Grasslands are globally abundant and provide many ecosystem services, including carbon (C) storage. While grasslands are widely subject to livestock grazing, the influence of grazing on grassland ecosystem C remains unclear. We studied the effect of long-term livestock grazing on C densities of different ecosystem components in 110 northern temperate grasslands across a broad agroclimatic gradient in Alberta, Canada. These grasslands stored 50 to 180 t ha(-1)C in live and dead vegetation, as well as soil C to 30 cm depth, with the majority as soil organic C (SOC). The mulch layer comprised a large amount of C (similar to 18 t ha(-1)C) especially within humid grasslands. Although grazing reduced C densities in litter mass, total ecosystem C was 8.5 % greater under grazing (127.8 t ha(-1)) compared to those non-grazed (117.8 t ha(-1)), primarily due to increases in SOC and roots. Increases in SOC were consistently observed in the 0-15 cm layer across all climatic conditions, with changes in SOC of the 15-30 cm layer inversely related to aridity. A structural equation model revealed that increased SOC under grazing was indirectly attributed to increases in eudicot rather than graminoid biomass. In addition, SOC increased with graminoid quality (i.e., a reduced carbon to nitrogen ratio), which together with elevated eudicots, increased litter and mulch C, and ultimately enhanced SOC densities. When applied to spatial maps of habitat type and land use (livestock grazing) activity across the region, an area of similar to 3.8 M ha of grassland was projected to contain an additional 17.1 M t of C under grazing, primarily in mesic grasslands, worth an estimated $3.1 B (Cdn.) under current C valuation guidelines in Canada. Overall, these results highlight the importance of grasslands for C storage and establishing policies that maintain and promote their sustainable use, including light to moderate grazing.

