No Grazing Research Articles

Carbon dioxide fluxes and soil carbon storage in relation to long‐term grazing and no grazing in Icelandic semi‐natural grasslands

AbstractQuestionWhat is the effect of long‐term grazing and no grazing (NG) on carbon dioxide flux and soil carbon storage in Icelandic semi‐natural grasslands.LocationThree farms, with known history of land use, in W Iceland.MethodsOn each farm, we located an intensively and an extensively grazed site, which both had been constantly grazed for centuries, and a parallel site with no grazing for over 50 years. We measured net ecosystem exchange (NEE), ecosystem respiration and normalized difference vegetation index on a regular basis over the growing season. Samples were taken from 60 cm deep soil profiles for analysis of soil organic carbon (SOC).ResultsThe grazed sites showed significantly more negative NEE than the NG sites, indicating more carbon dioxide uptake on the grazed sites compared to the NG sites. The normalized difference vegetation index was also significantly higher on the grazed sites. On all farms, the total SOC content was higher in the grazed sites than in the parallel NG sites.ConclusionsThe study indicates that cessation of grazing decreases productivity and carbon dioxide uptake in a semi‐natural grassland in Iceland, as well as SOC content in the soil. Historically, all the NG sites in the study had the same grazing history as the continuously grazed sites until grazing exclusion. The measured lower SOC on the NG sites seems to indicate that, without grazing, SOC is lost with time and/or grazing is needed to maintain SOC in these grasslands.

Different responses of soil element contents and their stoichiometry (C: N: P) to different grazing intensity on the Tibetan Plateau shrublands

Potentilla fruticosa, a major alpine shrubland type, is widely distributed across the Tibetan Plateau, and grazing is the most common disturbance in the shrublands of P. fruticosa. However, soil organic carbon (SOC), soil total nitrogen (STN), soil total phosphorus (STP), and their stoichiometry under different grazing intensities were unclear. In our study, we explored SOC, STN, STP, their stoichiometry, and their controlling factors in the grazing disturbance of heavy grazing (HG), moderate grazing (MG), light grazing (LG), and no grazing (NG) conditions in the Tibetan Plateau P. fruticosa shrublands. The grazing intensities were mainly assessed by considering the shrublands’ ground cover, the indicators of the road density, the distance between sampling sites and cowshed or sheep shed, the amounts of cow and sheep dung, and vegetation that had been gnawed and stampeded. Our results indicated that soil physical properties of soil temperature and bulk density have decreasing trends with decreasing grazing intensities from HG to NG. The SOC, STN, STP, and soil C:N and C:P ratios have increasing trends with decreasing grazing intensities from HG to NG, while the changes in soil N:P ratio were relatively stable along grazing intensities. Our results indicated that HG generally had stronger effects on SOC, STN, and soil C:N and C:P ratios than NG, indicating substantial effects of grazing disturbance on biogeochemical cycles of SOC and STN in the shrubland ecosystems. Therefore, for the alpine shrubland of P. fruticosa, the HG should be avoided for sustainable cycling of soil nutrients and the balance of soil nutrient stoichiometry. The grazing types can directly affect plant conditions, and plant conditions can directly affect soil physical and chemical properties and litter standing crops. Finally, soil physicochemical properties and litter standing crop resulting from different grazing intensities directly control SOC, STN, and STP. For the soil stoichiometry, the soil’s physical and chemical properties resulting from different grazing intensities have direct impacts on soil C:P and N:P ratios.

Impact of cattle grazing corn residue in spring on soil and subsequent soybean yield

