中国草原产草量遥感监测

根据MODIS遥感数据和同期地面调查数据,对我国2005年草原产草量进行了系统估算。用MODIS数据计算全国草原的归一化植被指数NDVI,针对6个不同类型草原区建立了NDVI和地面样方的产草量之间的关系模型,用这些模型推算全国草原产草量分布。结论如下：（1）2005年我国草原有3个牧草高产中心,分别位于东北呼伦贝尔草原、锡林浩特草原和大兴安岭西麓;青海东部、四川西北部和甘肃中南部以及新疆西北部;（2）2005年全国草原干草总产量达到29421．39万t,平均单产达到829．67kg／hm^2干草;（3）2005年干草产量位列前7位的省区依次是内蒙古、青海、新疆、四川、西藏、黑龙江和甘肃;例如,内蒙古因草原面积大而成为我国第一大草原牧草生产省,2005年有6037．08万t干草;（4）总产草量位于前5位的草地类型依次为高寒草甸类、温性草原类、低地草甸类、温性草甸草原类与山地草甸类;（5）2005年8月份全国草原产草量与2004年同期相比总体持平;各草原大省的变化情况分别为：青海、甘肃2省区的草产量略有增加,青海增加了9．02％、甘肃增加了3．63％;内蒙古减少约3％;西藏、新疆和四川3省区基本与2004年同期持平。研究结果对我国草原监理、草原畜牧业发展和草地生态系统研究具有较大的参考价值。     

1982-2010年中国草地净初级生产力时空动态及其与气候因子的关系

植被净初级生产力（NPP）及其与气候变化的响应研究是全球变化的核心内容之一。论文基于长时间序列遥感数据和气象数据,通过光能利用率模型（Carnegie-Ames-Stanford approach, CASA模型）模拟了1982-2010 年中国草地NPP,进而分析其时空变化特征及其与气候水热因子的相关性。结果表明：（1）1982-2010年中国草地年平均NPP为282.0 gC m^-2a^-1,年总NPP的多年平均值为988.3 TgC;空间分布上呈现东南部高西北部低的特征。（2）近30年中国草地NPP增加速率为0.6 gC m^-2a^-1,呈增加趋势的面积占中国草地总面积的67.2%;总体上,中国草地NPP呈极显著和显著增加的比例（35.8%、8.0%）大于呈极显著和显著减少的比例（5.8%、4.8%）;NPP明显增加的区域主要包括青藏高原西部、阿拉善高原、新疆西部;明显降低的区域主要分布在内蒙古地区;不同年代际和不同草地类型的NPP变化趋势差异明显。（3）草地NPP与降水量的相关性高于与温度的相关性。不同草地类型NPP对气温、降水量的响应程度不同,其中温性荒漠草原 、温性草原、温性草甸草原的NPP与降水量均达到显著正相关（P<0.05）。     

中国西北部草地植被降水利用效率的时空格局

植被降水利用效率(PUE)是评价干旱、半干旱地区植被生产力对降水量时空动态响应特征的重要指标。利用光能利用率CASA(Carnegie-Ames-Stanford Approach)模型估算了2001—2010年中国西北七省草地植被净初级生产力(NPP),结合降水量的空间插值数据,分析了近十年草地植被PUE的空间分布、主要植被类型的PUE,及其时空格局的驱动因素。结果表明:(1)2001—2010年西北七省草地植被的平均PUE为0.68 g C m~(-2)mm~(-1)。在温带草地各类型中,PUE的大小顺序为草甸草原灌丛典型草原荒漠草原荒漠,各类型草地PUE之间差异显著;对于高寒草地而言,高寒草原的PUE显著高于高寒草甸;(2)温带草地PUE的空间分布与年降水量的关系呈抛物线形状(R~2=0.65,P0.001),PUE峰值出现在年降水量P=472.9 mm的地区;荒漠地区植被PUE的空间分布与年降水量的关系同样呈抛物线形状(R~2=0.63,P0.001),PUE峰值出现在年降水量P=263.2mm的地区;对于高寒草地而言,年降水量100 mm以下地区植被PUE变异较大,年降水量大于100 mm的地区植被PUE的空间分布随降水量的变化呈抛物线形状(R~2=0.47,P0.001),PUE峰值出现在P=559.2 mm的地区;(3)不同降水量区域,植被PUE的年际波动与气候因子的关系也有较大差别。在年降水量为200—1000 mm的地区,草地PUE的年际波动与年降水量的变化呈正相关;在年降水量高于1050 mm的地区,草地PUE的年际波动与年均温的相关性较强,相关系数最高可达到0.4。     

