Unravelling the rationale of 'overgrazing' and stocking rates in the beef production systems of Central Brazil using a bi-criteria compromise programming model

In Central Brazil, the long-term sustainability of beef cattle systems is under threat over vast tracts of farming areas, as more than half of the 50 million hectares of sown pastures are suffering from degradation. Overgrazing practised to maintain high stocking rates is regarded as one of the main causes. High stocking rates are deliberate and crucial decisions taken by the farmers, which appear paradoxical, even irrational given the state of knowledge regarding the consequences of overgrazing. The phenomenon however appears inextricably linked with the objectives that farmers hold. In this research those objectives were elicited first and from their ranking two, ‘asset value of cattle (representing cattle ownership)' and ‘present value of economic returns', were chosen to develop an original bi-criteria Compromise Programming model to test various hypotheses postulated to explain the overgrazing behaviour. As part of the model a pasture productivity index is derived to estimate the pasture recovery cost. Different scenarios based on farmers' attitudes towards overgrazing, pasture costs and capital availability were analysed. The results of the model runs show that benefits from holding more cattle can outweigh the increased pasture recovery and maintenance costs. This result undermines the hypothesis that farmers practise overgrazing because they are unaware or uncaring about overgrazing costs. An appropriate approach to the problem of pasture degradation requires information on the economics, and its interplay with farmers' objectives, for a wide range of pasture recovery and maintenance methods. Seen within the context of farmers' objectives, some level of overgrazing appears rational. Advocacy of the simple ‘no overgrazing' rule is an insufficient strategy to maintain the long-term sustainability of the beef production systems in Central Brazil.

Unravelling the rationale of 'overgrazing' and stocking rates in the beef production systems of Central Brazil using a bi-criteria compromise programming model

In Central Brazil, the long-term, sustainability of beef cattle systems is under threat over vast tracts of farming areas, as more than half of the 50 million hectares of sown pastures are suffering from. degradation. Overgrazing practised to maintain high stocking rates is regarded as one of the main causes. High stocking rates are deliberate and crucial decisions taken by the farmers, which appear paradoxical, even irrational given the state of knowledge regarding the consequences of overgrazing. The phenomenon however appears inextricably linked with the objectives that farmers hold. In this research those objectives were elicited first and from their ranking two, 'asset value of cattle (representing cattle ownership and 'present value of economic returns', were chosen to develop an original bi-criteria Compromise Programming model to test various hypotheses postulated to explain the overgrazing behaviour. As part of the model a pasture productivity index is derived to estimate the pasture recovery cost. Different scenarios based on farmers' attitudes towards overgrazing, pasture costs and capital availability were analysed. The results of the model runs show that benefits from holding more cattle can outweigh the increased pasture recovery and maintenance costs. This result undermines the hypothesis that farmers practise overgrazing because they are unaware or uncaring caring about overgrazing costs. An appropriate approach to the problem of pasture degradation requires information on the economics,and its interplay with farmers' objectives, for a wide range of pasture recovery and maintenance methods. Seen within the context of farmers' objectives, some level of overgrazing appears rational. Advocacy of the simple 'no overgrazing' rule is an insufficient strategy to maintain the long-term sustainability of the beef production systems in Central Brazil. (C) 2004 Elsevier Ltd. All rights reserved.

Overgrazing in the Montado? The need for monitoring grazing pressure at paddock scale

Montados are presently facing the threat of either abandonment or intensification, and livestock overgrazing has been suspected of contributing to reduced natural regeneration and biodiversity. However, reliable data are to our knowledge, lacking. To avoid potential risks of overgrazing, an adaptive and efficient management is essential. In the present paper we review the main sources of complexity for grazing management linked with interactions among pasture, livestock and human decisions. We describe the overgrazing risk in montados and favour grazing pressure over stocking rate, as a key indicator for monitoring changes and support management decisions. We suggest the use of presently available imaging and communication technologies for assessing pasture dynamics and livestock spatial location. This simple and effective tools used for monitoring the grazing pressure, could provide an efficient day-to-day aid for farm managers’ operational use and also for rangeland research through data collection and analysis.

