伊犁地区土地覆被变化及其对植被碳储量的影响

以伊犁地区为研究对象,以2005、2010年和2015年的土地覆被类型数据和植被功能型分类方案为依据,并利用植被固碳模型,分析了近10 a伊犁地区土地覆被变化特征及其对植被碳储量的影响。结果表明:1）伊犁地区土地覆被变化主要表现为农业用地、林地和建筑用地呈增加趋势,年变化率分别为0.007%、0.031%和0.001%,草地和灌木呈减少趋势,年变化率分别为0.003%和0.1%。2）10 a增加农业用地的面积为923.9 km²,主要的转化来源为草地,占转化总量的83.9%,同时也有78.8%的农业用地转化为草地。3）由于土地覆被的变化、植被净初级生产力以及不同土地覆被类型之间碳转化系数的影响,导致植被的碳储量总体上减少了2.48×10⁵ t。从整体上来看,伊犁地区的农业用地和草地的变化最为显著,土地覆被的变化导致的植被碳储量整体呈减少的趋势。由此可以得出,近10 a伊犁地区草地和农业用地的变化是影响植被碳储量的重要因素。     

Estimating regional forest productivity and water yield using an ecosystem model linked to a GIS

We used the PnET-II model of forest carbon and water balances to estimate regional forest productivity and runoff for the northeastern United States. The model was run at 30 arc sec resolution (approximately 1 km) in conjunction with a Geographic Information System that contained monthly climate data and a satellite-derived land cover map. Predicted net primary production (NPP) ranged from 700 to 1450 g m² yr¹ with a regional mean of 1084 g m² yr¹. Validation at a number of locations within the region showed close agreement between predicted and observed values. Disagreement at two sites was proportional to differences between measured foliar N concentrations and values used in the model. Predicted runoff ranged from 24 to 150 cm yr¹with a regional mean of 63 cm yr¹. Predictions agreed well with observed values from U.S. Geologic Survey watersheds across the region although there was a slight bias towards overprediction at high elevations and underprediction at lower elevations.Spatial patterns in NPP followed patterns of precipitation and growing degree days, depending on the degree of predicted water versus energy limitation within each forest type. Randomized sensitivity analyses indicated that NPP within hardwood and pine forests was limited by variables controlling water availability (precipitation and soil water holding capacity) to a greater extent than foliar nitrogen, suggesting greater limitations by water than nitrogen for these forest types. In contrast, spruce-fir NPP was not sensitive to water availability and was highly sensitivity to foliar N, indicating greater limitation by available nitrogen. Although more work is needed to fully understand the relative importance of water versus nitrogen limitation in northeastern forests, these results suggests that spatial patterns of NPP for hardwoods and pines can be largely captured using currently available data sets, while substantial uncertainties exist for spruce-fir.     

基于LPJ模型的中亚地区植被净初级生产力与蒸散模拟

中亚干旱区是对全球气候变化最敏感的区域之一,以草地和耕地为主的植被类型极易受到水资源短缺和人为等因素影响,导致生态环境极易恶化,故分析其植被净初级生产力(NPP)和蒸散(ET)变化特征及对气候的响应具有重要意义。本研究利用LPJ模型模拟中亚地区1982-2012年NPP和ET,并分析其在中亚潜在植被类型中的空间分布和变化特征。结果表明,1)NPP和ET的高低值空间分布基本一致,高值区主要分布在林地、草林地混合区以及耕地区,低值区主要分布在植被稀少的荒漠周边区域和哈萨克中部草地区;2)NPP总量和ET总量均呈波动上升趋势,其中NPP年度变化范围在469.59~1 130.26 Tg C·a-1,年均值为737.24 Tg C·a-1(185.57 g C·m-2·a-1),ET范围在695.53~1 047.69 km3·a-1,年均值为850.46 km3·a-1(214.07 mm·a-1);3)影响中亚地区植被NPP和ET变化的气候因子主要为降水,温度影响相对较弱;4)吉尔吉斯斯坦和塔吉克斯坦植被生产力增长较快,哈萨克斯坦、乌兹别克斯坦和新疆较为稳定,土库曼斯坦植被生产力出现下降现象。     

