吉林省西部草地NPP时空特征与影响因素

利用2000--2006年MOD17A3数据集的年均NPP数据,通过GIS技术定量分析了吉林省西部草地NPP的时空变化特征及其自然和人文影响因素.结果表明:过去7年吉林省西部草地NPP平均值为232.14 g C·m~(-2)·a~(-1),NPP在200～300 g C·m~(-2)·a~(-1)的草地面积占草地总面积的59.47%;77.60%的草地NPP呈增加趋势,NPP增加极显著的草地面积占草地总面积的15.00%;水分条件是吉林省西部草地生长的主要控制因素;居民地对吉林省西部草地NPP的影响远大于道路,尤其在2 km以内.

Abstract：

By using the annual net primary productivity (NPP) data from 2000-2006 MOD17A3 dataset and the GIS technique, the spatiotemporal characteristics of grassland NPP in western Ji-lin Province were studied, with the related affecting factors analyzed. During the past seven years, the mean grassland NPP in this province was 232. 14 g C·m~(-2)·a~(-1), and the grassland area with a NPP of 200-300 g C·m~(-2)·a~(-1) accounted for 59. 47% of the total. 77.60% of the grassland had an increasing NPP, and the grassland area with a remarkable increase of NPP accounted for 15.00% of the total. Water condition was the main controlling factor for grass growth, and residential points had far more effects than roads, especially within 2 km from grass-land, on the NPP.     

Carbon balance along the Northeast China Transect (NECT-IGBP)

The Northeast China Transect (NECT) along a precipitation gradient was used to cal-culate the carbon balance of different vegetation types, land-use practices and temporal scales. NECT consists of mixed coniferous-broadleaved forest ecosystems, meadow steppe ecosystemsand typical steppe ecosystems. Analyses of the C budget were carried out with field measurement based on dark enclosed chamber techniques and alkali absorption methods, and the application of the CENTURY model. Results indicated that: (1) soil CO_2 flux had a strong diurnal and seasonal variation influenced by grassland type and land-use practices. However, the seasonal variation on soil CO_2 fluxes did not show obvious changes between non-grazing and grazing Leymus chinensis dominated grasslands. (2) Hourly soil CO_2 fluxes mainly depended on temperature, while dailyCO_2 fluxes were affected both by temperature and moisture. (3) NPP of the three typical ecosys-tems showed linear relationships with inter-annual precipitation, but total soil carbon of those eco-systems did not. NPP and total soil carbon values decreased westward with decreasing precipita-tion. (4) Model simulation of NPP and total soil carbon showed that mean annual precipitation was the major limiting factor for ecosystem productivity along NECT. (5) Mean annual carbon budget is the largest for the mixed coniferous- broadleaved forest ecosystem (503.2 gC m~(-2)a~(-1)), followed bythe meadow steppe ecosystem (227.1 gC m~(-2)a~(-1)), and the lowest being the typical steppe eco-system (175.8 gC m~(-2)a~(-1)). This study shows that concurrent field measurements of terrestrial ecosystems including the soil and plant systems with surface layer measurements along the wa-ter-driven IGBP-NECT are valuable in understanding the mechanisms driving the carbon cycle in different vegetation types under different land-use practices. Future transect research should be emphasized.     

广西西江流域植被净初级生产力时空分布特征及其影响因素

植被净初级生产力(net primary productivity,NPP)是流域生态系统功能的关键因子之一。本研究基于Carnegie-Ames-Stanford approach(CASA)模型,综合利用2003—2012年MODIS序列遥感数据、植被数据和气象数据,对广西西江流域植被NPP进行估算,并分析其时空格局及其影响因素。结果表明:2003—2012年广西西江流域的NPP年均值为524.67 g C·m~(-2)·a~(-1);NPP高值主要集中在研究区南部和东部地区,而中部地区NPP值相对较低;从地形上看,河谷平原植被NPP值较低,丘陵山地植被NPP值较高;不同类型植被对应的NPP值差异较大;常绿阔叶林NPP值最高,为788 g C·m~(-2)·a~(-1);栽培作物NPP值最低,为386 g C·m~(-2)·a~(-1)。2003—2012年研究区植被NPP平均值位于430.05~602.48g C·m~(-2)·a~(-1),总体呈现波动下降趋势。NPP呈现减少趋势的区域占研究区总面积的88.89%;7—10月NPP值较高,1—3月NPP值较低。NPP与年均降水量总体呈负相关关系,与年均温呈正相关关系;NPP受气候因子(降水量、气温)的综合影响,且植被NPP与气候因子(降水量、气温)相关性较密切,复相关系数为0.67。     