AbstractThe effects of spring corn (Zea mays) residue grazing and stocking density on soil physical properties and subsequent soybean (Glycine max) yield were evaluated in an experiment with three treatments: no grazing (NG), normal stocking density (NSD), and high stocking density (HSD). The study was conducted over 2 years with four replicates per treatment each year. Steers (277 ± 4.4 kg) were stocked at 7.5 steers/ha for NSD with a target grazing of 45 days starting in mid‐February, and 22.5 steers/ha for HSD with a target grazing of 15 days in mid‐March, such that the stocking rate was equal. Bulk density, penetration resistance, and surface roughness were measured pre‐ and post‐planting. At 0‐to‐5‐ and 5‐to‐10‐cm depths, bulk density and penetration resistance were greater (p < 0.01) for NSD than NG. There was no difference in bulk density (p ≥ 0.45) between grazed treatments. At 0–5 cm, penetration resistance was not different (p = 0.29) between grazed treatments. For 5–10 cm, penetration resistance was greater (p = 0.02) for HSD compared to NSD. Surface roughness was greater (p < 0.01) for NSD than NG, and greater (p < 0.01) for HSD than NSD. There was no difference (p ≥ 0.34) in soybean emergence among treatments. Soybean yield was less (p < 0.01) for NG than NSD, but did not differ (p = 0.06) between NSD and HSD. The results indicate that spring grazing may cause minor compaction without reducing subsequent soybean yield.

Adaptive grazing and animal density implications for stocking rate and drought in northern mixed-grass prairie

Grazing management is critical for ruminant livestock enterprises affecting both animal performance and land sustainability. Intensification of grazing management is important for increasing food production, however, linear stocking rate models are not ideal in rangeland environments due to complexities such as drought. We conducted a study in a semiarid northern mixed-grass prairie in Wyoming, USA from 2017 to 2021. Grazing treatments were moderate rotational grazing (MRG; 4 heifers), ultra-high density rotational grazing (UHD; 33 cow-calf pairs), and no grazing (NG) organized in a randomized complete block design using 0.4 ha paddocks. Baseline vegetation was measured prior to grazing each year to determine grazing time available using a modified Robel pole coupled with forage biomass clippings. Planned and realized stocking rates were then calculated for all MRG and UHD treatments and potential stocking rates for NG and relativized to effective precipitation (March 1 to timing of sampling in mid-June). For the UHD treatment, cattle time in paddocks ranged from 0.29 to 1 d while for the MRG treatment, cattle time in paddocks ranged from 4.5 d to 12.5 d Effective precipitation ranged from 130 mm in 2020 to 251 mm in 2018 with a five year mean of 205.4 mm. Planned/potential stocking rate ranged from 1.40 to 5.17 Animal Unit Months per hectare (AUMs ha−1) and realized stocking rate ranged from 1.38 to 4.87 AUMs ha−1 across paddocks and years. Vegetation visual obstruction and stocking rate did not differ by treatment any of the years of the study (all p-values > 0.05) with the exception of 2020 when the NG treatment was higher than the MRG and UHD treatments (p < 0.05). Planned and realized stocking rates for both grazing treatments had highly correlated (both r2-values ≥ 0.80) and significant relationships (both p-values < 0.05) with effective precipitation. Five year mean planned or realized stocking rates did not differ by treatment. Accomplishing planned stocking rates proved to be difficult for the UHD grazing scheme that requires rapid moves as indicated by the broader range of ΔAUMs ha−1 (Planned – Realized) in that treatment compared to the MRG treatment. The effect of precipitation on stocking rates, and specifically relative to potential stocking in the NG treatment, was most influential during the significant deficit year but was non-existent during average years or surplus years. Using annual visual obstruction readings (VOR) to adapt stocking rates may be useful for more intense grazing management.

Effects of seasonal grazing on plant and soil microbial diversity of typical temperate grassland.

Biodiversity is the decisive factor of grassland ecological function and process. As the most important human use of grassland, grazing inevitably affects the grassland biodiversity. However, comprehensive studies of seasonal grazing on plant and soil bacterial, archaeal and fungal diversity of typical temperate grassland are still lacking. We examined the impact of seasonal grazing, including no-grazing (NG), continuous grazing (CG), grazing in May and July (G57), grazing in June and August (G68), and grazing in July and September (G79) on grassland plant and soil microbial diversity based on a long-term field grazing experiment. The results showed that the aboveground plant biomass (AGB) of the seasonal grazing plots was significantly higher than that of the CG plots. Compared with NG, CG increased significantly the Margalef richness index of plant community, while did not significantly change the Shannon, Simpson and Pielou evenness of plant community. Grazing changed the composition and biomass of dominant vegetation. Long-term grazing decreased the proportion of Leymus chinensis (Trin.) Tzvel. and increased the proportion of Cleistogenes squarrosa (Trin.) Keng. There was no significant change in the Shannoneven, Shannon and Coverage indices of soil bacteria, archaea and fungi between NG and the grazing plots. But the Chao index of soil fungi in G57, G68 and G79 and archaea in G57, G79 was significantly higher than that in CG. The results of correlation analysis showed that the plant diversity in the CG plots was significantly negatively correlated with the soil bacterial diversity. The plant richness in the G57 and G68 plots was significantly positively correlated with the soil archaea richness. Our study showed that seasonal grazing was a sustainable grazing management strategy for maintaining typical grassland plant and soil microbial diversity in northern of China.

