不同放牧压力对植物生物量和绵羊增重的影响

目前,我国草原严重退化,天然草原面积每年减少约6.5×10~5~7×10~6hm~2,同时草原质量不断下降。本研究从不同放牧强度对植物生物量和绵羊增重的影响为出发点,选择新疆类似问题较严重的青河县夏牧场草地和绵羊为研究对象,设计4个不同载畜率水平的放牧强度和1个不放牧的对照实验,对样地内草地生物量和绵羊体重测定和自由式放牧强度对比分析,得出了绵羊体增重达到最佳又使植物群落不受强烈干扰时的放牧强度。通过本研究可知,夏牧场放牧强度为3~6只羊/hm2时,绵羊增重更明显,从而可以达到很好的经济效果,对草地生物量的恢复有一定帮助,能更好的改善草原生态环境。     

基于RS和GIS的赛里木湖流域景观格局动态研究

基于RS和GIS的技术方法,运用景观格局指数对赛里木湖流域近25a来的景观格局变化综合分析。结果表明:1986-2010年,赛里木湖流域疏林地、灌木林地和中覆盖度草地面积增加,有林地、高覆盖度草地面积减小。整体上,景观斑块总数增加,景观破碎化指数、景观类型形状指数和景观多样性指数升高,均匀度指数有所减少。由此可以看出,该区域内由于自然或人为因素干扰所导致的景观斑块类型逐渐变得复杂,景观遭到破坏,土地利用向着多样化和非均匀化的方向发展,景观斑块分布变得很不均匀。     

青南高原“黑土滩”草地群落特征的研究

对高寒草甸及其退化产物—“黑土滩”草地按退化特征划分了6个等级,分别研究了各级草地的群落特征和物种多样性。结果表明:随草地退化程度的加大,群落产量在各级草地内变化不明显,但毒杂草比例有着明显增加的趋势(P<0.01);原生植被嵩草属植物优势度和草地活根量(30cm)趋于明显减少(P<0.01);中度退化的“黑土滩”草地物种多样性指数较大,为3.234。     

近30年库鲁斯台草原退化过程分析

以库鲁斯台草原作为研究区,利用80年代到2014年草原范围内生物量、牲畜量、耕地数量及其用水量等数据,对库鲁斯台草原退化现状及原因进行了分析,结果如下:(1)目前库鲁斯台草原退化严重。草原范围内湿地面积从80年代至2014年减少了85.0%、草地可利用面积减少了36.5%、退化草地面积增加了225%、盐碱化面积增加了233%、草地沙漠化面积增加了2350%。(2)库鲁斯台草原退化主要原因,一是农业用水大幅增加。草原范围内总灌溉面积从80年代至2014年增加了186%、草原内机电井数增加了292%;从80年代到90年代到2000年,额敏河流域总用水量呈先增后减的趋势,从2000年又呈大幅增加的趋势,总用水量从80年代至目前增加了36.11%。二是草地牲畜数量大幅增加,引起草地生物量减少,草原范围内牧业户数从80年代至2014年增加了24%,草原内过冬牲畜量增加了45.6%,草地总产量减少了64.43%。     

伊犁河谷景观格局变化分析

景观生态学是宏观生态研究的一个新的领域.景观动态变化研究,是目前景观生态学中的一个研究热点.基于伊犁河谷2000年、2005年夏季有效时相Landsat TM/ETM 遥感影像资料,综合运用遥感与GIS技术,通过采用分维数,多样性指数,破碎度指数和边界密度等指数,分析了伊犁河谷景观动态变化.研究结果表明:①草地、水域和林地面积大幅度减少,耕地和城乡居民工矿交通用地猛增,城市化进程加快;②伊犁河谷斑块数目增多,景观边缘密度增加,景观破碎度增大,伊犁河谷景观异质性和景观形状的复杂性程度略微提升;③景观基质依然为草地,草地破碎度稍增,草地的多样性和异质性下降;④耕地的斑块数减少而斑块面积增大,破碎化程度降低,耕地的稳定性加强.     