Globally, grasslands, covering about 40% of the Earth's land area, are vital for supporting important ecosystem functions, services, and livelihoods of millions of humans. Currently, grassland degradation is a major threat to the maintenance of ecological services,1Bardgett R.D. Bullock J.M. Lavorel S. et al.Combatting global grassland degradation.Nat. Rev. Earth Environ. 2021; 2: 720-735Crossref Scopus (47) Google Scholar food security, and sustainable development, and directly hinders the global efforts with meeting goals and targets such as the The UN Decade on Ecosystem Restoration and Sustainable Development Goals (SDGs). Remote sensing approaches have the advantages of spanning large geographical areas with multiple spatial, spectral, and temporal resolutions. In global scale, remote sensing methods used normalized difference vegetation index to determine net primary productivity (NPP), which still is the effective method to indicate grassland conditions. To master the general situation of grassland, we analyzed the global spatial-temporal variation of NPP from 2001 to 2019 at the pixel level across the globe. As presented in Figure 1A, the NPP values of global grasslands showed an obvious variation trend, which indicated a considerable distribution pattern of spatial heterogeneity. The decreasing and increasing trend in grassland NPP covered approximately 25.3% and 74.5% of the total grassland area, respectively. We observed the highest proportion of degradation in Australia (45.5%). Conversely, 73.7% of the total grassland area revealed an increasing NPP trend, especially in Canada (86.4%). These changes are predicted to have huge effects on biodiversity and the livelihoods of approximately 1.5 billion people who rely on grassland ecosystem services and sustainability. In general, current grassland degradation research explicitly links climate change and human activities to landscape patterns, soil properties, community traits, and ecosystem functions. While previous studies provide a theoretical basis for grassland degradation,2Coban O. De Deyn G.B. van der P.M. Soil microbiota as game-changers in restoration of degraded lands.Science. 2022; 375: eabe0725Crossref Scopus (7) Google Scholar they use different definitions and classifications, which is a barrier to comprehensive global utilization. Our understanding of the concept of grassland degradation has evolved in the past 100 years (1919–present) through three stages: biotic/abiotic indicators, ecosystem functions, and ecosystem services (Figure 1B). Before the 1990s, soil organic carbon was used as an index, likely representing the first discussion about grassland degradation. In 1979, the Food and Agriculture Organization (FAO) defined grassland degradation as a "process which lowers the capability of soils to produce food and fodder.". Then, during the 1990s, grassland degradation is defined as the reduction in the capacity of grasslands to carry out their key ecosystem functions (Figure 1B). The United Nations (UN) Convention to Combat Desertification paid more attention to the loss of biological or economic productivity and diversity of grassland ecosystem. Since the 20th century, some researchers have begun to define grassland degradation as the long-term loss of ecosystem function and services caused by disturbances from which the system cannot completely recover, following which the FAO also clarified in 2014 degradation as a reduction in the ability of grassland to provide ecosystem goods and services (Figure 1B). To summarize, in the past century, scientists have accumulated a more concrete understanding of grassland degradation, from the change in visible indicators to the alteration of deep-seated social goods, functions, and services. Any definition of grassland degradation is essentially a grassland sustainability problem. Due to the inconsistent definition of grassland degradation, different assessment indicators emerged across various countries, bringing challenges to grassland sustainability research. To standardize the degradation measure and achieve large-scale evaluation, based on remote sensing methods, some assessments have used vegetation index or NPP, which could reflect grassland degradation through calculating the slope or index. However, due to the limitations of associations between satellites and unobservable variables (e.g., soil nutrient status), the use of remote sensing for the assessment of grassland degradation has been impeded. Therefore, others have opted to use the ecosystem function of carbon and nutrient cycling and the remote sensing of fractional surface cover to estimate degradation. In addition, field investigation is necessary to address issues related to grassland restoration and sustainability, soil/site stability, hydrologic function, and biotic integrity. Phyto-ecological indicators were used for the quantitative assessment of grassland degradation. Socioeconomic factors are emerging to be key; more surveys of changing rangelands areas, degradation index, and data gathered from ranchers and range management experts are leading to a qualitative change in grassland degradation assessment. The Visual Soil Assessment was developed in New Zealand to provide a simple method to assess soil and plant quality semi-quantitatively, quickly, and effectively. This method is based on a weighted additive model, which includes indicators of soil quality (both static and dynamic) and plant performance. Moreover, since 2008, this method has been recommended by the FAO to herdsmen and scientists for its simplicity. Accordingly, grassland degradation assessment has progressed from a single factor to multiple factors, and from large scale to pasture level, which all point to the evaluation of grassland sustainability. Obviously, limiting the grassland deterioration and achieving its sustainability requires all relevant stakeholders to work together to reach a consensus and consider all aspects for its key role in global climate change and human welfare.3Sun J. Fu B.J. Zhao W.W. et al.Optimizing grazing exclusion practices to achieve goal 15 of the sustainable development goals in the Tibetan plateau.Sci. Bull. 2021; 66: 1493-1496Crossref Scopus (19) Google Scholar To achieve sustainable development of the grassland ecosystem, there is a fundamental need to define and assess the extent of grassland degradation and unravel the causes and processes of grassland degradation. Accurately assessing grassland ecosystem sustainability will require us to understand the impact of grassland degradation in the social-ecological system. Here, we defined grassland sustainability as the resistance, resilience, and recovery of complex social-ecological-bioeconomic system, which involves the background of habitat, available resource, practical patterns, livestock production, and financial and political influence. Consequently, the essence of measuring grassland degradation is to evaluate whether the grassland ecosystem is sustainable. Nevertheless, the assessment of grassland degradation is a challenge because of the complexity of methods, criteria, habitats, management, tenure, policies, and culture. Therefore, developing a uniform conceptual model and methodology to assess grassland sustainability is of high importance. In our paper, we conceptualize a framework for grassland sustainability that is coupled with policymaker-performer-evaluator and evaluation system combined with ecosystem indicators, functions, services, and social systems, which ultimately attempts to achieve a grassland sustainability assessment (Figure 1B). To quantify grassland sustainability, we introduced the StageTHREE sustainable grasslands model,4Behrendt K. Liu H. Takahashi T. et al.StageTHREE Sustainable Grassland Model (v1.07): Model Description and Users Guide. Australian Centre for International Agricultural Research (ACIAR), 2020Google Scholar which developed as part of the Australian Centre for International Agricultural Research (ACIAR) project in 2020. Specifically, a grassland sustainability assessment should also consider the stakeholders, collaborations, and mutual relationships among different administrative departments (e.g., government, scientist, rancher). Through the understanding of the process and challenges of grassland degradation, we would be able to carry out grassland sustainability assessment. Grassland degradation is often accompanied by the change in basic indicators (e.g., coverage, water infiltration rate, plant biomass), which are components or measures of environmentally or ecologically relevant phenomena used to depict or evaluate environmental or ecological conditions. Through the observation of a series of key indicators, we can analyze different ecosystem functions of grassland such as carbon sequestration, nitrogen cycling, and microbial activity,2Coban O. De Deyn G.B. van der P.M. Soil microbiota as game-changers in restoration of degraded lands.Science. 2022; 375: eabe0725Crossref Scopus (7) Google Scholar which reflect the biotic and abiotic processes that may contribute to ecosystem services either directly or indirectly. Considering the benefits humans obtain from grassland ecosystems, the cultural, provisioning, regulating, and supporting ecosystem services are key to establishing ecological-social system relations, and assessing grassland sustainability from a human-nature relationship perspective.1Bardgett R.D. Bullock J.M. Lavorel S. et al.Combatting global grassland degradation.Nat. Rev. Earth Environ. 2021; 2: 720-735Crossref Scopus (47) Google Scholar Most important, in addition to the above assessment, determining the sustainability of grassland ecosystem must integrate various factors such as policy and market,5Behrendt K. Takahashi T. Kemp D.R. et al.Modelling Chinese grassland systems to improve herder livelihoods and grassland sustainability.Rangel. J. 2020; 42: 329-338Crossref Scopus (5) Google Scholar which influence how herdsmen make decisions about using and managing grasslands via household strategies and, more broadly, community institutions. Urgent action is needed to halt grassland degradation processes and to restore its sustainability, which requires the topic of grassland sustainability to be given a global priority that helps to alleviate poverty, and to increase carbon sink so as to attain zero net degraded land goal and SDGs. Therefore, authoritative, frequent assessments of type, standard definition, classification, trends, driving factors, and policy challenges of grassland degradation become crucial. Based on the above consensus, for the social attributes linked with livelihoods and poverty, a standardized methodology of grassland sustainability is needed rather than only grassland degradation. Considering effective assessment, such a methodology could effectively disseminate practical knowledge of restoration, and ensure that governments promote grassland sustainability for the benefit of their residents and all humankind. Therefore, building a grassland sustainability framework and action plan should be incorporated into the work of multilateral environmental agreements and organizations, such as the Convention on Biological Diversity, the UN Framework Convention on Climate Change, and the content of the UN's post-2015 development agenda oriented toward the achievement of the global SDGs. If the degraded grassland ecosystem restoration and sustainability can be broadly prioritized in countries and the world, then it could attract strong political support and commitment, thereby improving the livelihood of people living in rural areas around the world. This research was joint funded by the Second Scientific Expedition to the Qinghai-Tibet Plateau (grant no. 2019QZKK0405 ), the Innovative Team of Grassland Resources from the Ministry of Education of China ( IRT_17R59 ), and the Inner Mongolia Key Project ( ZDZX2018020 ). We thank the anonymous reviewers for reviewing this manuscript. The authors declare no competing interests.