Effect of grazing intensity on alpine meadow soil quality in the eastern Qinghai-Tibet Plateau, China

Grazing plays a critical role in the sustainable development of grassland. It has been convinced that grazing affects grassland productivity, however, researches on the relationship between grazing intensity and grassland soil quality remain inadequate in the alpine environment. This study compared ten soil quality indexes (SQIs) to quantitative assess the effect of different grazing intensities [no grazing (NG); light grazing (LG); moderate grazing (MG); heavy grazing (HG)] on the soil quality of alpine meadow in the 0–10 cm and 10–20 cm soil layers. Principal component analysis (PCA) and minimum data set (MDS) were applied to indicator selection and weight assignment. The fitting relationship and correlation between SQI-TDS and SQI-MDSs and the sensitivity index (SI) of ten SQIs were used to select the optimal SQI method. Our results showed that compared with NG and LG, HG and MG significantly decreased soil organic matter (SOM), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), and cation exchange capacity (CEC) (p < 0.05), whereas increased bulk density (BD) and pH. Besides, TN, TP, TK, SOM, Sand content, soil phosphatase activity (PHO), soil sucrase activity (SUC), and soil catalase activity (CAT) could well replace the TDS method to evaluate soil quality. The SQI calculated by the MDS4 with the non-linear scoring method (SQI-NL-MDS4) had the best performance in soil quality evaluation among ten SQIs. Compared with NG and LG, HG had a stronger negative effect on alpine meadow soil quality, especially in the 0–10 cm soil layer, which potentially aggravated leading to aggravating grassland degradation. We propose that reasonable grazing intensity management should be advocated to maintain the sustainable development of alpine meadow productivity.

Growth-Defense Trade-Offs Induced by Long-term Overgrazing Could Act as a Stress Memory.

Long-term overgrazing (OG) is one of the key drivers of global grassland degradation with severe loss of productivity and ecosystem functions, which may result in stress memory such as smaller stature of grassland plants. However, how the OG-induced stress memory could be regulated by phytohormones is unknown. In this study, we investigated the changes of four phytohormones of cloned offspring of Leymus chinensis that were developed from no-grazing (NG) plants and OG plants with a grazing history of 30 years. The concentrations of auxin (IAA) and gibberellic acid (GA) in OG plant leaves were 45% and 20% lower than control, respectively. Meanwhile, the level of abscisic acid (ABA) in OG leaves nearly doubled compared with that in NG leaves. The situation was quite similar in roots. Unexpectedly, no significant changes in the jasmonic acid (JA) level were observed between OG and NG plants. The changes in gene expression patterns between OG and NG plants were also investigated by transcriptomic analysis. In total, 302 differentially expressed genes (DEGs) were identified between OG and NG plants, which were mainly classified into the functions of synthesis, receptor, and signal transduction processes of phytohormones. The expression of 24 key genes related to the biosynthesis and signal transduction of IAA and GA was downregulated in OG plants. Among them, OASA1 and AO1 (regulating the biosynthesis of IAA and ABA, respectively) were reduced significantly by 88 and 92%, respectively. In addition, the content of secondary metabolites related to plant defense such as flavonoids and phenols was also increased in leaves. Taken together, the decrease of positive plant growth-related hormones (IAA and GA) together with the increase of plant stress-related hormones or factors (ABA, flavonoids, and phenols) induced the growth-defense trade-offs for L. chinensis adaptation to long-term OG stress. The findings reported in this study shed new light on the mechanism of plant–animal interaction in the grassland ecosystem and provide a deeper insight into optimizing grazing management and sustainable utilization of grassland.