山地荒漠草原不同植物群落关系研究

在群落样方调查的基础上，计算群落物种重要值，确定群落类型。对群落物种重要值采用分割线段模型、对数级数分布、对数正态分布、几何级数分布等4个多度模型进行拟合。结果表明，新疆银穗草一细果苔草群落对数级数拟合结果更好，穗状寒生羊茅一细果苔草群落对数正态分布拟合更好，说明了2个群落结构是对2个样地环境特点与放牧干扰相互作用的响应。新疆银穗草一穗状寒生羊茅群落中新疆银穗草处于极优势地位，占据整个群落的大多数生态空间。拟合检验表明，该山地草地植被物种分布格局较符合随机生态位假说和生态位占领假说，严重的放牧干扰不仅降低了优势物种在群落中的优势程度，使次优势物种及其它物种也没能较好的发育，说明外部非生物环境对群落胁迫程度较大。     

高寒草甸退化草地植物群落结构特征及物种多样性的初步分析

文章以高寒草甸生态系统植物群落样地资料为基础，对不同退化程度植物群落结构及物种多样性特征进行研究分析。结果表明：青藏高原高寒草甸在人为干扰、超载过牧等因素的影响下，草地严重退化，退化草地植物群落物种组成及覆盖度均发生了很大变化，主要表现在物种数急剧减少、植被覆盖度下降、优良牧草比例大幅度减少。就群落物种多样性而言，退化生态系统物种多样性明显低于自然生态系统，并且草地退化越严重，其物种多样性就越低。     

塔里木河下游生态输水的效应

根据塔里木河下游的地下水位、植物调查数据,对比分析了塔里木河下游生态输水后地下水位、生物量、物种多样性变化。结果表明：实施生态输水工程后,地下水位对生态输水的响应显著,地下水位逐渐抬升,下降趋势得以控制。草本植物生物量的变化趋势与每次输水量变化趋势基本一致,即随着输水量的增加草本植物的生物量也相应增加,草本植物生物量对生态输水的响应程度与输水的时间、输水量的多少有密切关系。地下水位埋深上升,物种多样性也呈上升趋势,但二者并不是同步,物种多样性上升趋势滞后于地下水位的上升,这表明地下水位的抬升有利于植物多样性的增加,但是地下水位变化对植物多样性的影响是一个渐变的过程。     

草地生态环境失调主因与控制对策的探讨

草地生态环境失调已成为当今世界面临的一个严重问题。随着草地生态的破坏,制约着草地畜牧业的稳定发展。据大量资料表明,虽然引起草地生态失调的原因是多方面的,如开垦草地,过度放牧、破坏植被等而造成草地退化、水土流失、沙化;但从全局来看,草地超载过牧是导致草地生态失调的根本原因。为此,作者通过对草地生态环境失调成因与危害的分析,提出了维护草地生态平衡的积极对策:①以草定畜,依法管理草地;②落实草场承包责任制,固定草地使用权;③建立完整的草地科学利用体系。逐步制止草地生态恶化,改善草地生态环境。     

柽柳属植物的生物量研究

对中科院吐鲁番沙漠植物园4种柽柳的生物量进行了测定和研究。按“标准木法”分别调查高度，基径和冠幅，按“收割法’测定其各器官的生物量及凋落物。调查数据，应用“相对生长法’健立了估测柽柳整株和各器生物量的回归模型，相关系数均达到显著水平。结果表明：柽柳地上部分生物量分别为；甘蒙柽柳25．85t/hm2，刚毛任柳27.17/hm2，白花柽柳35．46t/hm2，长穗柽柳52．29t/hm2。生物量回归模型分别为W(甘)=0．3643(D2H)1.0001，w(刚)=O．3156（D2H）1.0000，w(白)。0．5839（D2H）0.9999，w（长）。0.5035（D2H）0.9987     

Effects of Grazing Exclusion on Soil Properties and on Ecosystem Carbon and Nitrogen Storage in a Sandy Rangeland of Inner Mongolia, Northern China

The Horqin sandy rangeland of northern China is a seriously desertified region with a fragile ecology. The sandy alluvial and aeolian sediments have a coarse texture and loose structure and are therefore vulnerable to damage caused by grazing animals and wind erosion. We investigated whether grazing exclusion could enhance ecosystem carbon (C) and nitrogen (N) storage and thereby improve overall soil quality. We compared soil properties, C and N storage in biomass (aboveground and below-ground), and the total and light fraction soil organic matter between adjacent areas with continuous grazing and a 12-year grazing exclosure. The soil silt?+?clay content, organic C, total Kjeldahl N, available N and K, and cation-exchange capacity were significantly (P?相似文献   

Storage and dynamics of carbon and nitrogen in soil after grazing exclusion in Leymus chinensis grasslands of northern China

