Effects of rotational and continuous grazing on herbage quality,feed intake and performance of sheep on a semi-arid grassland steppe

Compared to continuous grazing (CG), rotational grazing (RG) increases herbage production and thereby the resilience of grasslands to intensive grazing. Results on feed intake and animal performance, however, are contradictory. Hence, the objective of the study was to determine the effects of RG and CG on herbage mass, digestibility of ingested organic matter (dOM), organic matter intake (OMI) and live weight gain (LWG) of sheep in the Inner Mongolian steppe, China. During June–September 2005–2008, two 2-ha plots were used for each grazing system. In RG, plots were divided into four 0.5-ha paddocks that were grazed for 10 days each at a moderate stocking rate. Instead, CG sheep grazed the whole plots throughout the entire grazing season. At the beginning of every month, dOM was estimated from faecal crude protein concentration. Faeces excretion was determined using titanium dioxide in six sheep per plot. The animals were weighed every month to determine their LWG. Across the years, herbage mass did not differ between systems (p = 0.820). However, dOM, OMI and LWG were lower in RG than in CG (p ≤ 0.005). Thus, our study showed that RG does not improve herbage growth, feed intake and performance of sheep and suggests that stocking rates rather than management system determine the ecological sustainability of pastoral livestock systems in semi-arid environments.     

Forage nutritional characteristics and yield dynamics in a grazed semiarid steppe ecosystem of Inner Mongolia,China

In the steppe of Inner Mongolia, forage is the only source of feed for sheep. The forage intake of sheep can be characterized in both quantity and quality terms, which are determined by environmental and anthropogenic factors and grazing has a strong effect on steppe productivity and the grassland ecosystem. Evaluation of forage quality and quantity is therefore of critical importance. The effects of grazing intensity, interannual variability effects, and species composition on aboveground net primary productivity (ANPP) and forage nutritional characteristics were investigated in a controlled grazing experiment along a gradient of 7 grazing intensities (from non-grazed to very heavily grazed) over six years (2005–2010) on typical steppe in Inner Mongolia. Forage nutritional characteristics were defined by the nutritional value (concentrations of crude protein (CP), cellulase digestible organic matter (CDOM), metabolizable energy (ME) and neutral detergent fibre (NDF)) and the nutritional yield. The forage nutritional yield is a function of ANPP and the forage nutritional value. Forage nutritional value increased but ANPP and nutritional yields decreased with increasing grazing intensity. The inter-annual variation of ANPP, forage nutritional value and yield were weakly linked to the inter-annual variability of precipitation. However, ANPP and nutritional value also varied during the growing season, depending on the seasonal distribution of precipitation and temperature, which influence forage digestibility (CDOM) and metabolizable energy (ME), with higher CDOM and ME under high seasonal precipitation and low seasonal mean temperature. Forage nutritional value and yield, as well as ANPP, were predominantly determined by the dominant species rather than by species diversity. The results suggest that forage nutritional yield in the Inner Mongolian steppe is predominantly determined by the ANPP and only to a minor extent by forage nutritional value, and is predominantly determined by the dominant species and only to a minor extent by species diversity. Therefore, herbage productivity seems to be the most limiting factor in managing this steppe ecosystem as a feeding resource for livestock and to be the best ecological and environmental indicator for grassland management practices.     

The pattern between nitrogen mineralization and grazing intensities in an Inner Mongolian typical steppe

Ungulate grazing is known to play a crucial role in regulating energy flow and nutrient cycling in grassland ecosystems. However, previous studies of the effect of grazing on soil N dynamics have showed controversial results. Some studies indicate that grazing stimulates N mineralization while others report that grazing suppresses N mineralization. In order to reconcile these contrasting results, we investigated the response pattern of nitrogen transformation to multiple grazing intensities in an Inner Mongolian steppe. In our study, we measured net nitrogen mineralization rates and nitrification rates during a whole growing season in a 17-year field experiment that had five grazing intensities (0.00, 1.33, 2.67, 4.00 and 5.33 sheep ha⁻¹). Primarily because of changes in temperature and moisture conditions, net N mineralization rates varied substantially during the growing season with higher values occurring in late July. No consistent differences in net N mineralization rates were observed between grazing intensity treatments at the monthly time scale. Compared to mineralization rates, net nitrification rates were generally low with slightly higher values occurring in late July and late August. Ungulate grazing stimulated the cumulative net N transformations (mineralization, nitrification and ammonification) at the annual time scale, and the most stimulation occurred at a moderate grazing intensity of 4.00 sheep ha⁻¹, whereas the highest grazing intensity of 5.33 sheep ha⁻¹ and the lighter grazing intensity of 1.33 sheep ha⁻¹ stimulated less. The general response of net N mineralization to grazing intensity gradient is roughly in the form of a normal distribution at the annual time scale. Our study demonstrated that grazing intensity in concert with soil moisture and temperature conditions imposed significant controls on soil N transformation and availability in this Inner Mongolian steppe.     