The Role of Plant Functional Diversity in Regulating Soil Organic Carbon Stocks under Different Grazing Intensities in Temperate Grassland, China

Grazing is very common in the grassland ecosystem, and it has a significant impact on the C stocks and cycle. One of the most important drivers of soil C stocks is functional diversity. However, limited studies have attempted to explore the effects of functional diversity on soil C stocks associated with grazing disturbance. This study was carried out in Hulunbeier grassland, Inner Mongolia, and four grazing intensities (no grazing (NG), light grazing (LG), moderate grazing (MG), and heavy grazing (HG)) were identified. The plant functional traits and important soil properties under different grazing intensities were measured. Functional identity and diversity were calculated based on the measured functional traits. The impacts of functional identity and diversity on soil organic carbon stocks (SOCstocks) were analyzed using a multi-model inference (MMI) approach. Our study showed that the functional diversity effect on soil C stocks varies depending on grazing intensity. We identified that functional richness has a significant impact on SOCstocks in NG. The community weighted mean of leaf area became the best predictor of SOCstocks in LG. As grazing intensified, functional divergence best explained SOCstocks in moderate and heavy grazing sites, and their relationship was positive. The major outcomes of this research could shed light on the mechanics of soil carbon storage.

20 Forage Production and Nutritive Quality of Dual-purpose Wheat Managed Under Three Different Grazing Frequencies in the Southeastern United States

Abstract Grazing of dual-purpose wheat is an established management system in the Great Plains regions of the United States. Varietal and climatic differences between regions has limited use of dual-purpose systems in the Southeast. The objective of this study was to evaluate four wheat varieties, [feed wheat (mixed variety, Feed), seed wheat (‘GA Gore’) and two forage varieties, ‘AGS 2024’ (AGS) and ‘Pioneer 26R41’ (Pioneer)], under three grazing treatments [no-grazing (NG), low frequency (LF), high frequency (HF)]. The experiment was a randomized complete block design (n = 4) using mob-grazing. Forage samples were taken using three 0.1m2-quadrats before (Pre) and after (Post) each grazing event. Crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined on all Pre samples. Wheat grain yield was determined at the end of the season. Data were analyzed using PROC GLIMMIX of SAS (SAS Inst., Cary, NC), a &amp;lt; 0.05. Pre-grazed, AGS seasonal forage production was greater (P &amp;lt; 0.01) than all other varieties (1,517 kg/ha vs 1,031 kg/ha, respectively). Post-grazing biomass from AGS and Pioneer was greater than GA Gore (817 vs 512 kg DM/ha, respectively; P = 0.04). Pre-grazing, Feed, GA Gore and Pioneer had greater (P &amp;lt; 0.01) CP than AGS (31.6 vs. 30.1%, respectively). The concentration of NDF was greatest for AGS (39.1%) compared with all other varieties (34.9%, P &amp;lt; 0.01). Grazing frequency did not affect CP (P = 0.67). The NG plots had greater NDF and ADF than LF and HF (37.5 vs. 35.2% and 19.8 vs. 18.6%, respectively; P &amp;lt; 0.01). Pioneer had the greatest grain yield but was not different from AGS (57.6 and 52.4 kg/ha, respectively; P = 0.41). Management of wheat as a dual-purpose crop is feasible in the Southeast. More information is needed to determine the economic impact of this management practice.

Quantifying the immediate response of the soil microbial community to different grazing intensities on irrigated pastures