Land-use change can lead to changes in soil carbon (C) and nitrogen (N) storage. This study aimed to determine the impact of long-term grazing exclusion (GE) on soil organic C and total N (TN) storage in the Leymus chinensis grasslands of northern China and to estimate the dynamics of recovery after GE. We investigated the aboveground biomass and soil organic C and TN storage in six contiguous plots along a GE chronosequence comprising free grazing, 3-yr GE, 8-yr GE, 20-yr GE, 24-yr GE, and 28-yr GE. Grazing exclusion for two decades increased the soil C and N storage by 35.7 and 14.6%, respectively, in the 0- to 40-cm soil layer. The aboveground net primary productivity and soil C and N storage were the highest with 24-yr GE and the lowest with free grazing. The storage increased logarithmically with the duration of GE; after an initial rapid increase after the introduction of GE, the storage attained equilibrium after 20 yr. A logarithmic regression analysis revealed 86.8 and 87.1% variation in the soil C storage and 74.2 and 80.7% variation in the soil N storage in the 0- to 10-cm and 0- to 40-cm soil layers, respectively. Based on these results, we suggest that two decades of GE would restore the L. chinensis grasslands from being lightly degraded to a stable productive condition with good soil C and N storage capacity. Our results demonstrated that by implementing GE, the temperate grasslands of northern China could facilitate significant C and N storage on decade scales in the context of mitigating global climate change.     

Impact of Grazing on Plant Species Richness, Plant Biomass, Plant Attribute, and Soil Physical and Hydrological Properties of Vertisol in East African Highlands

Understanding the problems of grazing land in vertisol areas and seeking long-lasting solutions is the central point where mixed crop livestock is the second stay for the majority of the population. In order to understand this, the current study was conducted at two sites, one with 0–4% slope and the other with 4–8% slope at Ginchi watershed, 80 km west of Addis Ababa, Ethiopia. The specific objectives of the study were to quantify changes in plant species richness, biomass, plant cover, and soil physical and hydrological properties. The grazing regimes were: moderate grazing (regulated), heavy grazing (free grazing), and no grazing (closed to any grazing), which was considered the control treatment. The results showed that the biomass yield in nongrazed plots was higher than in the grazed plots. However, the biomass yield in grazed plots improved over the years. Species richness and percentage of dominant species attributes were better in medium grazed plots than the other treatments. Soil compaction was higher in very heavily grazed plots than in nongrazed and medium-grazed plots. In contrast to that, the soil water content and infiltration rate were better in nongrazed plots than in grazed plots. Soil loss in grazed plots decreased with the increase of biomass yields and as the soil was more compacted by livestock trampling during the wet season. Finally since the medium stocking rate is better in species richness and plant attributes, and lies between nongrazed and heavily grazed plots in the rest of the measured parameters, it could be the appropriate stocking rate to practice by the smallholder farmer.     

Consequences of Livestock Grazing on Water Quality and Benthic Algal Biomass in a Canadian Natural Grassland Plateau

The effects of livestock grazing on selected riparian and stream attributes, water chemistry, and algal biomass were investigated over a two-year period using livestock enclosures and by completing stream surveys in the Cypress Hills grassland plateau, Alberta, Canada. Livestock enclosure experiments, partially replicated in three streams, comprised four treatments: (1) early season livestock grazing (June–August), (2) late season livestock grazing (August–September), (3) all season grazing (June–September), and (4) livestock absent controls. Livestock grazing significantly decreased streambank stability, biomass of riparian vegetation, and the extent to which aquatic vegetation covered the stream channels compared with livestock-absent controls. Water quality comparisons indicated significant differences among the four livestock grazing treatments in Battle and Graburn creeks but not in Nine Mile Creek. In Graburn Creek, the concentration of total phosphorus in the all-season livestock grazing treatment was significantly higher than that in the livestock-absent control, and the early season and late season grazing treatments. Concentrations of soluble reactive phosphorus in the all-season livestock grazing treatment also exceeded that in livestock-absent control. In contrast, differences in water quality variables in the remaining 22 comparisons (i.e., 22 of the total 24 comparisons) were minor even when differences were statistically significant. Effects of livestock grazing on algal biomass were variable, and there was no consistent pattern among creeks. At the watershed scale, spatial variation in algal biomass was related (P < 0.05) with concentrations of NO₂ ^? + NO₃ ^? and soluble reactive phosphorus in two of the four study creeks. Nutrient diffusing substrata experiments showed that algal communities were either nitrogen-limited or not limited by nutrients, depending on stream and season.     