Potential soil carbon sequestration in overgrazed grassland ecosystems

Excessive grazing pressure is detrimental to plant productivity and may lead to declines in soil organic matter. Soil organic matter is an important source of plant nutrients and can enhance soil aggregation, limit soil erosion, and can also increase cation exchange and water holding capacities, and is, therefore, a key regulator of grassland ecosystem processes. Changes in grassland management which reverse the process of declining productivity can potentially lead to increased soil C. Thus, rehabilitation of areas degraded by overgrazing can potentially sequester atmospheric C. We compiled data from the literature to evaluate the influence of grazing intensity on soil C. Based on data contained within these studies, we ascertained a positive linear relationship between potential C sequestration and mean annual precipitation which we extrapolated to estimate global C sequestration potential with rehabilitation of overgrazed grassland. The GLASOD and IGBP DISCover data sets were integrated to generate a map of overgrazed grassland area for each of four severity classes on each continent. Our regression model predicted losses of soil C with decreased grazing intensity in drier areas (precipitation less than 333 mm yr(-1)), but substantial sequestration in wetter areas. Most (93%) C sequestration potential occurred in areas with MAP less than 1800 mm. Universal rehabilitation of overgrazed grasslands can sequester approximately 45 Tg C yr(-1), most of which can be achieved simply by cessation of overgrazing and implementation of moderate grazing intensity. Institutional level investments by governments may be required to sequester additional C.

Spatially-explicit modelling of grassland classes - an improved method of integrating a climate-based classification model with interpolated climate surfaces

Spatially-explicit modelling of grassland classes is important to site-specific planning for improving grassland and environmental management over large areas. In this study, a climate-based grassland classification model, the Comprehensive and Sequential Classification System (CSCS) was integrated with spatially interpolated climate data to classify grassland in Gansu province, China. The study area is characterized by complex topographic features imposed by plateaus, high mountains, basins and deserts. To improve the quality of the interpolated climate data and the quality of the spatial classification over this complex topography, three linear regression methods, namely an analytic method based on multiple regression and residues (AMMRR), a modification of the AMMRR method through adding the effect of slope and aspect to the interpolation analysis (M-AMMRR) and a method which replaces the IDW approach for residue interpolation in M-AMMRR with an ordinary kriging approach (I-AMMRR), for interpolating climate variables were evaluated. The interpolation outcomes from the best interpolation method were then used in the CSCS model to classify the grassland in the study area. Climate variables interpolated included the annual cumulative temperature and annual total precipitation. The results indicated that the AMMRR and M-AMMRR methods generated acceptable climate surfaces but the best model fit and cross validation result were achieved by the I-AMMRR method. Twenty-six grassland classes were classified for the study area. The four grassland vegetation classes that covered more than half of the total study area were "cool temperate-arid temperate zonal semi-desert", "cool temperate-humid forest steppe and deciduous broad-leaved forest", "temperate-extra-arid temperate zonal desert", and "frigid per-humid rain tundra and alpine meadow". The vegetation classification map generated in this study provides spatial information on the locations and extents of the different grassland classes. This information can be used to facilitate government agencies' decision-making in land-use planning and environmental management, and for vegetation and biodiversity conservation. The information can also be used to assist land managers in the estimation of safe carrying capacities which will help to prevent overgrazing and land degradation.

Defining and predicting the 'break of the season' for north-east Queensland grazing areas

For pasture growth in the semi-arid tropics of north-east Australia, where up to 80% of annual rainfall occurs between December and March, the timing and distribution of rainfall events is often more important than the total amount. In particular, the timing of the 'green break of the season' (GBOS) at the end of the dry season, when new pasture growth becomes available as forage and a live-weight gain is measured in cattle, affects several important management decisions that prevent overgrazing and pasture degradation. Currently, beef producers in the region use a GBOS rule based on rainfall (e. g. 40mm of rain over three days by 1 December) to define the event and make their management decisions. A survey of 16 beef producers in north-east Queensland shows three quarters of respondents use a rainfall amount that occurs in only half or less than half of all years at their location. In addition, only half the producers expect the GBOS to occur within two weeks of the median date calculated by the CSIRO plant growth days model GRIM. This result suggests that in the producer rules, either the rainfall quantity or the period of time over which the rain is expected, is unrealistic. Despite only 37% of beef producers indicating that they use a southern oscillation index (SOI) forecast in their decisions, cross validated LEPS (linear error in probability space) analyses showed both the average 3 month July-September SOI and the 2 month August-September SOI have significant forecast skill in predicting the probability of both the amount of wet season rainfall and the timing of the GBOS. The communication and implementation of a rigorous and realistic definition of the GBOS, and the likely impacts of anthropogenic climate change on the region are discussed in the context of the sustainable management of northern Australian rangelands.

