中国草畜平衡状态时空演变指示的草地生态保护格局

中国草原牧区作为重要生态安全屏障和草地畜牧业生产基地,其草畜平衡状态直接影响草地退化与恢复,进而影响草地生态系统服务能力的强弱。本文分析了2000—2015年主要草原牧区草地植被覆盖、牧草供给、草畜平衡状态的时空变化特征,深入探讨草地退化与恢复及载畜压力下草地生态系统保护与恢复空间格局。结果表明：过去16年主要草原牧区草地面积净减少约163万hm²,6.7%的草地出现植被覆盖退化,而5.4%的草地呈现植被覆盖明显恢复。天然草地牧草供给量以增加为主,年增率约0.3 kg/hm²,然而其载畜压力亦持续增加,不考虑补饲的载畜压力指数高达3.8,除内蒙古东北部、青藏高原中部仍有载畜潜力,其余多处于超载状态;考虑实际冷季补饲的载畜压力指数约3.1,内蒙古中东部有所缓解;假设冷季全额补饲则载畜压力指数减至1.9,内蒙古、青藏高原等区域明显缓解。叠加上述数据,本文针对自然保护地、牧区、半农半牧区和农区等不同区域的草地生态保护格局,提出了平衡草地生态保护与畜牧生产利用的不同发展策略。     

Driving Mechanism of Gross Primary Production Changes and Implications for Grassland Management on the Tibetan Plateau

The contribution of climatic change and anthropogenic activities to vegetation productivity are not fully understood. In this study, we determined potential climate-driven gross primary production (GPPp) using a process-based terrestrial ecosystem model, and actual gross primary production (GPPa) using MODIS Approach in alpine grasslands on the Tibetan Plateau from 2000 to 2015. The GPPa was influenced by both climatic change and anthropogenic activities. Gross primary production caused by anthropogenic activities (GPPh) was calculated as the difference between GPPp and GPPa. Approximately 75.63% and 24.37% of the area percentages of GPPa showed increasing and decreasing trends, respectively. Climatic change and anthropogenic activities were dominant factors responsible for approximately 42.90% and 32.72% of the increasing area percentage of GPPa, respectively. In contrast, climatic change and anthropogenic activities were responsible for approximately 16.88% and 7.49% of the decreasing area percentages of GPPa, respectively. The absolute values of the change trends of GPPp and GPPh of meadows were greater than those of steppes. The GPPp change values were greater than those of GPPh at all elevations, whereas both GPPp and GPPh showed decreasing trends when elevations were greater than or equal to 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. Climatic change had stronger effects on the GPPa changes when elevations were lower than 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. In contrast, anthropogenic activities had stronger effects on the GPPa changes when elevations were greater than or equal to 5000 m, 4600 m and 4800 m in meadows, steppes and all grasslands, respectively. Therefore, the causes of actual gross primary production changes varied with elevations, regions and grassland types, and grassland classification management should be considered on the Tibetan Plateau.     

北方农牧交错区草原利用与禁牧政策的关键问题研究

草原作为我国最大的陆地生态系统,对生态安全、生物多样性、畜牧业等具有重要的意义,但草原生态承载力有限,随着人口和社会经济压力的不断增加,对草原的过度利用导致草原生态破坏严重,草原生态系统面临巨大威胁。为了恢复和保护草原生态系统,2002年前后国家在草原破坏严重的地区实施禁牧政策。政策实施以来,草原得到很大程度的恢复,生态效果明显,但政策实施过程中也出现了一些新的问题。探索北方农牧交错区草原利用效率和存在的问题可为进一步制定相关政策提供依据,对北方农牧交错区的生态环境修复和可持续发展有重要的意义。本文通过对相关文献的综述和典型禁牧区的研究,从禁牧政策的效益、问题和农户支持度等方面,进行了研究和论述,主要结论包括：（1）北方农牧交错区草原生态承载力低,生态赤字严重。（2）禁牧政策虽对生态环境的改善起到很大作用,但在一些禁牧区,当地政府不能因地制宜实施禁牧政策,再加上配套实施和基础设施滞后,草场界限模糊以及政策宣传和监管力度不够等问题导致了新的草原退化,草原生态恢复大打折扣。（3）禁牧政策实施对农户的生产和生活造成一定的影响,部分农户无法顺利完成生计方式的转型,又因生态补偿标准低和补偿有失公平等问题无法弥补禁牧造成的经济损失,导致农户生活水平有所下降,加深了生态环境与农户生计之间的矛盾,部分农户对禁牧政策的支持度较低。     