Climate change may make semiarid grasslands increasingly prone to wildfire. We studied fire seasonality and growing season condition effects on a semiarid grassland in Southern Alberta, Canada. Plots were hand-torched in either fall or spring. Response variables estimated included plant composition and diversity, plant height, aboveground net primary production (ANPP), and forage nitrogen quality. The experiment was replicated over three consecutive growing seasons, and each replicate was monitored for 3 yr thereafter. Drought conditions occurred during two of the six growing seasons. Fall fires appeared to be hotter than spring fires based on a greater fuel mass (standing litter) and exposed the soil surface to a longer period without the benefit of standing litter over winter. Although this grassland is resilient to fire, compared with spring-burned grasslands, the species composition, ANPP, and leaf length of grasses of fall burned communities took a longer time to recover to preburn conditions. Our results suggest that spring-burned grasslands should not be grazed for 1 year post burn to allow time for recovery of ANPP and litter. However, given that ANPP of fall-burned communities also exhibited higher nitrogen concentration that may make the forage more palatable to livestock, and that these communities were more severely impacted, it seems prudent to delay their grazing for more than 1 year to prevent overgrazing. The negative impacts of fire on ANPP may be ameliorated with above-average precipitation in June, which may be forecast during an El Nino year. (C) 2021 The Author(s). Published by Elsevier Inc. on behalf of The Society for Range Management.