A review of current knowledge of the weedy species Themeda quadrivalvis (grader grass)

This review of grader grass (Themeda quadrivalvis) attempts to collate current knowledge and identify knowledge gaps that may require further research. Grader grass is a tropical annual grass native to India that is now spread throughout many of the tropical regions of the world. In Australia, it has spread rapidly since its introduction in the 1930s and is now naturalised in the tropical areas of Queensland, the Northern Territory and Western Australia and extends south along the east coast to northern New South Wales. It is a vigorous grass with limited palatability, that is capable of invading native and improved pastures, cropping land and protected areas such as state and national parks. Grader grass can form dense monocultures that reduce biodiversity, decrease animal productivity and increase the fire hazard in the seasonally dry tropics. Control options are based on herbicides, grazing management and slashing, while overgrazing appears to favour grader grass. The effect of fire on grader grass is inconclusive and needs to be defined. Little is known about the biology and impacts of grader grass in agricultural and protected ecosystems in Australia. In particular, information is needed on soil seed bank longevity, seed production, germination and growth, which would allow the development of management strategies to control this weedy grass.

Demography of feral camels in central Australia and its relevance to population control

Since their release over 100 years ago, camels have spread across central Australia and increased in number. Increasingly, they are being seen as a pest, with observed impacts from overgrazing and damage to infrastructure such as fences. Irregular aerial surveys since 1983 and an interview-based survey in 1966 suggest that camels have been increasing at close to their maximum rate. A comparison of three models of population growth fitted to these, albeit limited, data suggests that the Northern Territory population has indeed been growing at an annual exponential rate of r = 0.074, or 8% per year, with little evidence of a density-dependent brake. A stage-structured model using life history data from a central Australian camel population suggests that this rate approximates the theoretical maximum. Elasticity analysis indicates that adult survival is by far the biggest influence on rate of increase and that a 9% reduction in survival from 96% is needed to stop the population growing. In contrast, at least 70% of mature females need to be sterilised to have a similar effect. In a benign environment, a population of large mammals such as camels is expected to grow exponentially until close to carrying capacity. This will frustrate control programs, because an ever-increasing number of animals will need to be removed for zero growth the longer that culling or harvesting effort is delayed. A population projection for 2008 suggests ~10 500 animals need to be harvested across the Northern Territory. Current harvests are well short of this. The ability of commercial harvesting to control camel populations in central Australia will depend on the value of animals, access to animals and the presence of alternative species to harvest when camels are at low density.

Wet season resting - economic insights from scenario modelling

Pasture degradation, particularly that attributable to overgrazing, is a significant problem across the northern Australian rangelands. Although grazing studies have identified the scope for wet season resting strategies to be used to rehabilitate degraded pastures, the economic outcome of these strategies has not been extensively demonstrated. An exploratory study of the prospective economic value of wet season resting is presented using an economic simulation model of a 28000 ha beef enterprise located in the Charters Towers region of north-eastern Australia to explore seven hypothetical scenarios centred on the projected performance of a wet season resting strategy. A series of 20-year simulations for a range of pasture recovery profiles, stocking capacity, animal productivity responses, beef prices and agistment options are compared with a baseline scenario of taking no action. Estimates of the net present value of the 20-year difference in total enterprise gross margins between the various resting options and the 'do nothing' option identify that wet season resting can offer a positive economic return for the range of scenarios examined, although this is contingent on the assumptions that are made concerning the trajectories of change in carrying capacity and animal productivity. Some implications for management and policy making to support the practical implementation of wet season resting strategies are discussed.

India's biodiversity hotspot under anthropogenic pressure: A case study of Nilgiri Biosphere Reserve

This paper presents data on the impact of biotic pressure in terms of grazing by livestock and wood cutting by humans on the plant community in the Nilgiri Biosphere Reserve of India. Grass, and herbaceous plant biomass, number of cattle dung piles, number of woody stems available and damaged by human activities and weed biomass were assessed at different proximity along transects radiating from village-forest boundary to forest interior to measure the ecological impact of livestock grazing and fire wood collection. The grass biomass was positively correlated to overgrazing indicating the adverse effect on natural vegetation by cattle. Woodcutting was intense along the forest boundary and significantly declined as distance increased. Similarly, weed biomass and number of thorny species declined positively with proximity from village-forest boundary and the weed biomass was significantly higher in the pastoral sites compared to residential sites. The results suggest that human impact adversely affects natural vegetation and promotes weed proliferation in forest areas adjoining human settlements in the ecologically important Nilgiri Biosphere Reserve. Continued anthropogenic pressure could cause reduction in fodder availability to large herbivores like elephants, which in turn leads to an increase in human-elephant conflict. (C) 2011 Elsevier GmbH. All rights reserved.