地植物多样性间的关系

用显微技术法分别在放牧率为 1 .33,4 .0 0和 6.67只 / hm2下对内蒙古细毛羊的食性进行了研究。结果表明 ,随着放牧率的增大 ,草场的植物种类组成及其相对比例发生了明显的变化。由于不同牧草的可利用性不同 ,其食性选择也发生了明显的变化。在重牧条件下 ,原先为随意采食的冷蒿和厌食的寸草苔则升级为“喜食”的植物 ,星毛委陵菜的选择性指数也有较大提高 ;且星毛委陵菜成为主要的食物资源 ,占全部食物的 80 %以上。这说明放牧率的增大和绵羊选择性的采食是草场植物种类组成发生变化的主要原因之一。食物的选择性主要与草地牧草的相对生物量、高度和频度显著相关 ;当草地植物多样性指数较高时 ,放牧绵羊的食物选择性较大。不同放牧率条件下 ,在以冷蒿和小禾草为主的退化草原上 ,草地植物多样性指数随放牧率的增大而显著降低 ,但食物多样性指数以放牧率 4 .0 0只 / hm2 的处理最高。     

Strategies for the avoidance of faeces by grazing sheep

Experiments were conducted to investigate which environmental cues were used by sheep when discriminating against patches of pasture contaminated with faeces. The influence of the spatial distribution of contaminated patches and the parasite infection status of sheep on avoidance of contaminated patches and ingestion of parasite larvae was also investigated. In experiment 1, sheep infected with the parasite Ostertagia circumcincta were given the opportunity to graze in uncontaminated or aggregated contaminated patches. Patch contamination comprised of either faeces from sheep infected with O. circumcincta larvae, faeces from uninfected sheep, or O. circumcincta larvae only. Infected sheep discriminated against faeces from parasite-infected animals and faeces from uninfected animals equally. Sheep did not discriminate against patches contaminated with parasite larvae only. In experiment 2, sheep infected with O. circumcincta and uninfected sheep grazed experimental plots with differing spatial patterns of faecal-contaminated patches, allowing animals the opportunity to forage in contaminated or uncontaminated patches of herbage. Plots were also grazed by infected and uninfected animals that were fistulated at the oesophagus to enable the collection of ingested herbage. Sheep spent a greater proportion of their time foraging in uncontaminated patches than in contaminated patches. Where patches were highly aggregated, infected animals spent a greater proportion of total grazing time in uncontaminated patches than did uninfected animals, and grazed uncontaminated patches for longer on each sampling occasion. On grazing plots where all patches were contaminated, the difference between the numbers of larvae isolated from pasture herbage and ingested herbage was greatest for infected animals. In this situation, infected animals avoided parasites most. On grazing plots consisting of both contaminated and uncontaminated patches, the difference between the numbers of larvae isolated from pasture herbage and ingested herbage was greatest for uninfected animals. In this situation, uninfected animals were most effective at parasite avoidance as they consumed fewer parasite larvae relative to what was available on pasture.     

不同放牧率下绵羊的食性及食物多样性与草地植物多样性间的关系

用显微技术法分别在放牧率为1.33．4．00和6．67只／hm^2下对内蒙古细毛羊的食性进行了研究。结果表明,随着放牧率的增大,草场的植物种类组成及其相对比例发生了明显的变化。由于不同牧草的可利用性不同,其食性选择也发生了明显的变化。在重牧条件下,原先为随意采食的冷蒿和厌食的寸草苔则升级为“喜食”的植物,星毛委陵菜的选择性指数也有较大提高;且星毛委陵菜成为主要的食物资源,占全部食物的80%以上,这说明放牧率的增大和绵羊选择性的采食是草场植物种类组成发生变化的主要原因之一。食物的选择性主要与草地牧草的相对生物量、高度和频度显著相关;当草地植物多样性指数较高时,放牧绵羊的食物选择性较大。不同放牧率条件下,在以冷蒿和小禾草为主的退化草原上．草地植物多样性指数随放牧率的增大而显著降低,但食物多样性指数以放牧率4．00只／hm^2的处理最高。     