Crested wheatgrass (CWG) [Agropyron cristatum (L.) Gaertn.] is a commonly introduced grass in the Canadian prairies, but concerns remain about its possible long-term effects on soil quality, and its influence on soil water repellency (SWR) has not been determined. The long-term (24 yr) effects of CWG on SWR in comparison to seeded native grasses and annual cropping were determined for a clay loam soil in southern Alberta, Canada by measuring SOC concentration and SWR using soil hydrophobicity (SH) and soil water repellency index (RI) methods. The cropping treatments were CWG, seeded native grass mix (NGM), continuous wheat, and wheat–fallow rotation, each with fertilized (nitrogen) and non-fertilized subplots, replicated four times. Mean SOC concentration, SH, and RI in samples of surface soil were similar (P > 0.05) for CWG and seeded NGM, and they did not support our hypothesis (seeded NGM > CWG). Mean SOC was significantly greater for seeded perennial grasses than annual crops by 1.7–2 times and SH by 2.1–2.5 times, which supported our hypothesis, but RI was similar among treatments. As expected, nitrogen fertilization significantly increased SOC concentrations, but the effects on SH and RI were undetectable. A strong positive correlation occurred between SOC concentration and SH (r = 0.92) but not for RI (r = 0.10). Our findings suggested that SWR was similar for CWG and seeded NGM. The SWR as measured using SH was greater for seeded perennial grasses than annual cropping but was similar using RI.

Water repellency of agricultural crop residues may affect the hydrologic balance and increase runoff loss of pesticides by greater wash off from hydrophobic residue. We conducted a laboratory study to measure water repellency and hydrophobicity of 30 major agricultural crops (grass, legume, cereal, oilseed, pulse, and specialty crops). Crop samples were collected in southern Alberta, Canada in 2017 and 2018. Water repellency (WR) of oven‐dried (60°C) and ground (<2 mm) crop residues was measured using the water drop penetration time (WDPT) and molarity of ethanol (MED) tests. Hydrophobicity was evaluated using the ratio of hydrophobic CH– to hydrophilic CO–functional groups using Fourier Transform Infrared (FTIR) spectroscopy. The WDPTs of the 30 agricultural crops ranged from 8.3 to 2438 s, suggesting that crop species influenced WR of the dried and undecomposed residues. Needle‐and‐thread grass (Stipa comata Trin. and Rupr.), blue grama (Bouteloua gracilis [Kunth] Lag. ex Griffiths), and western wheatgrass (Agropyron smithii Rydb.) were the most WR crops based on WDPT. Fababean (Vicia faba), mustard (Sinapis alba L.), and sweet clover (Melilotus officinalis) were the least WR crops. Mean WDPTs were significantly (P ≤ 0.05) greater for grass than the other four crop types by 23 to 44 times. Significant differences in WDPT occurred among crop species within each of the six crop types. A significant positive correlation occurred between WDPT and hydrophobicity (r = 0.54), but not between WDPT and organic carbon. Overall, crop type and species may influence WR of crop residues and could affect the hydrologic balance.Core Ideas Agricultural crop species residue influenced water repellency and hydrophobicity Grass was the most water repellent and hydrophobic crop type A positive correlation occurred between water repellency and hydrophobicity The physical morphology of leaves may contribute to water repellency Water repellency differences also occurred for species within the six crop types

https://doi.org/10.2134/agronj2019.02.0067 The “McGhie and Posner (1980)” citation in the text and the accompanying reference citation “McGhie, D.A., and A.M. Posner. 1980. Water repellence of a heavy-textured Western Australian surface soil. Aust. J. Soil Res. 18:309–323.” were both incorrect. The correct reference citation in the text should be “McGhie and Posner (1981)”. The correct reference citation should be “McGhie, D.A., and A.M. Posner. 1981. The effect of plant top material on the water repellence of fired sands and water repellent soils. Aust. J. Agric. Res. 32:609–620.” The authors apologize for this error.

