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Disturbances from rodent engineering and human activities profoundly impact ecosystem structure and functioning. Whilst we know that disturbances modulate plant communities, comprehending the mechanisms through which rodent and human disturbances influence the functional trait diversity and trait composition of plant communities is important to allow projecting future changes and to enable informed decisions in response to changing intensity of the disturbances. Here, we evaluated the changes in functional trait diversity and composition of Afroalpine plant communities in the Bale Mountains of Ethiopia along gradients of engineering disturbances of a subterranean endemic rodent, the giant root-rat (Tachyoryctes macrocephalus Rüppell 1842) and human activities (settlement establishment and livestock grazing). We conducted RLQ (co-inertia analysis) and fourth-corner analyses to test for trait-disturbance (rodent engineering/human activities) covariation. Overall, our results show an increase in plant functional trait diversity with increasing root-rat engineering and increasing human activities. We found disturbance specific association with traits. Specifically, we found strong positive association of larger seed mass with increasing root-rat fresh burrow density, rhizomatous vegetative propagation negatively associated with increasing root-rat old burrow, and stolonifereous vegetative propagation positively associated with presence of root-rat mima mound. Moreover, both leaf size and leaf nitrogen content were positively associated with livestock dung abundance but negatively with distance from settlement. Overall, our results suggest that disturbances by rodents filter plant traits related to survival and reproduction strategies, whereas human activities such as livestock grazing act as filters for traits related to leaf economics spectrum along acquisitive resource-use strategy. [ABSTRACT FROM AUTHOR]

• Vegetation cover negatively affects activity of the ecological engineer root-rat. • Reciprocally, plant species richness positively affects activity of the giant root-rat. • Livestock grazing modulates the ecological engineering role of the giant root-rat. Subterranean rodents can act as ecosystem engineers by shaping the landscape due to soil perturbation and herbivory. At the same time, their burrow density is affected by environmental conditions, vegetation and anthropogenic factors. Disentangling this complex interplay between subterranean rodents and their environment remains challenging. In our study, we analysed the interplay of abiotic conditions, vegetation patterns and human land-use and the burrow density of the giant root-rat (GRR; Tachyoryctes macrocephalus), a subterranean rodent endemic to the Afroalpine ecosystem of the Bale Mountains in south-east Ethiopia. Specifically, we examined the effects of GRR on plant species richness and vegetation cover and vice-versa , and how these reciprocal effects might be modulated by temperature, habitat wetness and grazing. Our results showed that increasing GRR burrow density led to decreased vegetation cover, and that effects of GRR on vegetation cover were slightly stronger than vice - versa. Considering the reciprocal causation models, we found that increasing plant species richness led to increased GRR burrow density, while GRR burrow density decreased as vegetation cover increased. Increases in habitat wetness and livestock grazing intensity also directly led to increased GRR burrow density. Our results stress the importance of subterranean ecosystem engineers on vegetation and highlight the vulnerability of these complex interactions to human activity. [ABSTRACT FROM AUTHOR]

Understanding the interaction between large herbivores and pasture production, especially with respect to the grazing optimization hypothesis, is critical for pasture management and generating theoretical and testable predictions. However, the optimization hypothesis remains contradictory in alpine meadows on the Qinghai-Tibet Plateau (QTP). In this study, we tested the grazing optimization hypothesis using four yak-grazing intensities (no grazing, light grazing, moderate grazing and heavy grazing) in alpine meadow habitats from 2015 to 2017. The results indicated that species diversity did not differ significantly among grazing regimes during the experimental period. However, the aboveground net primary production (ANPP) under moderate grazing consistently significantly exceeded that in control enclosures over 3 years, confirming the grazing optimization hypothesis. Levels of overcompensation varied among grazing intensities and years, and grazing-induced plant compensation may only occur in the short term. The enhanced regrowth of Poaceae and Cyperaceae induced by yak grazing might contribute to the overall level of overcompensation by plant community. Our results strongly support the grazing optimization hypothesis in the context of alpine meadows grazed by yaks, emphasizing the complex interactions between ANPP, herbivores and other ecological factors in alpine meadows on the QTP. These findings provide new insights for the development of an ecological conservation strategy that will help restore this fragile ecosystem and balance the seemingly incompatible requirements of animal husbandry. [ABSTRACT FROM AUTHOR]