Effects of livestock grazing intensity on soil biota in a semiarid steppe of Inner Mongolia

Intensive livestock is known to significantly affect soil physical and chemical parameters in steppe ecosystems. However, the effects on soil biological parameters still remain unknown. We hypothesized that intensive grazing would significantly decrease the size and diversity of soil biota due to deterioration of the soil environment and reduction in vegetation cover, while the adapted grazing intensity would improve the biological parameters. Soil samples were collected from five sites with different grazing intensities and history in a semiarid steppe of Inner Mongolia in August 2005. Two sites were long-term ungrazed since 1979 (UG79) and 1999 (UG99), one had been moderately grazed in winter (WG), one continuously grazed moderately (CG) and one long-term site was heavily grazed (HG). Soil microbial biomass carbon (C), basal respiration (BR), catabolic diversity of soil microbial communities, protozoa and nematodes abundance were measured. Soil physicochemical variables were also measured to establish the relationships between soil biological parameters and key soil physical and chemical properties. Soil microbial biomass C, BR, biomass specific respiration (qCO₂) and soil protozoa abundance were significantly lower at the HG site compared to the UG79 site, but no clear differences were found in the other sites. However, soil nematodes abundance increased with increasing grazing intensity, and the abundance of soil amoeba were greater in CG than in the other sites. Principal component analysis (PCA) of Biolog data revealed large differences in catabolic capacity of soil microbial communities between UG79, HG and UG99, WG, CG. However, Shannon??s diversity index did not indicate marked effects of grazing intensity on substrate catabolic community structure. In conclusion, heavy grazing negatively affected soil microbial biomass, activity and protozoan abundance, but positively influenced soil nematodes abundance and did not affect soil microbial catabolic diversity. Based on these results, CG may provide an appropriate grazing intensity to be used in the long term in the semiarid steppe of Inner Mongolia.     

不同利用方式和载畜率对内蒙古典型草原群落初级生产力和植物补偿性生长的影响

基于2005年6月开始的放牧控制实验, 研究了不同草地利用方式和放牧强度对内蒙古典型羊草(Leymus chinensis)草原群落初级生产力和补偿性生长的影响。草地利用方式包括: 传统放牧、传统割草和放牧与割草轮换利用(混合利用)。结果表明: 传统放牧和混合利用方式下, 羊草群落地上生物量均随放牧强度增加逐渐降低。高载畜率下, 羊草群落地上净初级生产力表现为: 混合利用>传统割草>传统放牧, 说明混合利用方式优于传统放牧和传统割草利用方式; 而低载畜率则有利于草原的可持续利用和植物的补偿性生长。这一实验结果在一定程度上验证了放牧优化假说。在不同利用方式、地形因素的影响和采用不同的群落净生长量计算方法时, 随着放牧强度的变化, 等补偿、超补偿和欠补偿效应都可能出现。在低载畜率下, 群落大多表现出等补偿生长, 在高载畜率下, 群落大多表现出欠补偿生长。植物群落的补偿性生长与载畜率的关系可以用开口向下的二次函数或者斜率为负的线性函数模拟。说明随着载畜率的增加, 一些系统表现为欠补偿生长, 而另一些系统则表现为超补偿生长, 这可能与植物群落组成、地形部位(平地、坡地)和载畜率以及净生长量的计算方法有关。     