基于MODIS NPP数据的青海湖流域产草量与载畜量估算研究

快速评价区域草地生产力状况, 是制定牧区草畜平衡策略, 保障草地生态系统健康可持续发展的前提基础。基于MODIS NPP产品数据, 对青海湖流域草地生产力进行了估算和评价。结果表明: (1)牛羊可食性最高的高寒草甸、高寒草原和温性草原, 其单位面积产草量估算值的均方根误差RMSE为26.15 g·m-2, 表明该方法可以快速估算区域尺度的产草量。(2)全年干草产量为145.42万t, 其中能被牛羊直接采食利用的牧草共计59.18万t, 理论载畜量为81.07万羊单位; (3)影响单位面积干草产量的主要气候因子, 海拔3500 m以下地区, 是活动积温且与单位面积干草产量呈负相关关系; 3500 m以上地区, 是温度且与单位面积产草量呈正相关关系。研究结果可为高寒地区合理规划牧业生产活动、生态补偿等提供科学依据和决策支持, 也可为全国其他牧区的草原产草量的估算提供参考。     

2000—2015年青藏高原草地归一化植被指数对降水变化的响应

降水变化是造成青藏高原草地植被生长年际变异的重要因素,降水量、分配方式及发生时间是降水变化的重要特征.利用2000—2015年青藏高原及附近区域145个气象站点的降水资料,以年降水量表征降水整体状况,以改进的降水集度(PCI)表征年内降水的分配状况,以定义的降水重心(PC)表征降水的集中时期,分析青藏高原降水变化的时空特征;并进一步以归一化植被指数最大值(NDVI_max)表征植被生长状况,探讨了青藏高原草地对降水年际变化的响应.结果表明: 青藏高原年降水量和PCI存在明显的梯度特征,PC在西藏南部形成中心.青藏高原灌丛草地NDVI_max年际变化对PCI变化响应敏感,降水越均匀越有利于NDVI_max的增加,但受到降水量的限制;高寒草甸对降水特征没有表现出显著的相关关系;草原植被NDVI_max的年际变化同时受PCI和PC的控制;高寒荒漠植被NDVI_max的年际变化主要受降水量的控制.在研究降水变化对青藏高原不同类型植被的影响时,除降水量之外,还需进一步考虑降水的分配格局等特征.     

不同利用状况下草原遥感估产模型

在内蒙古自治区的温性草甸草原、温性草原、温性荒漠草原、温性草原化荒漠和温性荒漠5种具有代表性的草地类型区地面观测数据的基础上,考虑草地的利用状况信息,分类建立了产草量与4种植被指数(由MODIS数据计算得到)的回归估产模型,将利用状况这一定性变量作为虚拟变量与遥感估算模型相结合,找出了3种利用状况下的鲜草产量最优混合估算模型和估算指数。结果表明:(1)EVI是反映产草量变化的最好指标,分类构建的模型平均测产精度达到了80%;(2)将利用状况作为虚拟变量考虑之后建立的混合测算模型精度达到了79%,明显高于利用状况未知时构建的混合模型的精度,比分类建模应用更简洁方便。     

