequent. Traditional rangeland management is based on the concept of granting seasonal recovery periods, which seems to be an effective way to maintain rangeland productivity despite intense harvest and unpredictable rainfall pattern. Implementation and control of grazing plans are crucial, particularly during times of drought

A 3,500-year tree-ring record of annual precipitation on the northeastern Tibetan Plateau

An annually resolved and absolutely dated ring-width chronology spanning 4,500 y has been constructed using subfossil, archaeological, and living-tree juniper samples from the northeastern Tibetan Plateau. The chronology represents changing mean annual precipitation and is most reliable after 1500 B.C. Reconstructed precipitation for this period displays a trend toward more moist conditions: the last 10-, 25-, and 50-y periods all appear to be the wettest in at least three and a half millennia. Notable historical dry periods occurred in the 4th century BCE and in the second half of the 15th century CE. The driest individual year reconstructed (since 1500 B.C.) is 1048 B.C., whereas the wettest is 2010. Precipitation variability in this region appears not to be associated with inferred changes in Asian monsoon intensity during recent millennia. The chronology displays a statistical association with the multidecadal and longer-term variability of reconstructed mean Northern Hemisphere temperatures over the last two millennia. This suggests that any further large-scale warming might be associated with even greater moisture supply in this region

On the Move – Do Domestic and Wild Ungulate Species Distributions Overlap in the Mongolian Gobi?

In the Great Gobi B Strictly Protected Area (Great Gobi B), wild and domestic ungulates seasonally share the forage of the semi-desert and desert habitat. Around 130 herder families are grazing their livestock, mainly goats and sheep, in the protected area in winter. Wild ungulates of global significance in Great Gobi B include the reintroduced Przewalski’s horse (Equus ferus przewalskii),which had previously been extinct in the wild. To determine potential habitat overlaps between Przewalski’s horses and livestock, we mapped the movements of 19 livestock herds monitored via GPS collars and ranger observations of Przewalski’s horse herds over a one year period from September 2018 to August 2019. We additionally conducted focus group interviews with nomadic herders about their rangeland management. We found that pasture use in and around the Great Gobi B is still following the nomadic tradition, with herders moving camp locations on average eleven times per year, depending on forage availability. Our results show that the range of Przewalski’s horses and livestock mostly overlap around permanent and ephemeral water points. However, the same resources are used in different seasons. The protected area was recently expanded to twice its size, now also including additional herder households and traditional pastures. For the ongoing discussion about concerning the new zonation of the enlarged protected area it is important to consider both, herder and wildlife movements patterns, to meet the conservation goals of the protected area but also meet the needs of the traditional pastoral herding community

Uniform growth trends among central Asian low- and high-elevation juniper tree sites

We present an analysis of 28 juniper tree-ring sites sampled over the last decades by several research teams in the Tien Shan and Karakorum mountains of western central Asia. Ring-width chronologies were developed on a site-by-site basis, using a detrending technique designed to retain low-frequency climate variations. Site chronologies were grouped according to their distance from the upper timberline in the Tien Shan (∼3,400ma.s.l.) and Karakorum (∼4,000m), and low- and high-elevation composite chronologies combining data from both mountain systems developed. Comparison of these elevational subsets revealed significant coherence (r=0.72) over the 1438-1995 common period, which is inconsistent with the concept of differing environmental signals captured in tree-ring data along elevational gradients. It is hypothesized that the uniform growth behavior in central Asian juniper trees has been forced by solar radiation variations controlled via cloud cover changes, but verification of this assumption requires further fieldwork. The high-elevation composite chronology was further compared with existing temperature reconstructions from the Karakorum and Tien Shan, and long-term trend differences discussed. We concluded that the extent of warmth during medieval times cannot be precisely estimated based on ring-width data currently availabl