Grazing is known to affect soil microbial communities, nutrient cycling, and forage quantity and quality over time. However, a paucity of information exists for the immediate changes in the soil physicochemical and microbial environment in response to different grazing strategies. Soil microbes drive nutrient cycling and are involved in plant-soil-microbe relationships, making them potentially vulnerable to plant-driven changes in the soil environment caused by grazing. To test the hypothesis that variable grazing intensities modulate immediate effects on the soil microbial community, we conducted a grazing trial of three management approaches; high-intensity, short-duration grazing (HDG), low-intensity, medium-duration grazing (LDG), and no grazing (NG). Soil and vegetation samples were collected before grazing and 24h, 1 week, and 4 weeks after HDG grazing ended. Soil labile carbon (C) and nitrogen (N) pools, vegetation biomass, and soil microbial diversity and functional traits were determined, including extracellular enzymatic assays and high-throughput sequencing of the bacterial 16S rRNA and fungal ITS2 regions. We found that labile soil C and inorganic N increased following LDG grazing while C-cycling extracellular enzymatic activities increased in response to HDG grazing but both total extracellular enzymatic activity profiles and soil abiotic profiles were mostly affected by temporal fluxes. The soil fungal community composition was strongly affected by the interaction of sampling time and grazing treatment, while the soil bacterial community composition was largely affected by sampling time with a lesser impact from grazing treatment. We identified several key fungal taxa that may influence immediate responses to grazing and modulate plant-soil-microbe interactions. There was strong evidence of temporal influences on soil biogeochemical variables and the soil microbiome, even within our narrow sampling scheme. Our results indicate that the soil ecosystem is dynamic and responsive to different grazing strategies within very short time scales, showing the need for further research to understand plant-soil-microbe interactions and how these feedback mechanisms can inform sustainable land management.

Effects of livestock and wildlife grazing intensity on soil carbon dioxide flux in the savanna grassland of Kenya

Although grazing is the primary land use in the savanna lowland of southern Kenya, the effects of grazing on soil carbon dioxide flux (RS) remain unclear. A 12-month study was conducted from January to December 2020 on the effects of six grazing intensities sites (overgrazed (OG), heavily grazed (HG), moderately grazed (MG), moderately to lightly grazed (M-LG), lightly grazed (LG) and no grazing (NG)) on RS on. A camera trap was used to monitor the total number of animals at each site, indicating the grazing intensity. Weekly measurements of RS were taken using static greenhouse gas chambers along with simultaneous measurements of soil temperature (TS) and volumetric soil water content (WS) (depth of 5 cm). Mean RS at HG, MG, M-LG and LG sites was approximately 15–25% higher than at NG and OG sites (p < 0.001). Mean WS increased with decrease in grazing especially in the dry season, while TS increased with increase in grazing. We observed bimodal temporal variation in RS and WS due to two wet seasons in the year. Thus, variation in RS across the study period followed the changes in WS rather than those in TS. Mean values of RS in the wet seasons were significantly higher (>45%) than those in the dry seasons, and WS accounted for 71% of the temporal variability in RS (p < 0.05). In addition, the enhanced vegetation index (EVI, interpreted as a proxy for vegetation cover) explained 60% of the variance of RS, and WS and EVI together explained 75%. EVI showed a negative relationship (p < 0.05) with animal intensity, indicating that more grazing reduced vegetation cover and, consequently, soil organic carbon and biomass. Soil bulk density was lower at less grazed sites. While RS variability was unaffected by total nitrogen content, pH, and texture, correspondence analysis demonstrated that the main factors influencing RS dynamics across the year under different grazing intensities were WS and vegetation cover. Our results contribute to closing the existing knowledge gap regarding the effects of grazing intensity on RS in East Africa savannas. Therefore, this information is of great importance in understanding carbon cycling in savanna grassland, as well as the identification of the potential consequences of increasing land pressure caused by rising livestock numbers, and will assist in the development of climate-smart livestock management in East Africa.

Forms and balance of soil potassium from a long-term integrated crop-livestock system in a subtropical Oxisol

The presence of animal grazing at different intensities in integrated crop livestock systems (ICLS) may affect the forms and the balance of K in the soil, especially after many years. The objective of this study was to evaluate different K forms and their balance for 17 years with ICLS. ICLS experimental area used no-till practices with different grazing intensities of cattle in winter pasture (black oat + annual ryegrass) and soybean production in the summer season. The experiment started in May 2001 at a location with a Rhodic Hapludox (Oxisol). The treatments consisted of varied grazing intensities: intensive grazing (IG) at 10 cm of pasture height, moderate grazing (MG) at 20 cm of pasture height, and a no grazing (NG) treatment. The experimental design was a randomized block design with three replicates. Soil samples were collected in 2001, 2007, 2012 and 2017 in 0−5, 5−10, 10−15 and 15−20 cm of soil layers. Desorption of K was measured using the Mehlich-1 method and the results were fitted to first-order kinetic equations to obtain readily and potentially available K content. Total K was determined by X-ray fluorescence, and the unavailable K by the difference between the total K and potentially available K. Long-term no-till ICLS resulted in an increase in more readily available K forms in the soil surface. The increase was especially prominent in the no-grazing treatment due to the greater amount of K left in the plant residues. Regardless of grazing intensity, soybean cultivation was the controlling component of the soil nutrient budget, representing 98.6 % of the total amount of K exported. Animal outputs represent only 1.4 % of total K exported and are therefore the recycling component of the system. Although meat production in ICLS represents only a very small fraction of the amount of K exported from the system, K tends to become less available in the grazed treatments in the long-term.