2001—2010年黄河流域生态系统植被净第一性生产力变化及气候因素驱动分析

基于MODIS-NDVI遥感数据,利用CASA模型分析黄河流域2001—2010年植被净第一性生产力（NPP）的空间分布格局,并结合同期气温和降水量数据,分别从不同空间和时间尺度上分析了黄河流域6种生态系统类型区域植被NPP的变化趋势,并对其与气候因素的相关关系进行分析.结果表明： 植被NPP空间分布呈西北低、东南高的分布特征,平均NPP年总量为108.53 Tg C,植被NPP的分布与生态系统类型呈现较高的相关性;2001—2010年,植被NPP总体呈上升趋势但波动较大,55.4%的面积呈现增加趋势,不同生态系统类型区域呈现不同的变化趋势;在年际水平上,黄河流域植被NPP变化与气候因素没有显著相关性,但在月际水平上呈现了较高的相关性,降水量和气温对植被NPP变化的影响作用相当;不同生态系统类型对气候因素呈现不同的相关性质以及时滞效应,草地对降水量的响应存在一定程度的时滞效应,荒漠对气温存在时滞效应.     

锡林郭勒盟草地生态系统服务功能价值动态估算

定量评价草地生态系统服务功能价值及其动态变化,对草地资源保护具有重要意义。以锡林郭勒盟为研究区域,选用2000—2015年MODIS数据和年值降水量数据,构建了定量的生态服务价值估算体系,对草地生态系统提供产品、营养物质循环、维持碳氧平衡、涵养水源、保持土壤及文化娱乐六种服务功能进行了动态估算和对比分析,并探讨了研究区域内各旗、市、县草地生态服务价值的动态变化情况。研究结果表明:2000—2015年锡林郭勒盟草地生态系统提供的总服务价值年际增长率为2.52%,年均增值33.71亿元,呈波动上升的趋势。但各旗、市、县之间草地资源发展不平衡(年际增长率范围-0.46%—1.71%),尤其在正镶白旗(年际增长率-0.30%)和太仆寺旗(年际增长率-0.46%)两地服务价值负增长;不同草地生态系统服务功能提供的服务价值相差悬殊,维持碳氧平衡功能约占比当年总价值35%,而提供产品功能仅占比约5%,对草地生态系统保护起着至关重要作用的涵养水源功能也仅占比约1.5%。为动态估算内蒙古自治区,乃至京津冀地区的草地生态系统服务功能价值提供借鉴。     

蒙古高原草原火行为的时空格局与影响因子

采用GIS空间分析方法和L3JRC遥感卫星数据,研究了2000-2007年间蒙古高原草原火行为的时空分布规律,比较了中国内蒙古自治区和蒙古人民共和国草原火行为的差异,分析了植被、气候与人文因素等对草原火行为的影响.结果表明：不同植被类型间的过火率存在极显著差异（P<0.001）,为草甸草原>典型草原>荒漠草原,蒙古人民共和国草原过火率显著高于中国内蒙古自治区(P<0.001),过火频次的分布格局与过火迹地相一致.草原火行为存在明显的年际变化特征,草甸草原(r²=-0.54,P<0.05)和典型草原（r²=-0.61,P<0.05）的年过火率与年降雨量呈负相关关系;草原火集中在降水较少、风速较大的春、秋两季.中国内蒙古自治区的人口密度和载畜密度远高于蒙古人民共和国,而过火率则相反,表明人文因素,尤其是过度放牧是导致中国内蒙古自治区和蒙古人民共和国火行为差异的主要原因.     

科尔沁草甸草地归一化植被指数与气象因子的关系

利用内蒙古科左后旗草甸草地2000—2006年MODIS的8 d合成归一化植被指数(NDVI)资料和逐日气象资料,分析了研究区NDVI的季节变化和年际变化特点以及NDVI与气象因子的关系.结果表明：季节变化过程中,研究区水汽压与NDVI的相关程度明显大于降水量;积温和累积降水量共同控制着各年草地的返青速度,草地增长期（6、7月）的降水量对NDVI年最大值的影响比年总降水量更显著;时滞分析表明,水汽压对之后约12 d的NDVI有持续的显著影响,平均气温的时滞为11～15 d,降水量对NDVI影响的累积时滞双重效应可达36～52 d.     