Aims The sedge Kobresia pygmaea is the dominant species of high-altitude pastures in Tibet, and it is the most important source of forage in animal husbandry. We present the first comprehensive reproduction study for this perennial key species that adopts a molecular approach and tests how sexual and vegetative reproduction, as well as ploidy, relate to survival and dominance under harsh conditions. Methods We assessed inflorescence numbers of K. pygmaea across two Tibetan alpine pastures with differing grazing regimes. Germination was tested in untreated diaspores and then following mechanical and chemical scarification. In a 4-year experiment, we assessed diaspore viability and seed bank formation. Using eight microsatellite markers, we recorded multilocus genotypes in hierarchical grids and measured their ploidy using flow cytometry. Adjusted analysis of variance models were used to analyse data on sexual reproduction, while the complement of the Simpson index and the Shannon diversity index were used to characterize the spatial distribution of multilocus genotypes and clonal richness. Important Findings Inflorescence production was high and differed significantly between years (2010: 617 ± 460 SD; 2012: 2015 ± 1213 SD) but not between grazing regimes. Diaspore viability was high (94%) and gradually decreased after 3 and 4 years of storage in the soil. Diaspores not exposed to further scarification failed to germinate, while mechanical and chemical (H2SO4) scarification increased germination to 9 and 44%, respectively. Clonal diversity was high, although in situ germination was rarely observed. Multilocus genotypes intersected and covered a mean area of 0.74 m². Most individuals were found to be tetraploid, with only 0.8% of all ramets being triploid. We conclude that K. pygmaea survives on the Tibetan Plateau by employing a mixed reproduction strategy involving both sexual and clonal propagation. The species' adaptability and dominance is further facilitated by its polyploidy. As pasture restoration using diaspores would be difficult, existing Kobresia pasture should be managed more sustainably. [ABSTRACT FROM AUTHOR]

Abstract: The age at which a human environment was made is strongly debated in Quaternary science. The perception of the human footprint requires an understanding of the contrast between the present cultural environment and the natural vegetation. This is especially true for high altitude ecosystems, such as the world's largest alpine ecosystem, the 450,000 km2 of golf-course-like pastures dominating the southeastern Tibetan Plateau. This ecosystem is widely considered to be natural, but only because of the unawareness of the effects of grazing management and the incorrect assessment of human signals in palaeo proxies. Here we posit the hypothesis that this ecosystem is a human-induced replacement. To test our hypothesis against defined a priori criteria, we 1) monitored vegetation in grazing exclosures; 2) produced floristically complete vegetation records; 3) compared the vegetation records with data of the nearest climate stations; 4) surveyed forest and experimental reforestation trials with endemic tree species; 5) analyzed pollen and re-evaluated published pollen diagrams; and 6) integrated these results with palaeopedological and anthracological results of previous studies. The results of long-term grazing exclosure experiments, the prevalence of grazing-adapted plant functional types, the occurrence of isolated vigorous forests in “alpine” pastures, and the successful reforestation trials in presently treeless pastures together suggest that dominant pastures replaced forests in the montane belt and tall grassland in the alpine belt. The spatial and temporal coincidence of palaeosols and archaeological sites with tree species charcoal, the decline in forest pollen during the mid-Holocene climatic optimum, and the first appearance of human indicator pollen are most parsimoniously explained by the early presence of foragers and pastoralists. The onset of pastoralism in the Tibetan Highlands is presumed to date from the 8th millennium BP. [Copyright &y& Elsevier]

Since the late 1950s, governmental rangeland policies have changed the grazing management on the Tibetan Plateau ( TP). Increasing grazing pressure and, since the 1980s, the privatization and fencing of pastures near villages has led to land degradation, whereas remote pastures have recovered from stronger overgrazing. To clarify the effect of moderate grazing on the carbon ( C) cycle of the TP, we investigated differences in below-ground C stocks and C allocation using in situ 13 CO2 pulse labeling of (i) a montane K obresia winter pasture of yaks, with moderate grazing regime and (ii) a 7-year-old grazing exclosure plot, both in 3440 m asl. Twenty-seven days after the labeling, 13 C incorporated into shoots did not differ between the grazed (43% of recovered 13 C) and ungrazed (38%) plots. In the grazed plots, however, less C was lost by shoot respiration (17% vs. 42%), and more was translocated below-ground (40% vs. 20%). Within the below-ground pools, <2% of 13 C was incorporated into living root tissue of both land use types. In the grazed plots about twice the amount of 13 C remained in soil (18%) and was mineralized to CO2 (20%) as compared to the ungrazed plots (soil 10%; CO2 9%). Despite the higher contribution of root-derived C to CO2 efflux, total CO2 efflux did not differ between the two land use types. C stocks in the soil layers 0-5 and 5-15 cm under grazed grassland were significantly larger than in the ungrazed grassland. However, C stocks below 15 cm were not affected after 7 years without grazing. We conclude that the larger below-ground C allocation of plants, the larger amount of recently assimilated C remaining in the soil, and less soil organic matter-derived CO2 efflux create a positive effect of moderate grazing on soil C input and C sequestration. [ABSTRACT FROM AUTHOR]