Abundance and Diversity of Dung Beetles (Coleoptera: Scarabaeoidea) as Affected by Grazing Management in the Nebraska Sandhills Ecosystem.

Dung beetles (Coleoptera: Scarabaeoidea) serve a significant role in regulating ecosystem services on rangelands. However, the influence of grazing management on dung beetle communities remains largely unknown. The purpose of this study was to investigate dung beetle abundance and diversity throughout the grazing season in the Nebraska Sandhills Ecoregion. Grazing treatments included: continuous grazing (CONT), low-stocking rotational grazing (LSR), high-stocking rotational grazing (HSR), and no grazing (NG). The abundance and diversity of dung beetles were measured in the 2014 and 2015 grazing seasons using dung-baited pitfall traps. Dung beetle abundance for each grazing treatment was characterized through four indices: peak abundance, species richness, Simpson’s diversity index, and Simpson’s evenness. A total of 4,192 dung beetles were collected through both years of trapping in this study. Peak abundance and species richness were greater in grazed treatments when compared to NG in both years. Peak abundance in the HSR was 200% (2014) and 120% (2015) higher than in the LSR. Species richness in the HSR was 70% (2014) and 61% (2015) higher than in the LSR, and 89% (2014) and 133% (2015) higher than in CONT. Simpson’s diversity index was lower in the NG and CONT treatments when compared to the LSR or HSR treatments for both years. We conclude that rotational grazing, regardless of stocking density, promoted dung beetle abundance and diversity within the Nebraska Sandhills Ecoregion.

Grazing Effects on Soil Physical and Chemical Properties

Uncontrolled grazing can have deteriorative effects on soil properties. This paper studied the effect of different grazing intensities on soil physicochemical and hydraulic properties at Al-Khanasry Agricultural Station, Al-Mafraq, Jordan. In summer 2016. Treatments were (1) no-grazing (NG), (2) controlled grazing (CG), and (3) uncontrolled grazing (UnG) sites. Soil samples were collected from each site to determine bulk density (BD), aggregate stability (AS), soil organic matter (SOM), electrical conductivity (EC), soil acidity (pH), and cation exchange capacity (CEC). Infiltration (F (t)) and hydraulic conductivity (HC) were measured in the field. Results showed that UnG significantly increased BD, Controlled and un-controlled grazing sites showed similar BD (P=&lt; 0.05), the highest was in controlled grazing (1.47 g cm-3). Aggregate stability also increased under grazing condition (P=&lt; 0.05) only in the surface layer (AS), The lowest AS in surface layer was observed in no-grazed plot (17.4%), while no significant difference (P=&lt; 0.05) were observed between controlled and un-controlled grazing plots (24.6 and 24.8%), respectively. In significant (P=&lt; 0.05) Grazing increased soil OM in surface layers. Un-controlled grazing area had significantly (P=&lt; 0.05) higher OM content (3.5%) compared to the no-grazed, but not significant (P=&lt; 0.05) from the controlled grazing area (3%). Grazing significantly decreased F(t) and HC when compared to NG. Grazing significantly (P=&lt; 0.05) reduced cumulative infiltration. The highest cumulative infiltration was observed in no-grazed area while the lowest was in un-controlled grazing area. Also, significant results showed that Grazing reduced (HC), however no significant (P=&lt; 0.05) differences were observed between controlled and un-controlled grazing areas (P=&lt; 0.05). The higher HC was in no-grazed site (0.172*103 cm s-1) while the lowest was in un-controlled grazing area (0.034*103 cm s-1). Therefore, controlling grazing intensity is recommended in these dry areas.