Remote sensing monitoring upon the grass production in China

Using MODIS remote sensing data and ground truth data, a thorough investigation was conducted to monitor the productivity of grasslands in China for the year 2005. The Normalized Difference Vegetation Index (NDVI) was first computed from the MODIS data. Then the data from the NDVI images were used to correlate with the grass yield data from the ground sampling campaigns. Six regional models were accordingly established from the correlation for estimation of grass production in the six main types of steppe in China. The main results from the estimation could be summarized as follows: (1) High grass productivity in 2005 was obtained in the following 3 regions: the grassland covering Hulunbuir, Xilinhaote, and the western Daxing'anling, the region including the eastern Qinghai, the northwestern Sichuan and the mid-southern Gansu, and the northwestern Xinjiang region. (2) Total hay output from the grasslands in China amounted to 294213.86 thousand tons in 2005 with an average yield of 829.67 kg/hm2. (3) The following 7 provinces were the largest grass producers in China: Inner Mongolia, Qinghai, Xinjiang, Sichuan, Tibet, Heilongjiang and Gansu. For example, Inner Mongolia produced 60370.82 thousand tons of hay in 2005, and hence became the No. 1 grass producer of China. (4) Among the steppe types, the following 5 had the largest grass production: Alpine meadow, Temperate steppe, Low-land meadow, Temperate meadow steppe and Montane meadow with total production accounting for 62.2% in China. (5) Grass production of the entire China in August 2005 remained at the same level as that in August 2004. However, the situations of major grassland provinces were different: grass production in both Qinghai and Gansu in 2005 increased to 9.02% and 3.63%, respectively, when compared with that in 2004. The grass production in Inner Mongolia decreased by 3%, while the production in Tibet, Xinjiang and Sichuan remains unchanged when compared with that in 2004. These results were very important for grassland administration, pasture grazing and grassland ecosystem studies in China.     

Remote sensing monitoring upon the grass production in China

Using MODIS remote sensing data and ground truth data, a thorough investigation was conducted to monitor the productivity of grasslands in China for the year 2005. The Normalized Difference Vegetation Index (NDVI) was first computed from the MODIS data. Then the data from the NDVI images were used to correlate with the grass yield data from the ground sampling campaigns. Six regional models were accordingly established from the correlation for estimation of grass production in the six main types of steppe in China. The main results from the estimation could be summarized as follows: (1) High grass productivity in 2005 was obtained in the following 3 regions: the grassland covering Hulunbuir, Xilinhaote, and the western Daxing'anling, the region including the eastern Qinghai, the northwestern Sichuan and the mid-southern Gansu, and the northwestern Xinjiang region. (2) Total hay output from the grasslands in China amounted to 294213.86 thousand tons in 2005 with an average yield of 829.67 kg/hm2. (3) The following 7 provinces were the largest grass producers in China: Inner Mongolia, Qinghai, Xinjiang, Sichuan, Tibet, Heilongjiang and Gansu. For example, Inner Mongolia produced 60370.82 thousand tons of hay in 2005, and hence became the No. 1 grass producer of China. (4) Among the steppe types, the following 5 had the largest grass production: Alpine meadow, Temperate steppe, Low-land meadow, Temperate meadow steppe and Montane meadow with total production accounting for 62.2% in China. (5) Grass production of the entire China in August 2005 remained at the same level as that in August 2004. However, the situations of major grassland provinces were different: grass production in both Qinghai and Gansu in 2005 increased to 9.02% and 3.63%, respectively, when compared with that in 2004. The grass production in Inner Mongolia decreased by 3%, while the production in Tibet, Xinjiang and Sichuan remains unchanged when compared with that in 2004. These results were very important for grassland administration, pasture grazing and grassland ecosystem studies in China.     