Consequences of livestock grazing on water quality and Benthic algal biomass in a Canadian natural grassland plateau

The effects of livestock grazing on selected riparian and stream attributes, water chemistry, and algal biomass were investigated over a two-year period using livestock enclosures and by completing stream surveys in the Cypress Hills grassland plateau, Alberta, Canada. Livestock enclosure experiments, partially replicated in three streams, comprised four treatments: (1) early season livestock grazing (June–August), (2) late season livestock grazing (August–September), (3) all season grazing (June–September), and (4) livestock absent controls. Livestock grazing significantly decreased streambank stability, biomass of riparian vegetation, and the extent to which aquatic vegetation covered the stream channels compared with livestock-absent controls. Water quality comparisons indicated significant differences among the four livestock grazing treatments in Battle and Graburn creeks but not in Nine Mile Creek. In Graburn Creek, the concentration of total phosphorus in the all-season livestock grazing treatment was significantly higher than that in the livestock-absent control, and the early season and late season grazing treatments. Concentrations of soluble reactive phosphorus in the all-season livestock grazing treatment also exceeded that in livestock-absent control. In contrast, differences in water quality variables in the remaining 22 comparisons (i.e., 22 of the total 24 comparisons) were minor even when differences were statistically significant. Effects of livestock grazing on algal biomass were variable, and there was no consistent pattern among creeks. At the watershed scale, spatial variation in algal biomass was related (P < 0.05) with concentrations of NO₂ ⁻ + NO₃ ⁻ and soluble reactive phosphorus in two of the four study creeks. Nutrient diffusing substrata experiments showed that algal communities were either nitrogen-limited or not limited by nutrients, depending on stream and season.     

The Effects of Long-Term Grazing Exclosures on Range Plants in the Central Anatolian Region of Turkey

Over the last fifty years, almost half of the steppe rangeland in the Central Anatolian Region of Turkey (CAR) has been converted to cropland without an equivalent reduction in grazing animals. This shift has led to heavy grazing pressure on rangeland vegetation. A study was initiated in June 2003 using 6 multiscale Modified-Whittaker plots to determine differences in plant composition between areas that have not been grazed in 27 years with neighboring grazed plant communities. A total of 113 plant species were identified in the study area with the ungrazed plots containing 32 plants more than the grazed plots. The major species were Astragalus acicularis, Bromus tomentellus, Festuca valesiaca, Genista albida, Globularia orientalis, Poa bulbosa, and Thymus spyleus ssp rosulans. Grazing impacts on forbs were more pronounced than for grasses and shrubs. Based on Jaccard’s index, there was only a 37% similarity of plant species between the two treatments. Our study led to four generalizations about the current grazing regime and long-term exclosures in the steppe rangeland around the study area: (1) exclosures will increase species richness, (2) heavy grazing may have removed some plant species, (3) complete protection from grazing for a prolonged period of time after a long history of grazing disturbance may not lead to an increase in desirable plant species with a concomitant improvement in range condition, and (4) research needs to be conducted to determine how these rangelands can be improved.     

Simulation of vegetation dynamics and management strategies on south Texas, semi-arid rangeland

In this paper, we describe a model designed to simulate seasonal dynamics of warm and cool season grasses and forbs, as well as the dynamics of woody plant succession through five seral stages, in each of nine different plant communities on the Rob and Bessie Welder Wildlife Refuge. The Welder Wildlife Refuge (WWR) is located in the Gulf Coastal Prairies and Marshes ecoregion of Texas. The model utilizes and integrates data from a wide array of research projects that have occurred in south Texas and WWR. It is designed to investigate the effects of alternative livestock grazing programs and brush control practices, with particular emphasis on prescribed burning, the preferred treatment for brush on the WWR. We evaluated the model by simulating changes in the plant communities under historical (1974-2000) temperature, rainfall, livestock grazing rotation, and brush control regimes, and comparing simulation results to field data on herbaceous biomass and brush canopy cover collected on the WWR over the same period. We then used the model to simulate the effects of 13 alternative management schemes, under each of four weather regimes, over the next 25 years. We found that over the simulation period, years 1974-2000, the model does well in simulating the magnitude and seasonality of herbaceous biomass production and changes in percent brush canopy cover on the WWR. It also does well in simulating the effects of variations in cattle stocking rates, grazing rotation programs, and brush control regimes on plant communities, thus providing insight into the combined effects of temperature, precipitation, cattle stocking rates, grazing rotation programs, and brush control on the overall productivity and state of woody plant succession on the WWR. Simulation of alternative management schemes suggests that brush canopy removal differs little between summer and winter prescribed burn treatments when precipitation remains near the long-term average, but during periods of low precipitation canopy removal is greater under winter prescribed burning. The model provides a useful tool to assist refuge personnel with developing long-term brush management and livestock grazing strategies.     