放牧对内蒙古典型草原粪金龟子群落的影响

为阐明放牧对粪金龟子群落的影响, 于2004年5-9月, 选择内蒙古典型草原不同放牧强度 (无放牧、 适度放牧和过度放牧) 草地为样地, 采用诱捕法采集粪金龟子标本, 分析了放牧对粪金龟子群落的影响。结果表明： 共捕获粪金龟子60 839头, 隶属于3科5属24种。放牧影响下, 粪金龟子群落个体数、 种数和生物量均发生显著变化, 不同粪金龟子对放牧的敏感性不同, 并具有明显的季节特征。Pearson相关分析表明, 春季粪金龟子群落个体数、 生物量、 种数以及符号蜉金龟Aphodius comma和马粪蜉金龟Aphodius subterraneus个体数与放牧强度提高之间存在显著负相关关系; 夏季粪金龟子群落种数和叉角粪金龟Ceratophyus polyceros个体数与放牧强度提高也呈显著负相关; 秋季粪金龟子群落生物量和种数以及费氏粪金龟Ceratophyus fischeri、 墨侧裸蜣螂Gymnopleurus mopsus和小驼嗡蜣螂Onthophagus gibbulus个体数与放牧强度提高之间存在显著正相关关系。依据体长、 体重和行为特征, 将粪金龟子划分为4个功能群, 放牧对体型较小的功能群Ⅲ和Ⅳ的影响较显著。指示值计算结果表明, 费氏粪金龟、 毛蜉金龟Aphodius scofa和马粪蜉金龟可以作为不同放牧强度草地的特征指示种。     

Grassland responses to grazing: effects of grazing intensity and management system in an Inner Mongolian steppe ecosystem

The major aims of this study were, firstly, to analyse the grazing-induced steppe degradation process and, secondly, to identify an efficient and sustainable grazing management system for the widely degraded Inner Mongolian typical steppe ecosystem. From 2005?C2008 a grazing experiment was conducted to compare two grazing management systems, the Mixed System (MS) and the Traditional System (TS), along a gradient of seven grazing intensities, i.e. ungrazed (GI0), very-light (GI1), light (GI2), light-moderate (GI3), moderate (GI4), heavy (GI5), and very-heavy (GI6). Each grazing intensity treatment was considered a production unit comprising two adjacent plots, one for hay-making (single-cut system) and one for grazing. Hay-making and grazing alternated annually in the MS, while in the TS the same plots were used either for hay-making or for grazing. Effects of management system, grazing intensity, and year on end-of-season standing biomass (ESSB), aboveground net primary production (ANPP), relative difference in ANPP between 2005 and 2008 (ANPP_Diff), relative growth rate (RGR), and sward characteristics (litter accumulation, soil coverage) were analysed. Litter accumulation of production units was affected by grazing intensity (P?<?0.001) and decreased from GI0 to GI6 by 83%. Correspondingly, soil coverage decreased (P?<?0.001) from GI0 to GI6 by 43%, indicating an increased vulnerability to soil erosion. We found varying compensatory growth responses to grazing intensity among years, probably because of temporal variability in precipitation. The ability of plants to partially compensate for grazing damage was enhanced in years of greater seasonal precipitation. The ANPP of production units was negatively affected by grazing intensity and decreased from GI0 to GI6 by 37, 30, and 55% in 2006 (P?<?0.01), 2007 (P?<?0.05), and 2008 (P?<?0.001), respectively. The effect of management system × grazing intensity interaction on ANPP (P?<?0.05) and ANPP_Diff (P?<?0.05) suggested greater grazing resilience of the MS as compared to the TS at GI3 to GI6.     

Spontaneous steppe restoration on abandoned cropland in Kazakhstan: grazing affects successional pathways

After the collapse of the Soviet Union in 1991, 12 million ha of cropland were abandoned in the steppe zone of Kazakhstan. At the same time livestock numbers crashed, leaving large areas of steppe without any grazing. We aimed to investigate, to which degree spontaneous succession on former cropland leads to the restoration of native steppe vegetation, and how this process is influenced by changing grazing patterns. We recorded biomass and vegetation characteristics as well as local soil and landscape variables in 151 quadrats of 100 m², covering 89 plots on former cropland abandoned in the early 1990s and 62 reference plots of near-natural steppe grassland that was never ploughed. About half of the plots of each category were located in a remote region where grazing has been absent for ca. 20 years, whereas the other half was located in a region with moderate livestock grazing. While there were no differences in the diversity, structure and plant life form composition of currently grazed and un-grazed near-natural steppe grasslands, corresponding successional plots on abandoned arable land exhibited significant differences. Grazed plots on former fields showed higher species richness and a higher cover of dwarf shrubs (mostly Artemisia spec.), ruderals and perennial herbs. At the same time, immigration of typical steppe species was much more successful. Contrary, in the absence of any grazing we found species-poor swards dominated by Stipa lessingiana and Leymus ramosus exhibiting an increasing frequency of wildfires due to litter accumulation. After 15–20 years, secondary steppe grasslands still differed substantially from their near-natural references. Our results suggest that grazing is mandatory to fully restore the original near-natural steppe vegetation and the underlying processes of pyric herbivory.     