Plant responsiveness to variation in precipitation and nitrogen is consistent across the compositional diversity of a California annual grassland

Question: How does responsiveness to water and Nitrogen (N) availability vary across the compositional and functional diversity that exists in a mesic California annual grassland plant community? Location: Northern California annual grassland. Methods: A mesocosm system was used to simulate average annual precipitation totals and dry and wet year extremes observed in northern California mesic grasslands. The effects of precipitation and N availability on biomass and fecundity were measured on three different vegetation types, a mixed grass forb community, and a forb and a grass monoculture. The treatment effects on plant community composition were examined in the mixed species community. Results: While growth and seed production of the three vegetation types was inherently different, their responses to variation in precipitation and N were statistically similar. Plant density, shoot biomass, and seed production tended to increase with greater water availability in all vegetation types, with the exception of a consistent growth reduction in high precipitation (1245 mm) plots in the first year of the study. Shoot biomass responded positively to N addition, an effect that increased with greater water availability. Nitrogen addition had little effect on plant density or seed production. In the mixed grass‐forb community, biomass responsiveness to water and N treatments were consistently driven by the shoot growth of Avena barbata, the dominant grass species. Conclusions: Vegetation responses to changes in precipitation and N availability were consistent across a range of composition and structural diversity in this study. Plant growth and seed production were sensitive to both increased and decreased precipitation totals, and the magnitude of these responses to N availability varied depending on soil moisture conditions. Our results suggest the impacts of changing precipitation regimes and N deposition on annual productivity of California grasslands may be predictable under different climate scenarios across a range of plant communities.     

2000-2015年宁夏草地净初级生产力时空特征及其气候响应

草地是宁夏陆地生态系统的重要组成部分,估算其净初级生产力（NPP）对宁夏草地可持续利用与管理至关重要。采用MODIS数据和CASA模型对2000-2015年间宁夏草地生态系统NPP进行了估算,通过一元线性回归趋势分析、Hurst指数等方法研究草地NPP的时空变化规律及未来演变趋势,并分析草地NPP与气象因子的相关性。结果表明：（1）基于CASA模型的宁夏草地NPP模拟精度高,其估算值与实测多年草地NPP均值具有良好的线性关系（R=0.93,P < 0.01）,与MOD17产品的草地NPP空间分布基本一致。（2）近16 a宁夏草地年均NPP为148.28 g C m^-2 a^-1,且存在波动上升的趋势,其线性增长率为3.84 g C m^-2 a^-1（P < 0.01）。（3）宁夏草地NPP整体处于上升趋势,草地NPP增长的草地面积达98%,且其增率自南向北递减;宁夏草地NPP的Hurst指数在0.27-0.81之间,均值为0.53,大部分草地的NPP变化趋势具有较强同向持续性。（4）在年时间尺度上,宁夏草地NPP主要受降水量的影响,与气温的相关性较弱;在月时间尺度上,生长季草地NPP与月总降水量的相关性高,且不存在时间滞后响应现象,而与月均温的响应则存在1个月的时间滞后性,宁夏大面积分布的干草原与荒漠草原NPP对气温响应滞后是导致这一现象发生的主要原因。     

Interannual variability of NDVI and its relationship to climate for North American shrublands and grasslands

Abstract. Our objective was to analyse the interannual variability of different characteristics of the seasonal dynamics of NDVI and their relationships with climatic variables for grassland and shrubland sites of North America. We selected twenty-five sites located in relatively undisturbed areas. We analysed the variability of seven traits derived from the annual dynamics of the NDVI at each site: the annual integral, the difference between maximum and minimum NDVI, the dates of the inflection points of a double logistic model fitted to the NDVI curve, the difference between these dates, the date of maximum NDVI, and the coefficient of determination of the double logistic model. The temporal variability of traits that integrated aspects of primary productivity over the year was lower than those related to seasonality. This suggests that from year to year, grassland and shrubland ecosystems would differ more in the timing of production and senescence than in the total amount of carbon fixed. The integral of NDVI showed less temporal variability than annual precipitation. The coefficient of variation of both precipitation and the NDVI integral were positively related. The slope of the relationship was significantly lower than 1, indicating that the variability of ecosystem function is a lower proportion of the variability of annual precipitation in areas with a high relative variability of this climatic variable than in areas of low variability. The variability of most of the NDVI traits analysed showed a negative and, in general, non-linear relationship with annual precipitation. The same kind of relationship has been reported elsewhere for annual precipitation and its coefficient of variation. Mean annual precipitation has been reported as the main control of above-ground net primary production in grassland and shrubland ecosystems. Our results suggest that this climatic variable is also associated with the interannual variability of carbon gains, such as the primary production and its seasonality.     