Response of Organic and Inorganic Carbon and Nitrogen to Long-Term Grazing of the Shortgrass Steppe

We investigated the influence of long-term (56 years) grazing on organic and inorganic carbon (C) and nitrogen (N) contents of the plant–soil system (to 90 cm depth) in shortgrass steppe of northeastern Colorado. Grazing treatments included continuous season-long (May–October) grazing by yearling heifers at heavy (60–75% utilization) and light (20–35% utilization) stocking rates, and nongrazed exclosures. The heavy stocking rate resulted in a plant community that was dominated (75% of biomass production) by the C₄ grass blue grama (Bouteloua gracilis), whereas excluding livestock grazing increased the production of C₃ grasses and prickly pear cactus (Opuntia polycantha). Soil organic C (SOC) and organic N were not significantly different between the light grazing and nongrazed treatments, whereas the heavy grazing treatment was 7.5 Mg ha^–1 higher in SOC than the nongrazed treatment. Lower ratios of net mineralized N to total organic N in both grazed compared to nongrazed treatments suggest that long-term grazing decreased the readily mineralizable fraction of soil organic matter. Heavy grazing affected soil inorganic C (SIC) more than the SOC. The heavy grazing treatment was 23.8 Mg ha^–1 higher in total soil C (0–90 cm) than the nongrazed treatment, with 68% (16.3 Mg ha^–1) attributable to higher SIC, and 32% (7.5 Mg ha^–1) to higher SOC. These results emphasize the importance in semiarid and arid ecosystems of including inorganic C in assessments of the mass and distribution of plant–soil C and in evaluations of the impacts of grazing management on C sequestration.     

Relationship Between Pastoralists’ Evaluation of Rangeland State and Vegetation Threshold Changes in Mongolian Rangelands

Applying the threshold concept to rangeland management is an important challenge in semi-arid and arid regions. Threshold recognition and prediction is necessary to enable local pastoralists to prevent the occurrence of an undesirable state that would result from unsustainable grazing pressure, but this requires a better understanding of the pastoralists’ perception of vegetation threshold changes. We estimated plant species cover in survey plots along grazing gradients in steppe and desert-steppe areas of Mongolia. We also conducted interviews with local pastoralists and asked them to evaluate whether the plots were suitable for grazing. Floristic composition changed nonlinearly along the grazing gradient in both the desert-steppe and steppe areas. Pastoralists observed the floristic composition changes along the grazing gradients, but their evaluations of grazing suitability did not always decrease along the grazing gradients, both of which included areas in a post-threshold state. These results indicated that local pastoralists and scientists may have different perceptions of vegetation states, even though both of groups used plant species and coverage as indicators in their evaluations. Therefore, in future studies of rangeland management, researchers and pastoralists should exchange their knowledge and perceptions to successfully apply the threshold concept to rangeland management.     

Phytoextraction of heavy metals by willows growing in biosolids under field conditions

Biosolids produced by sewage treatment facilities can exceed guideline thresholds for contaminant elements. Phytoextraction is one technique with the potential to reduce these elements allowing reuse of the biosolids as a soil amendment. In this field trial, cuttings of seven species/cultivars of Salix(willows) were planted directly into soil and into biosolids to identify their suitability for decontaminating biosolids. Trees were irrigated and harvested each year for three consecutive years. Harvested biomass was weighed and analyzed for the contaminant elements: As, Cd, Cu, Cr, Hg, Pb, Ni, and Zn. All Salix cultivars, except S. chilensis, growing in soils produced 10 to 20 t ha(-1) of biomass, whereas most Salix cultivars growing in biosolids produced significantly less biomass (<6 t ha(-1)). Salix matsudana (30 t ha(-1)) and S. × reichardtii A. Kerner (18 t ha(-1)) had similar aboveground biomass production in both soil and biosolids. These were also the most successful cultivars in extracting metals from biosolids, driven by superior biomass increases and not high tissue concentrations. The willows were effectual in extracting the most soluble/exchangeable metals (Cd, 0.18; Ni, 0.40; and Zn, 11.66 kg ha(-1)), whereas Cr and Cu were extracted to a lesser degree (0.02 and 0.11 kg ha(-1)). Low bioavailable elements, As, Hg, and Pb, were not detectable in any of the aboveground biomass of the willows.