Stipa breviflora Grisb. (S. breviflora) is a dominant species in the desert steppe of northern China. Its function and role at the plant community level increases with increasing stocking rate. However, the response of spatial stability remains unclear. We selected treatment areas representing no grazing (CK), light grazing (LG), moderate grazing (MG) and heavy grazing (HG) in a long-term grazing experiment (2004-2017) in a S. breviflora desert steppe in Inner Mongolia, northern China. Using a mechanical sampling method, 40 m × 40 m representative sample plots were selected to obtain the height, coverage and density of the S. breviflora population and community, and we computed the standing crop of mechanical sampling quadrats based on a random sample of cutting quadrats. Analysis of standing crop, density of S. breviflora population and its ratio in the plant community showed that the dominant role of S. breviflora population in the plant community increased with increasing grazing intensity, while the spatial stability of S. breviflora population not only had many dimensions, but also many states. The dimension or combination of dimensions of its stability performance and its adaptive state varied under different disturbance intensities and frequencies.

Cultivating native rangeland can have detrimental effects on soil carbon and nitrogen storage. Understanding how vegetation and soil recover after returning marginal cultivated land to its native state is important since soil plays a key role not only in food production but also in regulating global climate change. Soil samples were taken from two sites, a mixedgrass and a dry mixedgrass prairie, which have different climates and plant species composition. Each study site included one undisturbed native plot (CK) and two cultivated treatments that were abandoned in 2008 after being cultivated for more than ten years prior to this study, one with continuous wheat (Triticwn aestivurn L.) and the other with wheat-fallow rotations. Soil organic carbon (SOC), total nitrogen (TN), and labile organic fraction content were measured in 2016, while plant coverage and species diversity were investigated in 2017. In both study sites, grass and sedge coverage in the previously cultivated treatments were lower than, with shrub and forb coverage similar to, the CK. The highest invasive species coverage appeared in the previously cultivated treatments. Species richness was higher with CK in the mixedgrass prairie but no differences were found in the more arid dry mixedgrass prairie. No differences were found among all treatments for species evenness, Simpson's index and Shannon Wiener index. On average, in the 0-15 cm depth, SOC and TN contents with the previous cultivated treatments were still 20% and 16% lower than CK, respectively, whereas in the 15-30 cm depth, SOC and TN contents did not differ among all treatments except for SOC content in the mixedgrass prairie. Relative to CK, previously cultivated treatments had similar active carbon (AC), microbial respiration-carbon and NH4+ -N contents but the mixedgrass prairie had lower water extractable-organic carbon and water extractable-nitrogen. In contrast, in the dry mixedgrass prairie all labile organic fraction contents, except for AC, were the same among all treatments. Negative relationships were found between plant diversity and surface soil carbon and nitrogen storage. Our results indicate that for short-term disturbed rangeland, 9 years is likely sufficient for the recovery of soil labile organic fractions and plant diversity but a longer time will be needed for the recovery of SOC and TN.