Abstract: Arid and Alpine ecosystems are known for extreme environmental changes during the Late Quaternary. We hypothesize that the world''s largest Alpine arid ecosystem however, the Alpine Steppes of the Tibetan highlands, remained ecologically stable during the LGM and the mid-Holocene. This hypothesis is tested by distributional range of plant species, plant life forms and rate of endemism. The set of character species has a precipitation gradient between 50 and 350mm/a, testifying for resilience to precipitation changes. 83% of the species have a wider vertical range than 1000m used as a proxy for resilience to temperature changes. 30% of the species are endemic with 10 endemic genera, including plate-shaped cushions as a unique plant life form. These findings are in line with palaeo-ecological proxies (δ18O, pollen) allowing the assumption that Alpine Steppes persisted during the LGM with 3 to 4K lower summer temperatures. During the mid-Holocene, forests could have replaced Alpine Steppes in the upper catchments of the Huang He, Yangtze, Mekong, Salween and Yarlung Zhangbo, but not in the interior basins of the north-western highlands, because the basins were then flooded, suppressing forests and supporting the environmental stability of this arid Alpine grassland biome. [Copyright &y& Elsevier]

Abstract: The Tibetan highlands host one of the world''s largest pastoral ecosystems, but the evolutionary impact of the Tibetan nomadic livestock economy on the environment has not yet been investigated. Despite this grazing impact, the vegetation of the Tibetan highlands is widely believed to be natural. Our ecological approach to reconstructing the making of a pastoral environment uses the present composition of the plant cover as a baseline. Today''s prevailing plant functional types are grazing weeds highly adapted to grazing. The first pollen record of grazing weeds can thus be assumed to mark the onset of pastoralism, supposedly with goats and sheep introduced from the Middle East and the endemic large bovid of the yak, domesticated in the Tibetan highlands. This study represents the first attempt to determine the age of pastoralism with the help of palynomorphs using the indicator-species approach. This is independently corroborated 1) by the synchronous occurrence of pollen clumps indicating disturbance effects from trampling and 2) the precipitous decline of forest pollen on the eastern declivity of the highland during the mid-Holocene climatic optimum. As all pollen core sites currently have a climatic potential of forest as demonstrated by fruiting and progenitive forest relicts, it is suggested that early livestock holders continued to burn these forests to obtain pastures. The charcoal record supports this conclusion. It is hypothesized that the making of a pastoral environment in the Tibetan highlands started around 8.8 ka cal BP during the mid-Holocene climatic optimum. As the pattern of arboreal pollen decline at these sites contrasts with δ 13C, δ 18O, TOC content, C/N ratio, and ostracod assemblages that are independent of rangeland management decisions of early pastoralists, we may conclude that pastoralists took advantage of the mid-Holocene climatic optimum to convert forests into high-yield pastures. Using pollen clumps as a proxy for herbivore load suggests a tenfold higher amount of livestock than of wildlife before the introduction of pastoralism. In contrast to pastoralism in arid environments of the Old World''s desert belt, pastoralists in the eastern Tibetan highlands created their own environment transforming forests and tall grassland into the present golf course-like pastures. [Copyright &y& Elsevier]