毛乌素沙地南缘禾草杂类草草地地上部生物量动态及光能转化率研究

对分布于毛乌素沙地南缘的禾草杂类草草地地上部生物量动态,净第一生产力和光能转化率进行了研究,由于过度利用,该草地群落出现退化,一、二年生植物及对家畜有害植物的盖度占草地群落总盖度的５０－６０％。４－１１月期间,其地上部生物量（ＤＭ）的变化呈单峰曲线,最大值出现在９月１３日,为９４．００ｇ／ｍ＾２,草地群落地上部净第一性生产力（ＤＭ）为８４．９４ｇ／（ｍ＾２·年）,以能量计算,则为１２２５．６３ｋＪ     

基于CASA模型的甘肃省草地净初级生产力研究

利用基于遥感数据的光能利用模型-CASA模型估算了2005年甘肃草地生态系统NPP,分析了其空间格局,以及地形因素对草地NPP的影响。(1)实测数据与模拟结果对比表明,修正后的CA-SA模型的可操作性强,仅利用地面气象数据和遥感数据就可以对草地生产力进行模拟,模拟效果较好。(2)2005年甘肃省草地NPP总量为3.76×1013g/(m2.a),最高值达790.56g/(m2.a),年均值为139.15g/(m2.a),由西南向东北逐渐减少。(3)草地NPP季节变化非常明显,夏季NPP达到最大值;冬季植被基本停止生长,草地NPP值最低。4)在海拔3 000～3 500m区域、25°～30°坡度以及东坡草地NPP均达到较高水平。     

陆地生态系统净初级生产力的时空动态模拟研究进展

陆地生态系统净初级生产力(Net Primary Productivity,NPP)研究是全球变化的核心内容之一,反映了植被每年通过光合作用所固定的碳总量。近年来将遥感数据引入到NPP的模型设计和估算中已成为了一种新的发展方向,它利用遥感获得的全覆盖数据,使区域及全球尺度的NPP估算成为可能。回顾了NPP研究历史,综合分析了气候相关统计模型、生态系统过程模型和光能利用率模型的优缺点;以CASA、C-FIX和BIOME-BGC这3种遥感参数模型为例,阐述和分析了该类模型的特点以及国内外的研究进展,提出了NPP模型存在的问题和未来的发展方向。     

青海高原草地净初级生产力和降水利用效率时空特征

为了探究青海高原草地净初级生产力（Net primary productivity,NPP）和降水利用效率（Precipitation use efficiency,PUE）的时空特征,基于遥感估算的NPP数据和降水空间插值数据,采用地理空间统计法分析了2001—2017年青海高原草地NPP和PUE的时空特征。结果表明：2001—2017年青海高原草地NPP均值为42.81 gC·m^-2,其中高值区域主要分布在青海高原的东部和南部,低值区域主要分布在青海高原的西北部。2001—2017年青海高原草地NPP年际变化总体较为平稳,以年均速率0.09 gC·m^-2呈微弱的波动上升。2001—2017年青海高原草地PUE均值为0.089 gC·m^-2·mm^-1,其中高值区域主要分布在青海高原的东部和南部,低值区域主要分布在青海高原的西部和西北部。2001—2017年青海高原草地PUE年际变化呈微弱的波动下降趋势,下降速率为年均0.0023 gC·m^-2·mm^-1。2001—2017年青海高原草地PUE年际变化整体上与降水年际变化为负相关。本研究为青海高原草地可持续利用提供了重要理论参考和数据支撑。     

西南地区植被NPP对多尺度气象干旱的响应

[目的] 为研究植被对不同时间尺度干旱的响应机理,明确西南地区极端干旱事件频发对植被生长产生严重的负面影响。[方法] 基于西南地区2001—2019年的NPP数据和1~24个月连续尺度的SPEI数据,采用相关分析法、最大值合成法及显著性检验等方法探究西南地区不同地貌类型植被NPP对多尺度SPEI的响应特征,并分析不同植被类型NPP对多尺度SPEI响应的差异性。[结果] (1)在年际、季节及生长季尺度,植被NPP与1~24个月尺度SPEI的响应均以1－3月尺度占主导,表明植被NPP对短期干旱变化具有较好的响应,不同地貌分区响应时间表现出差异性。(2)空间上,植被NPP与1~24个月尺度SPEI的最大相关系数呈明显的异质性和季节性差异。年际相关性表现出从东南—西北呈显著正相关—显著负相关的变化趋势,季节相关性表现为夏季均以显著负相关占主导,春季、秋季和冬季均以显著正相关占主导,表明西南地区的夏季温度高且湿润,使植被生长受限,生长季正、负相关关系的区域面积比例相差不大,且呈显著正相关面积最大的地区为广西丘陵,呈显著负相关面积最大的地区为若尔盖高原。(3)不同植被类型NPP对1~24个月尺度SPEI的响应具有一定差异,尽管草地、灌丛、林地对SPEI的响应特征基本相似,但所有植被类型NPP在夏季随SPEI尺度的缩短呈负相关趋势越强烈。表明在夏季高温干旱条件下,各种植被类型都更易受到干旱的影响。[结论] 研究结果为西南地区生态系统的保护和修复提供有效的科学支撑,同时,为防灾减灾及应对气候变化提供重要的理论依据,有助于制定更具针对性的政策和措施,推动西南地区的可持续发展。     