While northern temperate grasslands are important for supporting beef production, it remains unclear how grassland above- and belowground biomass responds to long-term cattle grazing. Here, we use a comprehensive dataset from 73 grasslands distributed across a broad agro-climatic gradient to quantify grassland shoot, litter, and shallow (top 30 cm) root biomass in areas with and without grazing. Additionally, we relate biomass to soil carbon (C) concentrations. Forb biomass was greater (p < 0.05) in grazed areas, particularly those receiving more rainfall. In contrast, grass and total aboveground herbage biomass did not differ with grazing (total: 2320 kg ha −1 for grazed vs. 2210 kg ha −1 for non-grazed; p > 0.05). Forb crude protein concentrations were lower (p < 0.05) in grazed communities compared with those that were non-grazed. Grasslands subjected to grazing had 56% less litter mass. Root biomass down to 30 cm remained similar between areas with (9090 kg ha −1 ) and without (7130 kg ha −1 ) grazing (p > 0.05). Surface mineral soil C concentrations were positively related to peak grassland biomass, particularly total (above + belowground) biomass, and with increasing forb biomass in grazed areas. Finally, total aboveground shoot biomass and soil C concentrations in the top 15 cm of soil were both positively related to the proportion of introduced plant diversity in grazed and non-grazed grasslands. Overall, cattle grazing at moderate stocking rates had minimal impact on peak grassland biomass, including above- and belowground, and a positive contribution exists from introduced plant species to maintaining herbage productivity and soil C.

Grasslands provide about half of the total feed for livestock production and support a large number of social and cultural ecosystem services around the world. Grazing livestock systems mostly depend on grasslands, but the production efficiency of this system is often very low. Improving the efficiency of grazing livestock systems while conserving grasslands is a great challenge. One large size on-farm experiment with traditional whole-year grazing and a lower stocking rate summer animal grazing plus three months of greenhouse feeding was carried out in grassland areas of northern China. Ecological sites were classified and their aboveground biomass was estimated with ground measurements and remote sensing technology. Models of balance of forage supply and animal requirements, and the optimization of grazing livestock system were used to understand the current situation of the grazing livestock system, and to find an improved way to manage grazing livestock system. Finally, we worked with a private company and some herders to upscale adoption of the results in a wider area. The results indicated that a lower stocking rate during summer grazing plus greenhouse feeding in winter is a suitable improved grazing livestock system in pastoral areas in northern China. This management system is innovative in that it both enhances livelihood outcomes and conserves the grazing lands. The key points for this new system are estimation of forage and feed supply and animal requirements, grazing livestock management improvement (such as the low stocking rate plus winter greenhouse feeding) assessed based on maximum net income, integration of Dorper sheep and improved management.

Grazing activity can profoundly influence grassland plant community structure and ecosystem functions. However, our understanding of the effects of livestock grazing on ecological stability across different grassland types remains limited. Based on a 5-year investigation along a precipitation gradient (180 mm in desert steppe, 282 mm in typical steppe and 375 mm in meadow steppe) in temperate grasslands of Inner Mongolia, we examined the responses of the temporal stability of plant community aboveground biomass to grazing intensity at three levels (light grazing, moderate grazing and heavy grazing). We found that grazing intensity at all levels reduced biomass temporal stability across all types of grasslands. Heavy grazing intensity reduced community biomass, species richness and species asynchrony. Structural equation modeling further revealed that grazing decreased community stability mainly by decreasing species asynchrony. In addition, community-level stability was driven by grass species stability in the meadow steppe, but it was affected by the stability of forb species in the desert steppe. These findings suggest that grazing practices may alter the stability properties of grassland plant communities, highlighting the importance of understanding changes in different plant functional groups for predicting community dynamics under grazing management.

Management intensive grazing (MIG) may not maximize plant productivity on rangelands because of morphophysiological traits of grassland vegetation. We examined defoliation and moisture effects on the biomass yield of rhizomatous and caespitose grass pairs that were either phylogenetically similar or of similar agroclimatic adaptation, including two agronomic grasses. From relatively low to high moisture regime adaptation, species pairs included western wheatgrass (Pascopyrum smithii [Rydb.] A. Love) and needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkw.), northern wheatgrass (Elymus lanceolatus [Scribn. & J.G. Sm.]) and western porcupine grass (H. curtiseta [Hitchc.] Barkw.), plains and foothills rough fescue (Festuca hallii [Vasey] and F. campestris Rydb.), and smooth and meadow brome (Bromus inermis Leyss. and B. riparius Rehm). Response variables were shoot yield, root-shoot ratio, and water-use efficiency. We hypothesized that caespitose grasses, regardless of their origin or adaptation to agroclimate regime, would respond more determinately in biomass accumulation. Defoliation effects on shoot biomass were more pronounced under high moisture. Low intensity−high frequency defoliation yielded similarly to deferred controls in all grasses, and the same was true for high-intensity−low-frequency (HILF) defoliation in 1 rhizomatous grass. Three of the 4 rhizomatous grasses and 1 caespitose grass yielded greater under HILF defoliation compared with high-intensity−high-frequency defoliation. Caespitose grasses allocated more biomass to roots under low moisture conditions. Water-use efficiency decreased under high moisture conditions and more intense and/or frequent defoliation and peaked in agronomic grasses. Overall, our results suggested that growth patterns corresponded more with phylogenetic similarity as opposed to growth form. A conceptual model from these results showed that across all species, only the introduced bromes generated greater biomass under HILF defoliation, and this may explain why past research consistently concludes that MIG does not enhance plant productivity on rangelands.

