Plant functional traits are key to predict community responses to abiotic and biotic disturbances. Grazing is the dominant land‐use form in drylands and alpine environments, especially in Central Asian rangelands. Here, we address grazing effects and their relative importance against environmental controls on plant traits. We sampled 14 plant functional traits, which are potentially sensitive to grazing, from 127 taxa distributed across three grassland types in Tibetan grasslands exposed to increasing levels of precipitation: steppe, steppe‐meadow and meadow. We performed principal components analysis and fourth‐corner analysis to explore the impacts of grazing and environment on multiple community‐weighted mean (CWM) traits. We also used generaliszed linear mixed models to test the effects of grazing and environment on each CWM trait, and on three dimensions of functional trait diversity, i.e. functional richness (FRic), evenness (FEve) and divergence (FDiv). In addition, we undertook a mini‐review of former studies on grazing effects on plant traits in Chinese grasslands. We found that CWM traits were mainly affected by climate and elevation rather than by grazing intensity. Only plant tissue C content was negatively affected by intensified grazing across grassland types. Plant growth form and life form were mainly influenced by elevation, while heights of canopy and inflorescence were controlled by temperature. Specific leaf area was positively correlated with precipitation and soil total N content in steppes, while plant tissue N content was only correlated to livestock dung cover. Regarding functional trait diversity, FDiv in steppe‐meadows and meadows, and FEve in meadows were reduced by grazing. Synthesis. Our results confirmed that environmental controls override grazing impact on CWM traits across Tibetan alpine grasslands. Most plants and their respective traits are adaptive to alpine climates as well as to grazing, and are thus hardly affected by locally intensified grazing intensity. In steppes, functional diversity is insensitive to grazing due to the combined stress of drought and grazing. However, in steppe‐meadows and meadows, grazing may affect ecosystem functioning, as shown by the reduced values of FDiv and FEve under more intense grazing. A free Plain Language Summary can be found within the Supporting Information of this article.

Comparing genetic diversity, genetic differentiation, and performance between native and nonnative populations has advanced our knowledge of contemporary evolution and its ecological consequences. However, such between‐range comparisons can be complicated by high among‐population variation within native and nonnative ranges. For example, native vs. nonnative comparisons between small and non‐representative subsets of populations for species with very large distributions have the potential to mislead because they may not sufficiently account for within‐range adaptation to climatic conditions, and demographic history that may lead to non‐adaptive evolution. We used the cosmopolitan weed Conyza canadensis to study the interplay of adaptive and demographic processes across, to our knowledge, the broadest climatic gradient yet investigated in this context. To examine the distribution of genetic diversity, we genotyped 26 native and 26 nonnative populations at 12 microsatellite loci. Furthermore, we recorded performance traits for 12 native and 13 nonnative populations in the field and in the common garden. To analyze how performance was related to range and/or climate, we fit pedigree mixed‐effects models. These models weighed the population random effect for co‐ancestry to account for the influence of demographic history on phenotypic among‐population differentiation. Genetic diversity was very low, selfing rates were very high, and both were comparable between native and nonnative ranges. Nonnative populations out‐performed native populations in the field. However, our most salient result was that both neutral genetic differentiation and common garden performance were far more correlated with the climatic conditions from which populations originated than native vs. nonnative range affiliation. Including co‐ancestry of our populations in our models greatly increased explained variance and our ability to detect significant main effects for among‐population variation in performance. High propagule pressure and high selfing rates, in concert with the ability to adapt rapidly to climatic gradients, may have facilitated the global success of this weed. Neither native nor nonnative populations were homogeneous groups but responded comparably to similar environments in each range. We suggest that studies of contemporary evolution should consider widely distributed and genotyped populations to disentangle native vs. nonnative range effects from varying adaptive processes within ranges and from potentially confounding effects of demographic history.

No abstract

The Mongolian steppes with a long history of nomadic pastoralism cover a large area of the Palaearctic steppe biome and are still relatively intact. As livestock number has increased over the last two decades, grazing has been considered as the main reason of pasture degradation. However, the impact of grazing on vegetation dynamics, and its interaction with climate, is still not clear. We reviewed 44 publications in Mongolian language, covering 109 sites in five main steppe types, i.e., desert, dry, meadow, mountain, and high mountain steppe, with a mean annual precipitation and temperature range from 120 to 370 mm and from −6 to +5°C, respectively. We calculated relative changes in vegetation cover, species richness, and aboveground biomass from heavily grazed with respect to lightly/non-grazed conditions. Multiple linear regression models were used to test the impact of environmental factors, i.e., mean annual precipitation, coefficient of variation for precipitation, mean annual temperature and elevation. Grazing had a stronger effect on the vegetation of dry, desert and high mountain steppes, whereas its effect was less pronounced in the meadow and mountain steppes with mesic climate and high productivity. Vegetation cover, species richness and aboveground biomass were reduced by heavy grazing in the dry, desert and high mountain steppes. In the meadow steppes, grazing reduced vegetation cover, but increased richness and had nearly no effect on biomass. In the mountain steppe, richness and cover were not affected, but biomass was reduced by heavy grazing. Additionally, grazing effects on biomass tended to be more pronounced at sites with higher amounts of annual precipitation, and effects on cover changed from negative to positive as elevation increased. In conclusion, grazing effects in Mongolian steppes are overall negative in desert, dry and high mountain steppes, but no or even positive effects are found in meadow and mountain steppes. Especially, heavy grazing showed a detrimental effect on all vegetation variables in desert steppes, indicating the existence of combined pressure of climate and grazing in arid habitats, making them potentially sensitive to overgrazing and climate change. Grassland conservation and management should consider characteristics of different steppe types and give importance to local environmental conditions.

No abstract