Brown trout habitat assessment on the River Bela catchment (as recommended by the strategic fisheries stock assessment task group 1995)

This is the Brown trout habitat assessment on the River Bela catchment produced by the Environment Agency North West in 1997. The Environment Agency (EA) and its predecessor the National Rivers Authority undertook strategic fish stock assessments in 1992 and 1995 on the River Bela catchment. These surveys found low numbers of brown trout {Salmo trutta) at some sites. Following this, habitat evaluation assessments were undertaken on the eleven poorest sites Factors probably responsible for declining trout populations on the three main tributaries of the Bela catchment include: Overgrazing by farm stock; Lack of suitable cover for parr; the absence of suitable spawning areas; existing potential of certain areas within the catchment not being utilised, due to poor dispersal. Habitat Improvement Schemes (H.I.S) are discussed and prioritised.

River Fowey SAP Final Plan

This is the River Fowey Salmon Action Plan Final document produced by the Environment Agency in 2003. This final Salmon Action Plan (SAP) for the River Fowey catchment has been produced after consideration of feedback from external consultation. It provides a list of the agreed issues and actions for the next five years to maintain and improve the River Fowey salmon stock. The actions presented within this final Salmon Action Plan clarify the important issues and factors currently limiting the salmon stock on the river. The resolution of these issues should ensure that a sustainable salmon population will be maintained for future generations. The main objective of the Fowey SAP therefore, is to maintain, improve and develop the Fowey salmon stocks to a sustainable level that, on the basis of historic catch records, the catchment can clearly support. Although the Fowey is passing its conservation limit, the consultees felt very strongly that there were two major factors limiting the salmon stock of the River Fowey- the overgrazing of Bodmin Moor and the use of the catchment for water supply by South West Water.

羊草对过度放牧和刈割的生理生态响应

放牧是草地最主要的利用方式，草地植物被家畜采食而部分或全部去叶是一个普遍存在的现象。内蒙古草原是我国北方地区最大的干旱半干旱草原，长期以来，过度放牧使草地的植被、土壤状况不断趋于恶化。由于过度放牧，草地植物正常的生理生态特性受到影响，光合作用能力、生长能力和繁殖更新能力等出现不同程度的降低。本文从动物－植物－土壤相互联系的角度出发，着重研究了过度放牧和刈割对内蒙古草原的一种典型植物—羊草（Leymus chinensis (Trin.) Tzevel.）形态、生长和生理的影响，以及羊草对放牧和刈割的生理生态响应，并得出以下主要结论： 1．过度放牧使土壤表层含水量、有机质含量和氮含量显著下降;羊草的叶量减少，比叶面积增大，节间缩短，分蘖减少;羊草的生物量根部分配比例增大，生殖器官则分配很少;羊草种群高度、盖度、密度和相对生物量均比对照显著降低。试验结果说明，过度放牧从短期可以影响到羊草种群和部分形态特征，长期则影响羊草的生物量分配模式，最终还使羊草的生境趋于恶化，不利于羊草的生长。同时，羊草对放牧也形成了一定的适应性。例如，比叶面积增大，增加了更多的光合叶面积;节间缩短可以躲避家畜啃食;生物量向根部集中，增大了对水分和养分的吸收面积等。 2．过度放牧使羊草的净光合速率显著降低;光合作用补偿点增大，光合作用饱和点却降低;蒸腾速率、气孔导度下降，暗呼吸速率增大;光系统Ⅱ的光化学效率、实际量子产量和光化学粹灭值均显著低于围封样地;瞬时和长期的水分利用效率也有不同程度的降低。试验结果表明，过度放牧强烈制约了羊草的光合作用能力和水分利用效率。而植物的光合作用是物质生产的基础，羊草光合能力的降低必然导致其生物产量的降低，从而也改变了羊草种群在整个生物群落中的作用和地位。 3．羊草在轻度（地上20％）和中度（地上40％）刈割条件下可以获得更大的地上累积生物量，表现为超补偿生长，并且地下生物量降低较少，相对生长速率较高，分蘖较多。而重度（地上80％）刈割可收获的地上累积生物量远少于对照，表现为欠补偿生长，且地下生物量大量减少，分蘖较少。在轻度或中度刈割条件下，施氮肥可以起到稳定维持植物生物产量的作用，但是重度刈割条件下，即使施加再多的氮肥也不能补偿植物生物量的损失。施磷肥对羊草的补偿性生长特性没有明显影响。而干旱加刈割处理的羊草不管是哪个刈割水平，均为欠补偿生长，地下生物量低，相对生长速率较低。 4．轻度刈割后羊草剩余叶片经过3天左右的生理恢复期后，表现出了明显的补偿性光合作用。中度和重度刈割羊草的生理恢复时间较长，没有表现出补偿性光合作用。刈割和施氮处理羊草剩余叶片的净光合速率变化和仅刈割处理（对照）基本上相同。刈割和干旱处理羊草剩余叶片的光合速率始终处于一个较低的水平，各刈割水平均没有表现出补偿性光合作用，主要是干旱导致气孔关闭，限制了叶片的气体交换。刈割后叶片气孔导度的增加可能是补偿性光合作用发生的重要原因。但叶片受到强烈伤害后，气孔导度虽然增加，其呼吸作用也增大，所以净光合速率还是较低。重度刈割叶片的叶绿素含量升高可以增加其光合作用潜力，为恢复正常生长作了生理上的准备，这可能是植物对刈割或放牧的一种生理适应性。 研究放牧条件下植物对动物采食的反应不仅具有重要的理论生态学意义，而且对提高植物的净生长量，维持草地持续的生产能力，实现草地的可持续利用具有重要的意义。研究草地主要植物对牲畜采食的补偿性生长效应及其条件，对合理利用草地可再生资源，确定合理的放牧强度有重要意义。应充分利用植物的超补偿效应，适时放牧，控制放牧强度，实现草地植物可食部分的超补偿生长，实现草地的最优化利用和生产力的最大化。