青海湖流域草地产草量与MODIS植被指数的相关性分析

借鉴国内外基于遥感手段监测植被的方法,利用MODIS-NDVI遥感影像数据,探讨如何对草地变化进行监测。提取青海湖流域典型草原遥感影像植被指数,并与野外调查获得的79个样方生物量数据进行对比分析,建立了多个回归模型用于研究植被指数与草地产草量的相关关系。结果表明,植被指数与草地产草量之间存在较好的相关性,但是不同的回归模型与草地产草量相关性程度存在一定的差别,非线性回归模型优于一元线性回归模型,该方法的提出有助于监测青海湖流域草地变化情况。     

The conservation patterns of grassland ecosystem in response to the forage-livestock balance in North China

Being a key ecological security barrier and production base for grassland animal husbandry in China,the balance between grassland forage supply and livestock-carrying pressure in North China directly affects grassland degradation and restoration,thereby impacting grassland ecosystem services.This paper analyzes the spatiotemporal variation in grassland vegetation coverage,forage supply,and the balance between grassland forage supply and livestock-carrying pressure from 2000 to 2015 in North China.We then discuss the spatial pattern of grassland ecological conservation under the impacts of grassland degradation and restoration,and livestock-carrying pressure.Over the last 16 years,the total grassland area in North China decreased by about 16,000 km2,with vegetation coverage degraded by 6.7％ of the grasslands but significantly restored by another 5.4％ of grasslands.The provisioning of forage by natural grassland mainly increased over time,with an annual growth rate of approximately 0.3 kg/ha,but livestock-carrying pressure also increased continuously.The livestock-carrying pressure index without any supplementary feeding reached as high as 3.8.Apart from the potential livestock-carrying capacity in northeastern Inner Mongolia and the central Tibetan Plateau,most regions in North China are currently overloaded.Considering the actual supplementary feeding during the cold season,the livestock-carrying pressure index is about 3.1,with the livestock-carrying pressure mitigated in central and eastern Inner Mongolia.Assuming full supplementary feeding in the cold season,livestock-carrying pressure index will fall to 1.9,with the livestock-carrying pressure alleviated significantly in Inner Mongolia and on the Tibetan Plateau.Finally,we propose different conservation and development strategies to balance grassland ecological conservation and animal husbandry production in different regions of protected areas,pastoral areas,farming-pastoral ecotone,and farming areas,according to the grassland ecological protection patterns.     

Biophysical and Spectral Characteristics of Cool- and Warm-Season Grasslands under Three Land Management Practices in Eastern Kansas

Grasslands are the largest of the Earth's four major vegetation types and are among the most agriculturally productive lands. Grassland management practices alter biophysical factors, such as plant species composition, soil structure and chemistry, and primary productivity. Large-scale changes in land management practices can have significant impacts on available natural resources, therefore impacting a regional socioeconomics. For these reasons, an improved understanding of the geographic distribution of changing land management practices and how these changes affect grassland biophysical characteristics of an area is critical to improve land use planning and practices. This study investigated the spectral characteristics, as measured using satellite remotelysensed data, of three land management practices [grazing, haying, and management under Conservation Reserve Program (CRP)] on areas dominated by cool- and warm-season grasslands. The satellite imagery was acquired in May, July, and September in 1997 over Douglas County, Kansas. Biomass, vegetation cover, and species richness data were collected around the satellite overflight periods. Our results indicate that the biophysical characteristics and spectral reflectances are significantly different among the three management practices over cool- and warm-season grasslands. Interestingly, sites grazed by livestock had the highest species richness and the highest forb cover, although the total cover is almost the same as the other practices, and they have the highest near-infrared reflectance throughout the growing season.     