Effect of Grazing Types on Community-Weighted Mean Functional Traits and Ecosystem Functions on Inner Mongolian Steppe, China

The relationships between community-weighted mean (CWM) functional traits and ecosystem functions have been extensively studied. However, how CWM traits and ecosystem functions respond to grazing types and whether the relationships between CWM traits and ecosystem functions mediate the response of ecosystem functions to grazing types remains controversial. In the present study, we set up a seven-year grazing experiment with four grazing types: no grazing (NG), cattle grazing (CG), sheep grazing (SG), and mixed grazing by sheep and cattle (MG) on Inner Mongolia grassland. Nine functional traits of dominant species and five ecosystem functions under different grazing types were determined, and the relationships between CWM traits and ecosystem functions were analyzed. The results showed that the CWM height decreased after grazing, while the CWM nitrogen and phosphorus contents increased after CG. SG caused a greater decrease in aboveground biomass (AGB) and a greater increase in the net ecosystem CO2 exchange (NEE) of grassland ecosystems than did CG. This result may be partially because the CWM nutrient content and NEE were more negatively related after CG; and the increase in the CWM nitrogen and phosphorus contents suppressed NEE after CG. Therefore, to protect the sustainability of grassland ecosystem functions, SG should be reduced. Additionally, our work emphasizes that the relationships between plant functional traits and ecosystem functions may mediate the response of ecosystem functions to grazing types.

Linking phytogenic hillocks with plant ecological strategies in a desert steppe: Adaptation of Stipa breviflora to heavy grazing

Abstract The relationship between plants and phytogenic hillocks in arid ecosystems is receiving increasing attention. Although ecologists have explored the microsystem relationship between plant ecological strategies and phytogenic hillocks, the explanation is still ambiguous due to the lack of relevant information on desert grasslands under grazing disturbance. In the present study, a constructive species, Stipa breviflora (a perennial bunchgrass), was selected as the research object in a desert steppe in northern China to quantify plant traits (i.e., height, density, biomass, and seed production) in different growth phases and epiphytically phytogenic hillock traits (i.e., length, width, height, seed number, and soil nutrients) under heavy grazing (HG), moderate grazing (MG), and no grazing (NG). Immature S. breviflora formed phytogenic hillocks under HG treatment. The phenotypic characteristics of phytogenic hillocks were significantly related to the number of aggregated seeds. Furthermore, soil organic carbon, soil total phosphorus and soil total nitrogen increased at the beginning and subsequently decreased with an increase in the size of phytogenic hillocks (plant-growing soil). The livestock preference index was elevated in all phases under HG compared to MG. Plant height was significantly decreased under HG compared to MG and NG. Seed production showed no significant differences between HG and NG during the adult to aging phases. The results indicated that S. breviflora-derived hillocks support S. breviflora survival by providing a nutritious soil matrix while aggregating its seeds to ensure population regeneration. Moreover, S. breviflora adapted to HG by reducing height and increasing reproductive input, which induced livestock to intake older plants.

Impacts of livestock grazing on vegetation characteristics and soil chemical properties of alpine meadows in the eastern Qinghai-Tibetan Plateau

ABSTRACTLivestock grazing is one of the significant causes of land degradation. However, the effect of contrasting grazing intensities on soil properties and vegetation in the southeastern Qinghai-Tibetan Plateau (QTP) is poorly understood. We studied the impact of light grazing (LG), moderate grazing (MG), heavy grazing (HG) and no grazing (NG) on vegetation characteristics and the chemical properties of soil samples taken at 0–10 cm, 10–20 cm and 20–30 cm layers from the designated grazing treatments. A total of 42 species representing 32 genera and 16 families were identified. Our result shows that HG significantly reduced total aboveground biomass, vegetation cover, canopy average height, but increased unpalatable aboveground biomass. Soil organic matter declined with increasing grazing intensity and respectively decreased to 64.51%, 65.38% and 82.40% for LG, MG and HG compared to the NG treatment and soil carbon storage exhibited a similar pattern. Soil total nitrogen and phosphorus contents decreased with increasing soil depth, while soil total potassium was not affected by grazing across soil depths. We conclude that 1 yak would have a more severe impact than 3 sheep units on the vegetation community and soil characteristics of alpine meadows in the southeastern QTP.