不同放牧强度下高山草甸生态系统碳氮分布格局和循环过程研究

本研究针对川西北高山草甸缺乏科学管理，过度放牧导致草场退化，并由此引发的一系列生态环境问题，选取红原县瓦切乡1996 年草地承包后形成的四个放牧强度草场，即不放牧、轻度（1.2 头牦牛hm-1）、中度（2.0 头牦牛hm-1）和重度放牧（2.9 头牦牛hm-1），作为研究对象，研究了不同放牧强度对草地植物-土壤系统中碳、氮这两个最基本物质的分布格局和循环过程的影响，并探讨了放牧干扰下高山草甸生态系统的管理。 1．放牧对草地植物群落物种组成，尤其是优势种，产生了明显的影响。不放牧、轻度、中度和重度放牧草地群落物种数分别为22，23，26，20 种，群落盖度分别是不放牧96.2%＞中度93.6%＞轻度89.7%＞重度73.6%。随放牧强度的增加， 原植物群落中的优势种垂穗鹅冠草（ Roegneria nutans ）、发草（Deschampsia caespitosa）和垂穗披碱草（Elymus nutans）等禾草逐渐被莎草科的川嵩草（Kobresia setchwanensis）和高山嵩草（Kobresia pygmaea）所取代成为优势种。同时，随放牧强度的增加，高原毛茛（Ranunculus brotherusii）、狼毒（Stellera chamaejasme）、鹅绒委陵菜（Potentilla anserina）和车前（Plantagodepressa）等杂类草的数量也随之增加。 2．生长季6～9 月份，草地植物地上和地下生物量（0～30cm）都是从6 月份开始增长，8 月份达到最高值，9 月份开始下降。每个月份，通常地上生物量以不放牧为最高，重度放牧总是显著小于不放牧；地下生物量随放牧强度的增加表现为增加的趋势，通常重度和中度放牧显著高于不放牧和轻度放牧草地。不放牧、轻度、中度和重度放牧草地6～9 月份4 个月的植物总生物量平均值分别是1543、1622、2295 和2449 g m-2，但随放牧强度的增加越来越来多的生物量被分配到了地下部分，地下生物量占总生物量比例的大小顺序分别是重度88%＞中度82%＞轻度76%＞不放牧69%。生物量这种变化主要是由于放牧使得群落优势种发生改变而引起的，其分配比例的变化体现了草地植物对放牧干扰的适应策略。 3．植物碳氮贮量的季节变化类似与生物量的变化。每个月份，不同放牧强度间植物地上碳氮的贮量有所不同，一般重度放牧会显著减少植物地上碳氮贮量。植物根系(0～30cm)碳氮贮量随放牧强度的增加表现为增加的趋势，通常重度和中度放牧显著高于不放牧和轻度放牧草地。不放牧、轻度、中度和重度放牧草地6～9 月份4 个月的植物总碳平均值分别是547、586、847 和909 g m-2，根系碳贮量占植物总碳的比例大小顺序分别是重度88%＞中度82%＞轻度76%＞不放牧69%；放牧、轻度、中度和重度放牧草地6～9 月份4 个月的植物总氮平均值分别是17、17、23 和26 g m-2，根系氮贮量占植物总氮的比例大小顺序分别是重度79%＞轻度71%＞中度70%＞不放牧65%。 4. 土壤有机碳贮量（0～30cm）的季节变化表现为7 月份略有下降，8 月开始增加，9 月份达到的最大值。土壤氮贮量的季节变化表现为随季节的推移逐渐增加的趋势。增加的放牧强度不同程度的增加土壤有机碳氮的贮量。不放牧、轻度、中度和重度放牧6～9 月份4 个月的土壤有机碳贮量的平均值分别是9.72、10.36、10.62 和11.74 kg m-2，土壤氮贮量分别为1.45、1.56、1.66 和1.83 kg m-2。土壤中有机碳（氮）的贮量都占到了植物-土壤系统有机碳（氮）的90%以上，但不同放牧强度之间的差异不明显。 5. 土壤氮的总硝化和反硝化，温室气体N2O 和CO2 的释放率的季节变化表现为从6 月份开始增加，7 月份达到最大值，8 月份开始下降，9 月份降为最小值。增加的放牧强度趋向于增加土壤氮的总硝化和反硝化作用，温室气体N2O和CO2 的释放率，通常情况下，中度放牧和重度放牧显著地加强了这些过程。 6．垂穗鹅冠草（Roegneria nutans）和川嵩草（Kobresia setchwanensis）凋落物在不同放牧强度下经过1 年的分解，两种凋落物的失重率及其碳氮的损失率3都随放牧增加表现为增加的趋势。在同一放牧强度下，川嵩草凋落物的失重率和碳氮的损失率都高于垂穗鹅冠草凋落物。 7. 尽管重度放牧显著增加了土壤碳氮的贮量，但同时也显著降低了植被群落盖度，降低了植物地上生物量，因此，久而久之会减少植物向土壤中的碳氮归还率；与不放牧和轻度放牧相比，重度放牧又显著增加了土壤CO2 和NO2 的排放量，这是草地生态系统碳氮损失的重要途径。由此可见，对于这些地处青藏高原的非常脆弱的高山草甸生态系统，长期重度放牧不仅导致植物生产力降低，而且将导致草地生态系统退化，甚至造成土壤中碳氮含量减少。 Long-term overgrazing has resulted in considerable deterioration in alpine meadowof the northwest Sichan Province. In order to explore management strategies for thesustainability of these alpine meadows, we selected four grasslands with differentgrazing intensity (no grazing-NG: 0, light grazing-LG: 1.2, moderate grazing-MG: 2.0,and heavy grazing-HG: 2.9 yaks ha-1) to evaluate carbon, nitrogen pools and cyclingprocesses within the plant-soil system in Waqie Village, Hongyuan County, Sichuan Province. 