Responses of soil respiration to simulated precipitation pulses in semiarid steppe under different grazing regimes

Aims Precipitation pulses and different land use practices (such as grazing) play important roles in regulating soil respiration and carbon balance of semiarid steppe ecosystems in Inner Mongolia. However, the interactive effects of grazing and rain event magnitude on soil respiration of steppe ecosystems are still unknown. We conducted a manipulative experiment with simulated precipitation pulses in Inner Mongolia steppe to study the possible responses of soil respiration to different precipitation pulse sizes and to examine how grazing may affect the responses of soil respiration to precipitation pulses.Methods Six water treatments with different precipitation pulse sizes (0, 5, 10, 25, 50 and 100 mm) were conducted in the ungrazed and grazed sites, respectively. Variation patterns of soil respiration of each treatment were determined continuously after the water addition treatments.Important findings Rapid and substantial increases in soil respiration occurred 1 day after the water treatments in both sites, and the magnitude and duration of the increase in soil respiration depended on pulse size. Significantly positive relationships between the soil respiration and soil moisture in both sites suggested that soil moisture was the most important factor responsible for soil respiration rate during rain pulse events. The ungrazed site maintained significantly higher soil moisture for a longer time, which was the reason that the soil respiration in the ungrazed site was maintained relatively higher rate and longer period than that in the grazed site after a rain event. The significant exponential relationship between soil temperature and soil respiration was found only in the plots with the high water addition treatments (50 and 100 mm). Lower capacity of soil water holding and lower temperature sensitivity of soil respiration in the grazed site indicated that degraded steppe due to grazing might release less CO₂ to the atmosphere through soil respiration under future precipitation and temperature scenarios.     

不同刈牧强度对冷蒿生长与资源分配的影响

利用野外实验与盆栽实验,对不同刈牧强度下冷蒿生长与资源分配影响的研究结果表明,按比例刈割冷篙的再生生长大于留茬高度刈割,在生长季前期,不刈割冷蒿净生长高于刈割处理,而进入生长季中后期(8月中旬以后),轻度刈割净生长高于不刈割处理,冷篙种群生物量分配的总体格局是根>叶>茎,刈牧明显影响冷蒿生物量分配格局,尤其是叶和花的分配,3／4刈割或留茬4cm刈割叶生物量分配显著高于其它各处理,而花的生物量及其分配显著低于其它处理,根、茎生物量分配各处理间差异不显著．冷蒿有性生殖分配随刈牧强度的增加而降低,繁殖方式发生了改变,优先将光合产物分配给再生茎以及繁殖方式转向营养繁殖,通过克隆生长维持和扩大种群是冷蒿对强度放牧的生态适应对策。     

Diet selection of sheep shifted from quality to quantity characteristics of forages as sward availability decreased

Understanding the dynamic inter-relationship between grazing animals and the pasture sward is critical for sustainable grazing management. A field study was conducted to investigate the relationships between the quantity and quality characteristics of forages and diet selection of 30-kg Mongolian ewes in different seasons in Bromus inermis improved meadow steppe. Using a residual herbage mass method (1 000 kg/ha in spring, 800 kg/ha in summer and 600 kg/ha in autumn) to adjust stocking rate, three seasonal rest grazing strategies (spring rest, summer rest and autumn rest) combined with continuous grazing were studied. In each season, diet selection of sheep, quantified by diet composition and selectivity index, was estimated using a plant wax marker technique. Quantity (dry weight proportion, coverage, frequency, density and height) and quality (CP, NDF, ADF and DM digestibility) characteristics of forages consumed by sheep were determined simultaneously. Our results showed that in spring with the highest sward availability (herbage mass), diet selection of sheep could be predicted by the positive linear relationship between quality characteristics of forages and their selectivity index. In summer, the diet selection could be predicted by both positive linear relationship between quality characteristics and selectivity index, and the relationship between quantity characteristics and diet composition. While in autumn with the lowest sward availability, it could be predicted by the positive linear relationship between quantity characteristics and diet composition. During the whole grazing season, the diet composition of B. inermis (40.4%) and Leymus chinensis (35.1%) were larger than that of Potentilla bifurca (9.5%) and Carex (15.1%) and the selectivity index of P. bifurca was the highest (0.62), followed by Carex (0.17) and B. inermis (0.05), and L. chinensis (?0.29) was the lowest. The two parameters of diet selection above were positively related to their quantity and quality characteristics, respectively. These results suggested that the influence of quality characteristics on diet selection of sheep decreased gradually as a result of the decline in sward availability, while the influence of quantity characteristics increased. This study provides a comprehensive understanding of diet selection of sheep examining the trade-offs between quantity and quality characteristics of forages. The knowledge of diet selection of sheep and the corresponding prediction regressions acquired in this study could give the basis for designing appropriate grazing management strategies.     