The lithology, ostracods, palynomorphs and black carbon of a sediment core from a saline wetland in the southern Tibetan highlands (29°14′33.40″N/87°13′09.10″E, 4480 m a.s.l., A.R. Xizang, China) is analyzed and climate modelling applied with respect to core questions in Quaternary research: (1) Do meso-climatic effects of regional landscape structures like high mountains overrule the effects of global climates? (2) Did life persist during the LGM? (3) Which shifts in ecosystems can be detected? (4) Does the fire-record testify for the presence of humans and their environmental impact? (5) How old is Neolithisation in the world's largest highlands? The results of this integrated multi-disciplinary investigation revealed (1) the meso-climatic effect of the Himalayan arc's relief channeled westerlies with West-Himalayan forest-pollen types into the southern Tibetan highlands, with (2) higher winter-precipitation, slightly lower summer precipitation, and the persistence of life for plants, and herbivores and therefore probably hunters. (3) The most arid period occurred between 17.8 and 15 cal kyr B.P., possibly synchronous with the Heinrich 1 event. Around 14.8 cal kyr B.P. humidity increased with torrential rains of high erosive power on sparsely plant-covered slopes and lasted until 4 cal kyr B.P. (4) The continuous fire-record proved the availability of combustible matter and a constant fire source which is believed to be human-attributed. Charcoal peaks around 17, 16 and 13 cal kyr B.P. remained sporadic until 11.5 cal kyr B.P. and attained the highest values since 8.7 cal kyr B.P. Black carbon increased steadily until 11 cal kyr B.P. and sharply peaked with high fluctuations around 10 cal kyr B.P., indicating high frequency intensive fires at the beginning of the Holocene. Between 10 and 6 cal kyr B.P. fire frequency decreases, with a slight peak around 4 cal kyr B.P. (5) The dawn of pastoralism in the early Mid Holocene Climatic Optimum dated back to 8.7 cal kyr B.P. with a decline of grass-pollen and the synchronous emergence of grazing weeds, leaving a perception gap of 5000 years between the palaeo-ecological and the archaeological state of the art. • Persistence of life during late LGM with higher snowfall and lower summer-rainfall. • Westerlies are channeled along the Himalayas into south Tibet during weak monsoon. • Charcoal and black carbon testify for the fire impact during the last 17,000 years. • Grazing indicator pollen show the onset of herding before 8700 years. • Data gap between archaeology and palynology of 5000 years about the Neolithisation. [ABSTRACT FROM AUTHOR]

Understanding the impacts of livestock grazing is crucial to rangeland management and conservation. Numerous indicators have been employed to detect differences caused by grazing, while case studies suggest that effects differ among individual indicator systems. Across Tibetan pastures that have evolved with long grazing histories and harbour high levels of biodiversity, we tested: (1) whether commonly used grazing indicators differ in their sensitivity to grazing and environmental conditions, and (2) the relative importance of grazing and abiotic factors in controlling effects on indicators. Our sampling covered 18 sites within two main grassland types (steppe and meadow). We compared species compositions among communities of plants, small mammals and ants, as well as overall soil chemical conditions and field hyperspectral reflectance data using multivariate analyses between two qualitative levels of grazing intensity (heavy vs. light). Using univariate Generalized Linear Models, we explored the effects of grazing intensity, grassland type and their interaction on the richness and abundance of biotic groups as well as values of key soil and hyperspectral indices. The major environmental factors tested included temperature, precipitation, elevation, relief, exposure and inclination. Few of the indicators differed under relatively heavy grazing, including reductions in vegetation cover, soil organic carbon, total nitrogen concentration and two hyperspectral indices. Indicator groups differed both quantitatively and qualitatively with respect to grazing and climate impacts. Grazing effects were evident in the moist Kobresia meadows of eastern Tibet, while environmental controls dominated in alpine steppes of the drier western part of the plateau. Grazing effects on indicators thus depended on local precipitation conditions. Multivariate species compositions were affected by abiotic factors in all biotic indicator groups: precipitation was the most influential abiotic factor affecting plant species composition, overall soil nutrients and hyperspectral data, while elevation and temperature influenced ant and small mammal communities in terms of richness and species composition. Our results do not support the notion that local increases in relative grazing intensity have strong effects on the species richness of key biotic indicator groups across all Tibetan pastures. Reliable assessments of grazing effects thus require both multiple appropriate indicators and careful calibration to account for local climate and topographic conditions. Differences between principal grassland types must be acknowledged for future grassland conservation and management. [ABSTRACT FROM AUTHOR]

The Tibetan highlands host the largest alpine grassland ecosystems worldwide, bearing soils that store substantial stocks of carbon (C) that are very sensitive to land use changes. This study focuses on the cycling of photoassimilated C within a Kobresia pygmaea pasture, the dominating ecosystems on the Tibetan highlands. We investigated short-term effects of grazing cessation and the role of the characteristic Kobresia root turf on C fluxes and belowground C turnover. By combining eddy-covariance measurements with 13 CO 2 pulse labeling we applied a powerful new approach to measure absolute fluxes of assimilates within and between various pools of the plant-soil-atmosphere system. The roots and soil each store roughly 50% of the overall C in the system (76 Mg C ha − 1 ), with only a minor contribution from shoots, which is also expressed in the root:shoot ratio of 90. During June and July the pasture acted as a weak C sink with a strong uptake of approximately 2 g C m − 2 d − 1 in the first half of July. The root turf was the main compartment for the turnover of photoassimilates, with a subset of highly dynamic roots (mean residence time 20 days), and plays a key role for the C cycling and C storage in this ecosystem. The short-term grazing cessation only affected aboveground biomass but not ecosystem scale C exchange or assimilate allocation into roots and soil. [ABSTRACT FROM AUTHOR]