1. Grazing obviously changed the plant species composition, especially ondominant plant species. Total number of species is 22, 23, 26, and 20 for NG, LG, MGand HG, respectively. Vegetation coverage under different grazing intensity ranked inthe order of 96.2% for HG＞93.6% for MG＞89.7% for LG＞73.6% for NG. Thedominator of HG community shifted from grasses-Roegneria nutans andDeschampsia caespitosa dominated in the NG and LG sites into sedges-Kobresiapygmaea and K. setchwanensis. At the same time, with the increase of grazingintensity, the numbers of forbs, such as Ranunculus brotherusii, Stellera chamaejasme,Potentilla anserine and Plantago depressa, increased with grazing intensity. 2. Over the growing season, aboveground and belowground biomass showed a 5single peak pattern with the highest biomass in August. For each month, abovegroundbiomass usually was the highest in the NG site and lowest in the HG site.Belowground biomass showed a trend of increase as grazing intensity increased and itwas significantly higher in the HG and MG site than in the NG and LG sites. Totalplant biomass averaged over the growing season is 1543, 1622, 2295 and 2449 g m-2for NG, LG, MG and HG, respectively. The proportion of biomass to total plantbiomass for NG, LG, MG and HG is 88%, 82%, 76% and 69%, respectively. Higherallocation ratio for is an adaptive response of plant to grazing. 3. Carbon and nitrogen storage in plant components followed the similar seasonalpatterns as their biomass under different grazing intensities. Generally, heavy grazingsignificantly decreases aboveground biomass carbon and nitrogen compared to nograzing. Carbon and nitrogen storage in root tended to increase as grazing increasedand they are significantly higher in the HG and MG sites compared to the LG and NGsite. Total Carbon storage in plant system averaged over the growing season is 547,586, 847 and 909 g m-2 for NG, LG, MG and HG, respectively, while 17, 17, 23 and 26g m-2 for nitrogen. The proportion of carbon storage in root to total plant carbon forNG, LG, MG and HG is 88%, 82%, 76%, 69%, respectively, while 65%, 71%, 70%and 79% for nitrogen. 4. Carbon storage in soil (0-30cm) decreased slightly in July, then increased inAugust and peaked in September. Nitrogen storage in soil tended to increase withseason and grazing intensity. Total Carbon storage in soil averaged over the growingseason is 9.72, 10.36, 10.62 and11.74 kg m-2 for NG, LG, MG and HG, respectively,while 1.45, 1.56, 1.66 and 1.83 for nitrogen. The proportion of carbon (nitrogen)storage in soil to plant-soil system carbon (nitrogen) storage for NG, LG, MG and HGis more than 90%, which is not markedly different among different grazing intensities. 5. Gross nitrification, denitrification, CO2 and N2O flux rates in soil increasedfrom June to July and then declined until September, all of which tended to increasewith the increase of grazing intensity. Generally, heavy and moderate grazing intensitysignificantly enhanced these process compared to no and light grazing intensity. 