Impact of grazing regime on a Mongolian forest steppe

Question: What is the impact of grazing regime on plant species abundance, plant growth form, plant productivity and plant nutrient concentrations in a forest steppe? Location: Hustai National Park in the forest steppe region of Mongolia. Methods: On the Stipa steppe we applied three different grazing regimes by using; (1) one type of exclosure which excluded grazing by large mammalian herbivores, mainly takh (Przewalski horse), (2) another type of exclosure that excluded both large and small (Siberian marmots) mammalian herbivores, and (3) control plots which were freely grazed. We measured species frequencies, tiller densities, plant biomass and nitrogen concentrations of the vegetation. Results: Exclusion from grazing by takh and marmots significantly increased plant standing crop, but marmot grazing and full grazing did not show significant differences. Protection from grazing decreased forage quality, shown by a lower N-concentration of the standing crop. However, this was solely the result of the lower live-dead ratio of the vegetation. The frequency of the rhizomatous Leymus chinensis decreased under reduced grazing, as did the frequency of the total of rhizomatous species. The frequency of Stipa krylovii increased under reduced grazing, as did its basal areas, tiller density and tussock height. Conclusion: Reduced grazing leads to a lower abundance of rhizomatous species and an increase in tussock species.     

退化草原冷蒿群落13年不同放牧强度后的植物多样性

放牧过程通过家畜的啃食、践踏干扰草原环境,使草原的物种组成发生变化,植物种群的优势地位发生更替。对退化草原中的冷蒿群落在经历13a不同放牧强度——无牧（0．00只羊,hm^2）、轻牧（1．33只羊／hm^2）、中牧（4．00只羊／hm^2）、重牧（6．67只羊,hm^2）的围栏放牧后的植物群落多样性进行研究,结果表明：经过13a的演替变化,（1）无牧处理下植被密度显著低于其它3个放牧处理下的植被密度,而其它3个放牧处理之间的植被密度差异不显著;（2）无牧处理下羊草成为群落的优势种,轻牧和中牧处理下冷蒿依然是群落的优势种。这3种处理下寸草苔的种群密度最大;重牧处理下优势种变为星毛委陵菜,并且其种群密度最大;随着放牧强度增加,不同放牧退化阶段指示植物的种群密度的变化趋势是：冷蒿为先增大后减小,而星毛委陵菜为先急剧增大,然后平缓增大,最后再急剧增大;（3）植物多样性和均匀度指数在中牧处理下最大,在无牧处理下最小,说明中牧处理下群落的多样性最高,无牧处理下群落的多样性最小。而优势度指数正相反。植物群落结构和多样性的变化主要是由放牧家畜选择性采食、不同植物对放牧响应的不同策略、植物种间的竞争、动植物协同进化以及由放牧改变的土壤理化性质等因素综合决定的。此研究有助于进一步认识退化草原在继续放牧干扰下的演替规律以及为退化草原的保护和恢复提供理论依据。     

The impact of grazing management on Orthoptera abundance varies over the season in Mediterranean steppe-like grassland

As semi-natural grassland has a high level of biological diversity, understanding the effects of grazing and its variation over time is important in order to identify sustainable grazing practices. We measured temporal variation in Orthoptera abundance and spatial vegetation structure during seasonal grazing in an extensive sheep-farming system. We studied five grazed pasture areas (pre-grazing and post-grazing) and two adjacent ungrazed grasslands. We recorded the total abundance of Orthoptera and described the vegetation structure of 175 replicate plots (25 per pasture/grassland) during six field sampling sessions. We demonstrated that the impact of grazing on Orthoptera abundance is species-specific and greatly varies over the grazing season. The decrease of phytovolume is significant after 4–7 weeks of sheep grazing. Total Orthoptera abundance was higher in pre-grazed plots than in ungrazed plots, and higher in ungrazed plots than in post-grazed plots. These differences were particularly high during the peak of adult abundance. No difference in species richness was observed between grazing intensities. Total Orthoptera abundance positively correlated to phytovolume only when grazing pressure was high. However, the relationship between abundance and phytovolume differed between species. Extensive grazing by sheep tends to homogenize spatial vegetation structure and to temporarily reduce total Orthoptera abundance at pasture scale. However, rotational grazing allows spatial and temporal heterogeneity in vegetation structure to be maintained at farm scale, heterogeneity that is beneficial for Orthoptera. In contrast, absence of grazing has a negative impact on Orthoptera abundance as it favours the accumulation of litter, which is detrimental for a high proportion of xerothermophilic Orthoptera associated with bare ground and short vegetation.     