科尔沁沙地围封草地种子库特征

科尔沁沙地自由放牧草地围封7a后土壤种子库中植物种类有25种,其中一、二年生植物 19种。土壤种子库密度 3314粒·m^-2,其中,黄蒿(Artemisia scoparia)、狗尾草(Setaria viridis)、三芒草(Aristida adscensinis)等一年生植物种子占总数的95.3%,而多年生植物仅占4.7%。若以单子叶和双子叶植物统计,单子叶植物种子数占14%,双子叶植物的种子数占86%,其中豆科植物仅占2.4%。土壤种子库植物的种子数与其相应植物在植被中出现频率有明显的相关性。从种子库组成分析,围封7a的草地植被维持在黄蒿-杂类草混合植被阶段。围封草地对农牧生产方式转换频繁的科尔沁沙地草地植被恢复起着"种子岛"作用,它们的存在可以缩短周围被干扰草地恢复的时间,应该加强围封草地的管理利用研究。     

A Comparison of Public Lands and Farmlands for Grassland Bird Conservation

Midwestern states have invested extensively in grasslands for wildlife conservation, yet these public lands make up a minority of grassland habitat. How effective are public grasslands, relative to private lands, for conserving native songbird populations? I compare private and public lands in southern Minnesota using bird survey data from Conservation Reserve Program (CRP) fields and public lands and assessing fragmentation in a GIS. Bird abundance and diversity were greater on CRP lands. Vegetation composition, field isolation, and field size appear to explain differences in bird counts. Land cover data show that grassland habitat on public lands is scarce and widely scattered. The CRP provides more, and here better, habitat for grassland birds. Funding partly explains this disparity. Trends in farm set‐aside program rules and distribution, which can be vary greatly over time, will strongly influence the success or failure of biodiversity conservation in this region.     

Global and local policy forces for landscape perennialization in central North American agriculture

Farm production practices often focus on mitigating negative consequences of cropping – particularly annual crops like corn, cereals and oilseeds. Some of North America’s most-intensive farmlands are rapidly converting their remaining perennial cover to annual crops. While perennial cover like woodlands, grasslands and wetlands are valued for the many landscape services they provide, they are vulnerable to conversion to other cover types under drivers of landscape change. Conversions within farms constitute nuances rather than new land uses, yet landscape composition effects can be substantial when considering habitat, biodiversity, soil and water quality, carbon sequestration, and aesthetics. As the farm landscape becomes increasingly dominated by annual crop vegetation, the key drivers behind land cover types and management merit critical examination. This paper reviews recent studies on farmland composition and management in central Canada and the United States, identifying trajectories and magnitudes of landscape changes. To consider forces, both speculative examination of policies and information from farmer interviews help identify motivations for changes in perennial or annual proportions of farm landscapes. The paper concludes with forces that increase perennialization and existing or prospective pathways to improve the balance between annual and perennial vegetation.     

南澳岛退化草坡的植被恢复研究

在南澳岛建立次生草坡对照及草坡种植试验样地,观测群落植物多样性、土壤肥力及生物量变化,以探讨海岛退化草坡的植被恢复过程。结果显示,海岛迎风面上修建公路、风能发电场或开垦后的弃耕祼地在自然状况下很难恢复其植被,植物种类和数量甚至有所减少,植被覆盖度下降,需要进行人工植被恢复;在迎风面恶劣的环境下,次生草坡可能是一种偏途顶极,短时间内植物多样性变化不大。退化草坡的土壤肥力较低,开垦后若不及时恢复适当植被,情况会恶化。该岛草坡的生物量均较低,远低于该岛一般人工林或次生林的水平。海岛本身存在水分、土壤、生物条件等方面的脆弱性,在工程建设过程中应尽量避免对地形地貌和植被造成破坏,一旦破坏要尽快进行适生的人工植被恢复。     

Seasonal changes in the relationship between species richness and community biomass in grassland under grazing and exclosure, Horqin Sandy Land, northern China

How species diversity–productivity relationships respond to temporal dynamics and land use is still not clear in semi-arid grassland ecosystems. We analyzed seasonal changes of the relationships between vegetation cover, plant density, species richness, and aboveground biomass in grasslands under grazing and exclosure in the Horqin Sandy Land of northern China. Our results showed that in grazed and fenced grassland, vegetation cover, richness, and biomass were lower in April than in August, whereas plant density showed a reverse trend. Vegetation cover during the growing season and biomass in June and August were higher in fenced grassland than in grazed grassland, whereas plant density in April and June was lower in fenced grassland than in grazed grassland. A negative relationship between species richness and biomass was found in August in fenced grassland, and in grazed grassland the relationship between plant density and biomass changed from positive in April to negative in August. The relationship between the density of the dominant plant species and the total biomass also varied with seasonal changes and land use (grazing and exclosure). These results suggest that long-term grazing, seasonal changes, and their interaction significantly influence vegetation cover, plant density, and biomass in grasslands. Plant species competition in fenced grassland results in seasonal changes of the relationship between species richness and biomass. Long-term grazing also affects seasonal changes of the density and biomass of dominant plant species, which further affects the seasonal relationship between plant density and biomass in grasslands. Our study demonstrates the importance of temporal dynamics and land use in understanding the relationship between species richness and ecosystem function.     