封育对科尔沁沙地小叶锦鸡儿群落植被特征及空间异质性的影响

以科尔沁沙地小叶锦鸡儿群落为对象,分析了放牧和不同封育年限下小叶锦鸡儿群落的植被特征及植被分布的小尺度空间异质性.结果表明:放牧和封育样地内植被均以1年生草本植物为主,物种数没有明显差异;封育6年、封育12年样地的植株密度分别为(124.46±5.22)株·m~(-2)和(203.05±10.38)株·m~2,显著高于放牧样地(P<0.05);封育样地的Shannon-Wiener多样性指数、Simpson多样性指数、Pielou均匀度指数均低于放牧样地,并随着封育年限的增加而减小;封育样地植被分布的小尺度空间异质性小于放牧样地,并且封育年限越长,空间异质性越小.

Abstract：

This paper studied the vegetation characteristics and small-scale spatial heterogeneity of Caragana mirophylla community in Horqin Sandy Land in northeast Inner Mongolia of China under grazing and under 6-and 12 years enclosure, aimed to assess the effects of grazing and enclosure on vegetation restoration. In the sampling plots of grazing and different years enclosure, the species composition of C. mirophylla community all dominated by annual herbaceous plants. The species richness in grazed plot and in the plots enclosed for 6 and 12 years was 22, 19, and 20, respectively, with no significant difference. In the plots enclosed for 6 and 12 years, the plant density was (124.46±5.22) plants·m~(-2) and (203. 05±10. 38) plants·m~(-2), respec- tively, being significantly higher than that in grazed plot, which suggested that enclosure was an effective method to accelerate the vegetation restoration in Sandy Land. The Shannon-Wiener index, Simpson species diversity, and Pielou evenness in enclosed plots were lower than those in grazed plot, and decreased with increasing enclosure duration. The small-scale spatial heteroge-neity of vegetation in enclosed plots was smaller than that in grazed plot. The longer the enclosure duration, the smaller the spatial heterogeneity was.     

Response of vegetation and soil carbon accumulation rate for China's mature forest on climate change北大核心CSCD

Aims This study aims to evaluate the impacts of future climate change on vegetation and soil carbon accumulation rate in China's forests. Methods The vegetation and soil carbon storage were predicted by the atmosphere-vegetation interaction model (AVIM2) based on B2 climate change scenario during the period of 1981 2040. This study focused on mature forests in China and the forested area maintained constant over the study period. The carbon accumulation rate in year t is defined as the carbon storage of year t minus that of year t 1. Important findings Under B2 climate change scenario, mean air temperature in China's forested area was projected to rise from 7.8 °C in 1981 to 9.0 °C in 2040. The total vegetation carbon storage was then estimated to increase from 8.56 Pg C in 1981 to 9.79 Pg C in 2040, meanwhile total vegetation carbon accumulation rate was estimated to fluctuate between 0.054 0.076 Pg C•a1, with the average of 0.022 Pg C•a1. The total soil carbon storage was estimated to increase from 30.2 Pg C in 1981 to 30.72 Pg C in 2040, and total soil carbon accumulation rate was estimated to vary in the range of 0.035 0.072 Pg C•a1, with the mean of 0.010 Pg C•a1. The response of vegetation and soil carbon accumulation rate to climate change had significant spatial difference in China although the two time series did not show significant trend over the study period. Our results also showed warming was not in favor of forest carbon accumulation, so in the northeastern and southeastern forested area, especially in the Changbai Mountain, with highest temperature increase in the future, the vegetation and soil carbon accumulation rate were estimated to decrease greatly. However, in the southern of southwestern forested area and other forested area, with relatively less temperature increase, the vegetation and soil carbon accumulation rate was estimated to increase in the future.     

Modeling the interannual variation and response to climate change scenarios in gross and net primary productivity of Pinus elliottii forest in subtropical China

In this study, the BIOME-BGC model, a biogeochemical model, was used and validated to estimate GPP (Gross Primary Productivity) and NPP (Net Primary Productivity) of Pinus elliottii forest in red soil hilly region and their responses to inter-annual climate variability during the period of 1993–2004 and climate change scenarios in the future. Results showed that the average total GPP and NPP were 1941 g C m^?2a^?1 and 695 g C m^?2a^?1, and GPP and NPP showed an increasing trend during the study period. The precipitation was the key factor controlling the GPP and NPP variation. Scenario analysis showed that doubled CO₂ concentration would not benefit for GPP and NPP with less than 1.5% decrease. When CO₂ concentration fixed, GPP responded positively to precipitation change only, and temperature increase by 1.5°C with precipitation increase, while NPP responded positively to precipitation change only. When CO₂ concentration was doubled and climate was changed, GPP and NPP responded positively to precipitation change, and GPP also responded positively to temperature increase by 1.5°C with precipitation change.     