Ecological dynamic model of grassland and its practical verification

Based on the physico-biophysical considerations, mathematical analysis and some approximate formulations generally adopted in meteorology and ecology, an ecological dynamic model of grassland is developed. The model consists of three interactive variables, I.e. The biomass of living grass, the biomass of wilted grass, and the soil wetness. The major biophysical processes are represented in parameterization formulas, and the model parameters can be determined inversely by using the observational climatological and ecological data. Some major parameters are adjusted by this method to fit the data (although incomplete) in the Inner Mongolia grassland, and other secondary parameters are estimated through sensitivity studies. The model results are well agreed with reality, e.g., (I) the maintenance of grassland requires a minimum amount of annual precipitation (approximately 300 mm); (ii) there is a significant relationship between the annual precipitation and the biomass of living grass; and (iii) the overgrazing will eventually result in desertification. A specific emphasis is put on the shading effect of the wilted grass accumulated on the soil surface. It effectively reduces the soil surface temperature and the evaporation, hence benefits the maintenance of grassland and the reduction of water loss in the soil.     

Ecological dynamic model of grassland and its practical verification

Based on the physico-biophysical considerations, mathematical analysis and some approximate formulations generally adopted in meteorology and ecology, an ecological dynamic model of grassland is developed. The model consists of three interactive variables, i.e. the bio-mass of living grass, the biomass of wilted grass, and the soil wetness. The major biophysical processes are represented in parameterization formulas, and the model parameters can be determined inversely by using the observational climatological and ecological data. Some major parameters are adjusted by this method to fit the data (although incomplete) in the Inner Mongolia grassland, and other secondary parameters are estimated through sensitivity studies. The model results are well agreed with reality, e.g., (i) the maintenance of grassland requires a minimum amount of annual precipitation (approximately 300 mm); (ii) there is a significant relationship between the annual precipitation and the biomass of living grass; and (iii) the overgrazing will eventually result in desertification. A specific emphasis is put on the shading effect of the wilted grass accumulated on the soil surface. It effectively reduces the soil surface temperature and the evaporation, hence benefits the maintenance of grassland and the reduction of water loss in the soil.     

黄土高原近10年植被覆盖的动态变化及驱动力

基于Timesat的非对称高斯函数(AG)拟合法重建MODIS-NDVI数据,利用像元二分模型估算了黄土高原近10年的植被覆盖度(VC),并分析了年植被覆盖度的变化趋势和其与降水温度的相关性。研究结果表明:黄土高原植被覆盖度总体上呈现东南高西北低、由东南向西北递减的特征。其中森林生态系统平均覆盖度最高,灌木、草地生态系统次之,荒漠生态系统最低,空间差异明显。2010年森林生态系统植被覆盖度达到81.6%,主要包括太行山、吕梁山和秦岭地区。暖温带森林区植被组成以落叶阔叶林为主,覆盖度常年较高,为80%以上。西北部温带草原区,植被覆盖度达到38.8%。温带草地主要依水分梯度,由东南到西北分布有以旱生性多年生草本植物为主的典型草原,植被覆盖度呈现相应的递减趋势。黄土高原总面积78.6%的地区年植被覆盖度呈增加趋势;而占总面积19.4%的地区年植被覆盖度呈下降趋势。在空间分布上,植被覆盖度显著增加的区域主要分布在榆林至延安周边地区和秦岭一带;植被覆盖度显著减少区域沿兰州至银川呈条带状分布。