Floristic uniformity across abrupt boundaries between Triodia hummock grassland and Acacia shrubland on an Australian desert sandplain

The tension between pyrophytic hummock grasslands and fire-sensitive mulga shrubland is a major ecological theme in central Australia. On a sandplain on the edge of the Tanami Desert, grassland and shrubland are juxtaposed with abrupt boundaries that cut across a subtle environmental gradient. We compare woody plant diversity among vegetation types and explore correlates of the distribution of woody plant species. Alpha diversity in grassland and shrubland was almost identical, but plot-level species richness was greater in grassland. Gamma (landscape) diversity was scarcely greater than alpha diversity. Few long-lived plants, and not even the dominant hummock grass and shrub, were exclusively associated with one vegetation type, but most common species were aligned with elements - soil texture, fire frequency and the extent of physical soil crusting - that characterise the environmental gradient between vegetation types. Most species were resprouters and there was no tendency for obligate seeders or facultative resprouters to be associated with the less fire-prone shrubland. Our data are consistent with the suggestion that hummock grasslands and mulga shrubland are alternative stable states maintained by fire-soil feedback loops and possibly also by competitive exclusion of pyrophytic species by Acacia aneura.     

The Gunnison's prairie dog structures a high desert grassland landscape as a keystone engineer

The influence of landscape spatial structure on ecological processes has recently received much attention. Comparisons are made here between the spatial structure of grasslands, and active and extirpated Gunnison's prairie dog (Cynomys gunnisoni Hollister) towns at the Petrified Forest National Park, Arizona, U.S.A. The spatial structure of bare ground was quatified using a box-counting technique to extract landscape fractal dimensions, D, and bare-ground patch size. These landscapes are fractal, and active prairie dog towns had higher fractal dimensions, i.e. a more homogeneous spatial structure as D approaches 2, than inactive towns, which had higher fractal dimensions than unmodified grasslands. Morisita's index suggested that shrubs were more randomly distributed on prairie dog towns and more aggregated on grassland habitats. The different spatial distributions of bare ground and shrubs have the potential to influence resource distributions between these habitats for both prairie dogs and other fauna. Consequently, the presence of prairie dogs in these grasslands increases grassland landscape heterogeneity at large spatial scales, potentially enhancing beta diversity.     

草原植被长势遥感监测研究进展

草原植被长势监测是草原监测的重要领域, 它能从宏观上揭示草原的生长状况及其动态变化, 从而为草原科学管理提供快速、准确的参考依据。目前长势监测主要利用遥感的方法, 即选择归一化植被指数NDVI作为反映植被生长状况的指标, 方法有同期对比法、植被生长过程曲线法、直接监测法。本文在总结草原长势监测进展与方法的同时, 指出了其中存在的问题--监测中过分依赖NDVI、不区分草原类型而使用同一种方法进行监测;对未来发展方向做了展望--监测中选用适宜植被指数、监测方法, 分区域、分类型的监测长势, 提高监测精度, 将长势监测与草原产草量、生产力结合, 为牧民生产提供指导。     

北方农牧交错带草原产草量遥感监测模型

及时准确地了解草原产草量的时空配置状况,对于科学合理地利用、管理草地,保证畜牧业生产持续稳定发展、改善生态环境等具有重要的意义。本文利用2005年的MODIS数据和同期野外实测的668个样方产草量数据,分析了5种植被指数和草地生物量之间的相关关系。研究表明:(1)分区模型优于不分区模型,在分区基础上建模更能反映产草量的实际情况;(2)通过线性、非线性模型和BP神经网络模型的对比,得出BP神经网络模型在拟合精度上优于线性和非线性模型,是最适宜监测北方农牧交错带草原产草量的模型;(3)5种植被指数中,NDVI和SAVI与草地生物量之间的拟合精度最高,是研究区最适宜使用的植被指数。     

Changes in intensity of wind erosion at different stages of degradation development in grasslands of Inner Mongolia, China