CO2 flux dynamics and its limiting factors in the alpine shrub-meadow and steppe-meadow on the Qinghai-Xizang Plateau北大核心CSCD

Aims Alpine shrub-meadows and steppe-meadows are the two dominant vegetation types on the Qinghai-Xizang Plateau, and plays an important role in regional carbon cycling. However, little is known about the temporal- spatial patterns and drivers of CO2 fluxes in these two ecosystem types. Methods Based on five years of consecutive eddy covariance measurements (2004-2008) in an eastern alpine shrub-meadow at Haibei and a hinterland alpine steppe-meadow at Damxung, we investigated the seasonal and annual variation of net ecosystem productivity (NEP) and its components, i.e. gross primary productivity (GPP) and ecosystem respiration (Re). Important findings The CO2 fluxes (NEP, GPP and Re) were larger in the shrub-meadow than in the steppe-meadow during the study period. The shrub-meadow functioned as a carbon sink through the five years, with the mean annual NEP of 70 g C·m-2·a-1. However, the steppe-meadow acted as a carbon neutral, with mean annual NEP of -5 g C·m-2·a-1. The CO2 fluxes of steppe-meadow exhibited large variability due to the inter-Annual and seasonal variations in precipitation, ranging from a carbon sink (54 g C·m-2·a-1) in 2008 to a carbon source (-88 g C·m-2·a-1) in 2006. The differences in carbon budget between the two alpine ecosystems were firstly attributed to the discrepancy of normalized difference vegetation index (NDVI) because NDVI was the direct factor regulating the seasonal and inter-Annual NEP. Secondly, the shrub-meadow had higher carbon use efficiency (CUE), which was substantially determined by annual precipitation (PPT) and NDVI. Our results also indicated that the environmental drivers of CO2 fluxes were also different between these two alpine ecosystems. The structure equation model analyses showed that air temperature (Ta) determined the seasonal variations of CO2 fluxes in the shrub-meadow, with NEP and GPP being positively correlated with Ta. By contrast, the seasonal CO22 fluxes in the steppe-meadow were primarily co-regulated by soil water content (SWC) and Ta, and increased with the increase of SWC and Ta. In addition, the changes of Re during the growing season in two ecosystems were directly affected by GPP and soil temperature at 5 cm depth (Ts), while Re during non-growing season were determined by Ts. These results demonstrate that the synergy of soil water and temperature played crucial roles in determining NEP and GPP of the two alpine meadows on the Qinghai-Xizang Plateau. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

西北干旱区植被净初级生产力的遥感估算及时空差异原因

植被净初级生产力(NPP)是评价陆地生态系统的重要参数。本文基于2000—2014年的MODIS NDVI数据,结合西北干旱区的自然环境特点,从土地覆盖类型、分类的精度、辐射数据的选取、计算公式的选择等方面对CASA模型进行改进和率定,进一步估算了西北干旱区的NPP,并分析了NPP的时空变化特征。结果表明:经验证改进的CASA模型对于干旱半干旱区植被NPP的模拟效果较好,可以反映研究区的植被生长及分布状况,西北干旱区多年平均植被NPP为191.63 g C·m~(-2)·a~(-1);西北干旱区植被NPP分布具有明显的区域差异性,总体上呈现出西北、东南高,中间低的特征;在年际变化上,NPP总体上呈增加趋势,线性增长率为2.98 g C·m~(-2)·a~(-1),且不同植被类型的NPP增长率不同,耕地增长最快,其次是灌丛,最低的是林地;对西北干旱区不同植被类型的NPP与气候因子(气温、降水)的相关性分析表明,总体上植被生物量与降水的相关系数为0.538(P0.05),与气温的相关系数为0.394,说明研究区植被NPP与降水的相关性高于气温;且不同植被类型与气候因子的相关性具有差异性。     

Carbon stock assessment for a forest-to-coffee conversion landscape in Sumber-Jaya (Lampung, Indonesia): from allometric equations to land use change analysis