Differential resistance and resilience of functional groups to livestock grazing maintain ecosystem stability in an alpine steppe on the Qinghai-Tibetan Plateau

Ecosystem stability is one of the main factors maintaining ecosystem functioning and is closely related to temporal variability in productivity. Resistance and resilience reflect tolerance and recovering ability, respectively, of a plant community under perturbation, which are important for maintaining the stability of ecosystems. Generally, heavy grazing reduces the stability of grassland ecosystems, causing grassland degradation. However, how livestock grazing affects ecosystem stability is unclear in alpine steppe ecosystems. We conducted a five-year grazing experiment with Tibetan sheep in a semi-arid alpine steppe on the Qinghai-Tibetan Plateau, China. The experimental treatments included no grazing (NG), light grazing (LG, 2.4 sheep per ha), moderate grazing (MG, 3.6 sheep per ha) and heavy grazing (HG, 6.0 sheep ha). We calculated resistance and resilience of three plant functional groups and ecosystem stability under the three grazing intensities using aboveground primary productivity. The results showed that with increasing grazing intensity, aboveground biomass of each functional group significantly decreased. As grazing intensity increased, the resistance of forbs first increased then decreased. The resilience of graminoids in HG was significantly lower than in LG plots, but the resilience of legumes in HG was higher than in LG and MG plots. The resilience of graminoids was significantly higher than legume and forbs under LG and MG treatments. In HG treatments, resilience of legumes was higher than graminoids and forbs. Ecosystem stability did not change under different grazing intensities, because of dissimilar performance of the resilience and resistance of functional groups. Our results highlight how the differential resistance and resilience of different function groups facilitate the tolerance of alpine steppe to grazing under even a heavy intensity. However, the degradation risk of alpine steppe under heavy grazing still needs to be considered in grassland management due to sharp decreases of productivity.

Grazing alters the phenology of alpine steppe by changing the surface physical environment on the northeast Qinghai-Tibet Plateau, China

The response of vegetation phenology to environmental changes is very complex. We used time-lapse digital cameras to monitor the phenology of an alpine steppe in four winter pastures with different grazing intensities during 2015–2017. The results showed that the beginning of the growing season (BGS) and the growing season length (GSL) of the alpine steppe separately presented advances or prolonged trends with the increase in grazing intensity. There was no regularity in the end of the growing season (EGS) under the change in grazing intensity gradient, but the EGS of the no grazing (NG) plot occurred 24 days ahead of the other plots disturbed by grazing. Different winter grazing intensities obviously had different influences on the surface litter, soil temperature (ST), and soil moisture (SM) during spring but not during autumn. The ST under different grazing intensities played a decisive role in controlling the BGS of alpine steppe, followed by surface litter and SM. The EGS showed a significant correlation with the surface litter in autumn but did not show correlations with ST and SM. These results could further help us understand the phenological mechanisms of the soil surface and guide the scientific management of grazing to adapt to climate change.

Moderate grazing has little effect on global warming potential in the temperate steppes of northern China

Grazing has been reported to significantly affect the flux of three greenhouse gases (GHGs: CO2, CH4 and N2O) in grasslands, but its effect on total global warming potential (GWP) is still unclear. To assess the effect of grazing on GWP, we simultaneously measured the flux of these three GHGs using static chambers in meadow, typical, and desert steppes under no grazing (NG) and summer grazing (SG) conditions during the 2012-14 growing seasons. We aimed to examine the impact of grazing on total GWP across different steppes and to assess the relative contribution of different environmental factors to changes in GWP. Our results showed that total GWP values were almost entirely negative in all steppe environments and displayed high spatio-temporal variability. Net ecosystem exchange was the most important predictor of total GWP in all three steppes, and the positive GWP induced by N2O emission was approximately equal to the negative GWP induced by CH4 uptake. Steppe type and sampling year—but not grazing treatment—were found to affect GWP. Air temperature and precipitation were the major factors driving total GWP change under the no grazing treatment. In contrast, soil temperature, soil moisture, and precipitation explained a significant percentage of variation in total GWP under the summer grazing treatment. Our study suggests that moderate grazing does not change the role of temperate steppe's function in mitigating climate change; however, multi-year GWP data are necessary for extrapolation to a regional scale.