6. After decomposing in situ for a year, relative weight, carbon and nitrogen loss in the litter of Roegneria nutans and Kobresia setchwanensis tended to increase asgrazing intensity increased. Under the same grazing intensity, relative weight, carbonand nitrogen loss in the litter of Kobresia setchwanensis were higher than these in thelitter of Roegneria nutans. 7. Although heavy grazing intensity resulted in higher levels of carbon andnitrogen in plant and soil, it decreased vegetation coverage and aboveground biomass,which are undesirable for livestock production and sustainable grassland development.What is more, heavy grazing could also introduce potential carbon and nitrogen lossvia increasing CO2 and N2O emission into the atmosphere. Grazing at moderateintensity resulted in a plant community dominated by forage grasses with highaboveground biomass productivity and N content. The alpine meadow ecosystems inTibetan Plateau are very fragile and evolve under increasing grazing intensity by largeherbivores; therefore, deterioration of the plant-soil system, and possible declines insoil C and N, are potential without proper management in the future.

A Global Crisis for Seagrass Ecosystems

Seagrasses, marine flowering plants, have a long evolutionary history but are now challenged with rapid environmental changes as a result of coastal human population pressures. Seagrasses provide key ecological services, including organic carbon production and export, nutrient cycling, sediment stabilization, enhanced biodiversity, and trophic transfers to adjacent habitats in tropical and temperate regions. They also serve as “coastal canaries,” global biological sentinels of increasing anthropogenic influences in coastal ecosystems, with large-scale losses reported worldwide. Multiple stressors, including sediment and nutrient runoff, physical disturbance, invasive species, disease, commercial fishing practices, aquaculture, overgrazing, algal blooms, and global warming, cause seagrass declines at scales of square meters to hundreds of square kilometers. Reported seagrass losses have led to increased awareness of the need for seagrass protection, monitoring, management, and restoration. However, seagrass science, which has rapidly grown, is disconnected from public awareness of seagrasses, which has lagged behind awareness of other coastal ecosystems. There is a critical need for a targeted global conservation effort that includes a reduction of watershed nutrient and sediment inputs to seagrass habitats and a targeted educational program informing regulators and the public of the value of seagrass meadows.