The change in stored carbon (C) stocks was assessed for a 700 km~2 area where forestcover decreased from 60% to 10% in the last 30 years. At the same time, the area under coffee increased from 7% to 70% with a gradual evolution from open "sun coffee" systems to multi-strata "shade coffee" systems that provide a partial compensation for C loss. The use of a generic tropi-cal forest rather than tree-specific allometric equation can lead to substantial (up to 100%) overes-timates of aboveground biomass depending on wood density and tree shape. The shoot: root ratio (biomass) of coffee shifted with age, from the 4∶1 value often assumed for tropical trees to 2∶1.Annual aboveground C stock accumulation rates during the establishment stage after slash-and-burn land clearing were 1, close to 2 or 3.5 Mg C ha~(-1)a~(-1) for sun coffee, shade coffee and fallowregrowth, respectively. Forest remnants, shade coffee and sun coffee had soil C stocks in the up-per 30 cm of the soil that were 79%, 60% or 45%, respectively, of the values expected for primary forest in Sumatra. Total C stock (time averaged, above-0.3 m in the soil) for forest, shade and sun coffee was 262, 82 and 52 Mg C ha~(-1), respectively. In the 1970-1984 period, while forest cover was reduced from 59.5% to 19.7%, the landscape lost on average 6.8 Mg C ha~(-1) a~(-1). In the1984-2000 period forest cover was further reduced to 12.6%, but the landscape lost only 0.39 MgC ha~(-1) a~(-1), as forest loss was partially compensated by an increase in shade coffee systems. Conversion of all current sun coffee to shade coffee systems while protecting the remaining forest,could increase average landscape level C stocks by 10 Mg ha~(-1) over a time frame of say 20 years,or 0.5 Mg C ha~(-1) a~(-1).     

辽东栎林净初级生产力对气候变化情景响应的模拟与分析

An ecosystem process model, BIOME-BGC, was used to explore the sensitivity of net primary productivity (NPP) of an oak (Quercus liaotungensis Koidz) forest ecosystem in Beijing area to global climate changes caused by increasing atmospheric CO₂ concentrations. Firstly we tested the model, and validated the modeled outputs using observational data; the outputs of BIOME-BGC model were consistent with observed soil water content and annual NPP. Secondly the potential impacts of climate change on the oak forest ecosystem were predicted with BIOME-BGC model. We found that the simulated NPP was much more sensitive to a 20% precipitation increase or a doubling of atmospheric CO₂ from 355 to 710 祄ol/mol than to a 2 ℃ temperature increase. Our results also indicated that the effects of elevated CO₂ and climate change on the response of NPP were not interactive.     

黄土高原草地净初级生产力时空动态及其影响因素

利用光能利用效率模型(Carnegie-Ames-Stanford approach,CASA)模拟2000-2015年黄土高原草地净初级生产力(NPP),分析黄土高原草地NPP的时空动态、NPP变化稳定性和持续性特征,从植被类型、地形因素、气候变化和人类活动4个方面探讨黄土高原草地NPP的影响因素.结果表明:黄土高原草地NPP的平均值为202.93 g C·m^-2·a^-1,其年际变化特征呈现显著增加的趋势,平均年增加速率为2.43 g C·m^-2·a^-1;分布具有明显的空间异质性,大体呈南高北低的状态.黄土高原草地NPP呈增加趋势的区域占总草地面积的91.2%,主要分布在陕西省的大部分地区、甘肃陇东及陇中地区和青海等地.草地NPP变化较为稳定的区域主要集中在鄂尔多斯的南部地区、陕北地区和甘肃等地.大部分地区草地NPP未来的变化趋势与过去一致,且陕西省的大部分地区以及甘肃省的陇中及陇东地区的草地NPP将呈现持续显著增加的趋势.坡面草地的平均NPP值最高,为703.37 g C·m^-2·a^-1;而高山亚高山草地NPP平均值最低,为57.28 g C·m^-2·a^-1.高海拔地区的草地NPP较高,而平原及丘陵地带草地NPP相对较低.研究期间黄土高原降水量的增加对草地NPP的增加具有明显的促进作用;人类活动诸如过度放牧状况的改善以及退耕还草等政策的实施对黄土高原草地NPP的增加也具有重要作用.     