Unmanaged riparian grazing may negatively impact rivers. The objective was to determine the influence of riparian grazing by cattle on selected channel morphology properties and riparian health of the Lower Little Bow River in southern Alberta. Three study reaches with increasing levels of riparian grazing impact were selected: (1) a fenced reach with cattle exclusion (2001-2012) followed by two years (2013-2014) of periodic grazing of the riparian pasture, (2) an unfenced and grazed reach with low cattle impact, and (3) an unfenced and grazed reach with high cattle impact. Selected channel morphology properties were measured for 3 years (2013-2015), and streambank erosion was measured over 6 years (2009-2014). The riparian health of the fenced reach was also assessed before and after 4, 8 and 11 yr of cattle exclusion, and then after 2 yr of periodic grazing. The findings generally supported the hypothesis that reduced or no riparian grazing impact would significantly (P <= 0.10)increase bank undercut, water depth, bankfull depth and mean-weight diameter of riverbed sediment, and decrease flow width, flow width:depth ratio, bankfull width, bankfull width: depth ratio and bank erosion. The overall riparian health score of the fenced reach was increased from 65% (healthy but with problems) prior to fencing to 85% (healthy) after 11 yr of cattle exclusion, but then decreased to 78% (healthy but with problems) after two years of periodic grazing. Exclusion fencing generally improved most channel morphology variables and riparian health. However, non-utilization of the forage resource, excess litter build-up and greater fire risk, and increased disturbance-caused plants and invasive species were serious management concerns. These issues might be alleviated by periodic grazing of the riparian pasture, but the long-term effect of this practice on channel morphology and riparian health requires further research.

Rotational stocking theoretically enables regrazing of regrowth, but regrowth may be limited in xerophytic vegetation. We tested the hypothesis that regrowth would be slow and fixed in Hesperostipa comata (a caespitose, drought-tolerant grass), while growth would be flexible in Pascopyrum smithii (a rhizomatous, less drought-tolerant grass) under increasing defoliation and moisture, by assessing tiller growth rates, population dynamics and plant yield on marked plants in a Dry Mixed Grass prairie. Plots were clipped in late summer to simulate a deferred control, or intermittently during the growing season (May–August) at high intensity–low frequency (HILF), low intensity–high frequency (LIHF) or high intensity–high frequency and crossed with two water treatments (ambient and addition) in both a xeric upland and a mesic lowland. Growing season defoliation increased tiller growth rates of P. smithii in the upland, whereas HILF and LIHF reduced growth in the lowland. All defoliation regimes increased tiller growth for H. comata. Tiller populations of H. comata increased with frequent defoliation, while tiller populations of P. smithii decreased regardless of defoliation regime. Frequent defoliation, regardless of intensity, reduced yield relative to the deferred control for both grasses. While water addition consistently increased growth rates and reduced differences in tiller number among defoliation treatments, the regrowth of both grasses remained similar under varied defoliation with ambient moisture. High moisture conditions also promoted regrowth more in P. smithii compared to H. comata. In summary, neither grass species displayed an inherently fixed or flexible tiller or plant yield response in response to defoliation or moisture.