Overgrazing by increasing numbers of livestock in the Horqin Sandy Land of Inner Mongolia, China, has led to extensive degradation of the region's sandy steppes. Degraded grasslands are generally classified into four main types: fixed (least degradation), semi-fixed (light degradation), semi-shifting (moderate degradation) and shifting (severe degradation) sandy lands, representing four stages of degradation development. An experiment was conducted in the Horqin Sandy Land to investigate changes in intensity of wind erosion at different stages of degradation development in sandy grasslands and determine the extent to which surface wind erosion was affected by surface-related soil and vegetation factors through their effects on surface roughness length and wind regimes. Daily wind erosion rate was monitored at four sites of degraded grassland over an erosive period from 1 April to 10 June in 2001. Soil and vegetation properties for these sites were also measured twice: one in mid-April prior to the establishment of vegetation and again in mid-June after the establishment of vegetation. Relationships between surface roughness length and soil and vegetation variables were examined at each of the two stages of vegetation development. This study shows striking differences in the intensity of surface wind erosion among sites. The daily wind erosion rate in the fixed sandy land was, on average, only about 1/5 of the rate in the semi-fixed sandy land, 1/14 of the rate in the semi-shifting sandy land and 1/47 of the rate in the shifting sandy land suggesting a much higher resistance of the fixed sandy land to wind erosion compared to other sites. Differences in rate of wind erosion between sites were attributed to between-site differences in soil and vegetation properties that exerted significant effects on wind regimes by altering surface roughness length. At the pre-establishment stage of vegetation, surface roughness length was determined by a combination of litter amount on the ground, soil surface hardness and soil moisture content, with litter amount explaining the greatest proportion of the variation. At the post-establishment stage of vegetation, the development of the surface roughness effects was mainly governed by vegetation characteristics (vegetation cover in particular), while the effects of soil surface hardness and soil moisture on surface roughness length are likely to be masked by vegetation effects. The findings suggest that better management practices of restoring vegetation in degraded grasslands are required to reduce soil erosion losses and achieve a sustainable livestock production in the Horqin Sandy Land, an ecologically fragile sandy land ecosystem.     

基于卫星遥感数据改进区域尺度的显热通量模型

以西北半干旱地区的内蒙古农牧交错地带锡林郭勒盟为研究区,以不同退化程度的草地为研究对象,通过叶面积指数计算各像元的动力传输粗糙度长度,以改进显热通量算法;并结合植被／土壤组分温度分别计算基于亚像元的植被／土壤的显热通量。由敏感性分析和模型验证表明,改进的显热通量算法能够提高区域尺度的能量平衡计算精度。     

1982~2013年青藏高原高寒草地覆盖变化及与气候之间的关系

利用GIMMS NDVI数据和地面气象站台观测数据,对青藏高原1982~2013年高寒草地覆盖时空变化及其对气象因素的响应进行研究,结果表明：青藏高原高寒草地生长季NDVI表现为从东南到西北逐渐减少的趋势,近32 a来,整个高原草地生长季NDVI呈上升趋势,增加速率为0.000 3/a (p<0.05);高寒草地生长季NDVI年际变化具有空间异质性,整体为增加趋势,呈增加趋势的面积约占研究区域面积的75.3%,其中显著增加的占26.0% （p<0.05）,类型主要为分布在青藏高原东北部地区的高寒草甸;比例为4.7%,草地类型主要为高寒草原,主要分布在高原西部地区;基于生态地理分区的分析显示,青藏高原草地与降水、温度的相关关系具有明显的空间差异,高寒草地生长季NDVI均值与降水呈显著正相关,对降水的滞后效应显著;高原东北部温度较高,热量条件较好,降水为高寒草地生长季NDVI变化的主导因子;东中部地区降水充沛,温度则为高寒草地生长的制约因子;南部地区降水和温度都较适宜,均与高寒草地生长季NDVI相关性显著(p< 0.05),共同作用于草地的生长;中部和西部地区,气候因子与高寒草地生长季NDVI关系均不显著。     

天山北坡中东段天然草地光谱植被指数特征

据１９９２－１９９４年天山北坡中东段各种主要天然草地类型混合牧草群落光谱观测资料,牧草产量资料分析发现,天然草地牧草产量与光谱被指数都具有季节变化特征,呈现出低到高,再由高到低的变化规律;天然草地光谱植被指数可以较了地反映牧草产量的年际变化和不同类型天然草地的产量差异,由于降水等自然条件的影响,牧草产量的年份,光谱植被指数也高,牧草产量低的年份,光谱植被指数也低。     

干旱半干旱地区草原灌丛荒漠化及其 生物地球化学循环

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