Estimation of biomass,net primary production and net ecosystem production of China's forests based on the 1999–2003 National Forest Inventory

Abstract

The National Forest Inventory (NFI) is an important resource for estimating the national carbon (C) balance. Based on the volume, biomass, annual biomass increment and litterfall of different forest types and the 6th NFI in China, the hyperbolic relationships between them were established and net primary production (NPP) and net ecosystem production (NEP) were estimated accordingly. The results showed that the total biomass, NPP and NEP of China's forests were 5.06 Pg C, 0.68 Pg C year^?1 and 0.21 Pg C year^?1, respectively. The area-weighted mean biomass, NPP and NEP were 35.43 Mg C ha^?1, 4.76 Mg C ha^?1 year^?1 and 1.47 Mg C ha^?1 year^?1 and varied from 13.36 to 79.89 Mg C ha^?1, from 2.13 to 9.15 Mg C ha^?1 year^?1 and from ?0.16 to 5.80 Mg C ha^?1 year^?1, respectively. The carbon sequestration was composed mainly of Betula and Populus forest, subtropical evergreen broadleaved forest and subtropical mixed evergreen–deciduous broadleaved forest, whereas Pinus massoniana forest and P. tabulaeformis forest were carbon sources. This study provides a method to calculate the biomass, NPP and NEP of forest ecosystems using the NFI, and may be useful for evaluating terrestrial carbon balance at regional and global levels.     

Estimation of spatial and temporal changes in net primary production based on Carnegie Ames Stanford Approach (CASA) model in semi-arid rangelands of SemiromCounty,Iran

Net primary production (NPP) is an indicator of rangeland ecosystem function. This research assessed the potential of the Carnegie Ames Stanford Approach (CASA) model for estimating NPP and its spatial and temporal changes in semi-arid rangelands of Semirom County, Iran. Using CASA model, we estimated the NPP values based on monthly climate data and the normalized difference vegetation index (NDVI) obtained from the MODIS sensor. Regression analysis was then applied to compare the estimated production data with observed production data. The spatial and temporal changes in NPP and light utilization efficiency (LUE) were investigated in different rangeland vegetation types. The standardized precipitation index (SPI) was also calculated at different time scales and the correlation of SPI with NPP changes was determined. The results indicated that the estimated NPP values varied from 0.00 to 74.48 g C/(m²?a). The observed and estimated NPP values had different correlations, depending on rangeland conditions and vegetation types. The highest and lowest correlations were respectively observed in Astragalus spp.-Agropyronspp. rangeland (R²=0.75) with good condition and Gundeliaspp.-Cousiniaspp. rangeland (R²=0.36) with poor and very poor conditions. The maximum and minimum LUE values were found in Astragalus spp.-Agropyronspp. rangeland (0.117 g C/MJ) with good condition and annual grasses-annual forbs rangeland (0.010 g C/MJ), respectively. According to the correlations between SPI and NPP changes, the effects of drought periods on NPP depended on vegetation types and rangeland conditions. Annual plants had the highest drought sensitivity while shrubs exhibited the lowest drought sensitivity. The positive effects of wet periods on NPP were less evident in degraded areas where the destructive effects of drought were more prominent. Therefore, determining vegetation types and rangeland conditions is essential in NPP estimation. The findings of this study confirmed the potential of the CASA for estimating rangeland production. Therefore, the model output maps can be used to evaluate, monitor and optimize rangeland management in semi-arid rangelands of Iran where MODIS NPP products are not available.