短期围栏封育后再利用对草地植物群落的影响

短期围栏封育后再适度利用是当前生态治理工程中使用较多的草地恢复措施,明确其实施效果对后续生态工程的优化调整具有重要意义。目前关于围栏封育和放牧对草地影响的研究较为丰富,但鲜有研究探讨短期围栏封育后再利用对草地的长期影响。以京津风沙源工程2002—2005年间在锡林郭勒地区实施的围栏封育地块为研究对象,通过配对采样调查和遥感数据分析,开展围栏封育期和重新放牧利用期连续近20年的草地植物群落变化研究。结果表明,草地植被高度、覆盖度和地上生物量在3年的围栏封育期内迅速增加,重新放牧利用后这些指标虽有所下降但仍显著高于持续放牧草地,并最终达到稳定状态。2002—2020年间短期围栏封育后再利用地块的植被覆盖度(FVC)整体上呈不显著的增加趋势、净初级生产力(NPP)呈显著增加趋势,FVC和NPP呈增加趋势的地块比例在温性草甸草原区、温性荒漠草原区和温性草原区依次减少。总的来说,3年的围栏封育后再放牧利用对草地植物群落具有一定的恢复作用。     

围栏封育和自由放牧对克氏针茅草原植被空间异质性的影响

群落组成结构的异质性是群落动态的主要属性。本研究采用样线、样方调查方法,基于物种频度与幂函数法则,分析了内蒙古克氏针茅草原围栏封育和自由放牧条件下群落物种结构与空间异质性的变化。结果表明:在围栏外和围栏内不同利用方式下,物种均呈现集中分布;从水分生态型、生活型、生育型、种子传播型和植物科属等不同功能群类别来看,旱生植物和中旱生植物广泛分布,生活型以多年生草本植物为主,依靠重力传播种子的植物占有相对较大的比例,达到60%以上,禾本科、百合科、菊科和豆科等适牧植物具有相对优势;在围栏保护状态下,物种多样性增加,群落异质性降低,放牧退化草原开始向群落状况良好的草原类型演替。     

放牧强度对内蒙古荒漠草原土壤有机碳及其空间异质性的影响

放牧是内蒙古荒漠草原主要利用方式之一,研究不同放牧强度下土壤有机碳分布规律对退化草原恢复以及推广精准放牧技术具有重要的指导意义。基于不同放牧强度长期放牧样地（0、0.93、1.82、2.71羊单位hm^-2（a/2）^-1）,采用高样本数量的取样设计并结合地统计学分析方法,研究荒漠草原土壤有机碳及其空间异质性。结果表明：中度放牧会显著降低0-30 cm土层全氮含量（P<0.05）,全磷含量随放牧强度增强出现先降低后升高趋势;放牧样地土壤有机碳含量均显著低于对照样地（P<0.05）,不同放牧强度处理土壤有机碳含量没有显著差异;土壤有机碳密度受放牧影响在0-20 cm土层出现显著下降（P<0.05）,变化趋势同有机碳含量相似,碳氮比在重度放牧区0-10 cm土层显著降低（P<0.05）。土壤有机碳空间异质性和异质性斑块的破碎程度随放牧强度增加而增大;土壤有机碳含量与海拔高度在对照、轻度放牧和中度放牧区均呈极显著负相关（P<0.01）,在重度放牧区土壤有机碳含量和海拔无显著相关性;土壤有机碳含量与土壤全氮、全磷含量均呈极显著正相关（P<0.01）。综上所述,放牧降低土壤有机碳含量,提高土壤有机碳空间异质性,土壤有机碳含量的空间变异受海拔和土壤养分含量等因素的共同影响。