Little is known about the specific role of exotic species on measures of grassland plant diversity, including how this may vary with climatic conditions or large mammal herbivory. This study examined vegetation responses to long-term livestock grazing, including plant richness and diversity, as well as the contribution of exotic species to these metrics, across a network of 107 northern temperate grasslands in Alberta, Canada, spanning a broad aridity gradient. Exposure to grazing modestly increased plant richness, but did not alter Shannon’s diversity, Simpson’s diversity, or evenness, suggesting stability in floral diversity relative to grazing. However, grazing did increase grass cover while reducing shrub cover, the latter of which was only apparent in mesic grasslands. Unlike total plant diversity, exotic species richness and cover, together with exotic plant contributions to diversity, varied jointly with grazing and aridity. While long-term grazing increased exotic species, this response was most apparent in wetter areas, and non-grazed grasslands remained more resistant to the presence of exotics. Several exotic species were positive indicators of grazing in wetter grasslands, and coincided with lower native species cover, indicating grazing may be facilitating a shift from native to exotic vegetation under these conditions. Overall, our results indicate that while long-term grazing has altered the composition and cover of certain functional groups, including favoring exotics and minimizing woody vegetation in mesic areas, overall changes to plant diversity were limited. Additionally, these findings suggest that semi-arid northern temperate grasslands remain relatively resistant to grazing effects, including their susceptibility to exotic plant encroachment. These results improve our understanding of how ongoing grazing exposure may impact grassland diversity, including efforts to conserve native vegetation, as well as the important role of climate in altering fundamental grassland responses to grazing.

Grasslands cover more than 40% of the terrestrial surface of Earth and provide a range of ecological goods and services, including serving as one of the largest reservoirs for terrestrial carbon. An understanding of how livestock grazing, influences grassland soil organic carbon (SOC), including its concentration, vertical distribution and association among soil-particle sizes is unclear. We quantified SOC concentrations in the upper 30 cm of mineral soil, together with SOC particle-size association, within 108 pairs of long-term grazed and non-grazed grassland study sites spanning six distinct climate subregions across a 5.7 M ha area of Alberta, Canada. Moderate grazing enhanced SOC concentration by 12% in the upper 15 cm of soil. Moreover, SOC concentrations in mineral layers were associated with regional climate, such that SOC increased from dry to mesic subregions. Our results also indicate that C concentrations in each of 2000–250, 250–53, < 53 μm soil particle-size fractions were consistent with total SOC concentrations, increasing from semi-arid to more mesic subregions. We conclude that long-term livestock grazing may enhance SOC concentrations in shallow mineral soil and affirm that climate rather than grazing is the key modulator of soil C storage across northern grasslands.

Off-stream waterers (OSWs) located in upland pastures may be effective in reducing livestock impacts on riparian areas and rivers, but little research has been conducted on the impact of OSWs located closer to rivers. We studied cattle behaviour over four years (2012-2015) for a portable OSW at two sites (18-25 m from river) along an unfenced reach, and two permanent OSWs (41-68 m from river) located adjacent to the fenced reach with restricted cattle-access along the Lower Little Bow River in southern Alberta. The number of cattle drinking from the OSW versus river or restricted access site, as well as number of cattle on the bench-terrace or riparian zone with and without OSW, was determined. Significantly (P <= 0.10) greater (15-fold) number of cattle per day preferred to drink from the OSW compared to the river at the first location (Site 1) along the unfenced reach in June of 2012, but there was no significant difference at the second location (Site 2) along this same reach in July-August of 2012. Significantly greater (1.7-3.4 fold) numbers of cattle were present on the bench-terrace than the riparian zone when the OSW was present along the unfenced reach. Similar number of cattle preferred to drink from the OSW and restricted river-access site along the south side of the fenced reach in 2013 and 2015, and greater (2.7 fold) number preferred to drink from the river than OSW in 2014. In contrast, the permanent OSW on the north side of the fenced reach had significantly more (2.7 fold) cattle preferring to drink from the OSW than river-access site in 2015. Our results generally supported the hypothesis that OSWs located closer (<= 68 m) to rivers were effective, but there were some exceptions.