长白山高山苔原季节性雪斑土壤呼吸对温度响应的模拟研究

利用LI-8100土壤呼吸测定系统, 在室内控制温度条件下测定了长白山高山苔原季节性雪斑大白花地榆(Sanguisorba sitchensis (=S. stipulata))群落土壤呼吸对温度的响应过程, 并根据野外连续测定的全年温度, 估算了雪斑群落土壤呼吸的季节变化, 同时模拟气温升高对土壤呼吸的影响。雪斑土壤温度全年大部分时间维持在0 ℃以上, 极端温度变动幅度不超过20 ℃。模拟计算了10 cm深土壤的呼吸强度, 海拔2 036 m处为307.1 g C·m^-2·a^-1, 海拔2 260 m处的呼吸量为270.9 g C·m^-2·a^-1。由于积雪时间长, 冬季呼吸占很大比例, 而且随着海拔的升高比例加大。从海拔2 036 m到2 260 m, 积雪期土壤呼吸分别占全年的42.5% (125.4 g C·m^-2·a^-1)和49.7% (128.7 g C·m^-2·a^-1)。模拟气温升高1 ℃并假设积雪时间减少20天, 冬天的呼吸量减少8%左右, 但全年总呼吸量增加8%左右。升温后, 平均增加的呼吸量为0.25 g C·kg^-1·a^-1 (或22.65 g C·m^-2·a^-1), 冬季呼吸量减少0.118 g C·kg^-1·season^-1 (或10.81 g C·m^-2·season^-1)。     

1999—2015年若尔盖草原湿地净初级生产力时空变化

植被净初级生产力(NPP)是草原湿地生态系统碳收支平衡和气候变化的核心内容之一。本研究基于植被指数、气象数据(降水和气温)、植被类型数据,利用CASA模型对若尔盖草原湿地1999—2015年NPP进行估算,分析了若尔盖草原湿地NPP时空格局特征及其与气候因子的关系。结果表明: NPP实测值与模拟值之间显著相关,R²为0.78,均方根误差为120.3 g C·m^-2·a^-1;研究区年均和生长季(4—9月)NPP分别为329.0、229.4 g C·m^-2·a^-1,年际间波动明显,以2.3、1.6 g C·m^-2·a^-1的微弱趋势下降,不同植被类型的年均及生长季NPP的年际波动与整个研究区的波动趋势基本一致;年均和生长季NPP的变化斜率分别为-21.3～18.7、-31.5～23.1 g C·m^-2·a^-1,显著增加的面积分别占研究区总面积的0.3%和0.7%,主要分布于森林覆盖区和湿地生态补偿区;显著下降的面积分别占研究区总面积的1.4%和6.4%,主要分布于人类活动集中的地区;研究区不同植被的固碳能力存在差异,其中,森林最强,草地次之,湿地最弱;降水是影响草原湿地植被NPP的主导气候因子。     

中国陆地植被净初级生产力遥感估算

该文在综合分析已有光能利用率模型的基础上,构建了一个净初级生产力(NPP)遥感估算模型,该模型体现了3方面的特色:1)将植被覆盖分类引入模型,并考虑植被覆盖分类精度对NPP估算的影响,由它们共同决定不同植被覆盖类型的归一化植被指数(NDVI)最大值;2)根据误差最小的原则,利用中国的NPP实测数据,模拟出各植被类型的最大光能利用率,使之更符合中国的实际情况;3)根据区域蒸散模型来模拟水分胁迫因子,与土壤水分子模型相比,这在一定程度上对有关参数实行了简化,使其实际的可操作性得到加强。模拟结果表明,1989~1993年中国陆地植被NPP平均值为3.12 Pg C (1 Pg=10¹⁵ g),NPP模拟值与观测值比较接近,690个实测点的平均相对误差为4.5%;进一步与其它模型模拟结果以及前人研究结果的比较表明,该文所构建的NPP遥感估算模型具有一定的可靠性,说明在区域及全球尺度上,利用地理信息系统技术将遥感数据和各种观测数据集成在一起,并对NPP模型进行参数校正,基本上可以实现全球范围不同生态系统NPP的动态监测。     

青海省植被光能利用率模拟研究

借鉴了MODIS-PSN、CASA、GLO-PEM、VPM等光能利用率NPP模型的优点,同时充分考虑了研究区域其植被光能利用率和环境因素的典型特点。根据研究区域相关文献资料和NPP实测数据,模拟出主要植被类型的最大光能利用率。同时,特别细化了草地和灌丛最大光能利用率的估算步骤。采用蒸散比算法和陆地生态模型(TEM),根据Liebig定律,计算了对最大光能利用率产生影响的环境综合胁迫因子。估算了青海省主要植被类型的光能利用率,并详细分析了其空间分布和季相变化特征。结果表明:2006年青海省植被平均光能利用率介于0.026-0.403gC/MJ之间,平均值为0.096gC/MJ。青海省植被光能利用率的分布具有明显的地带性,呈由西北向东南逐渐递增的趋势。其随季节的推移变化比较明显,2006年植被月平均光能利用率在0.057-0.157gC/MJ之间,峰值出现在7月份,主要的光能利用率累积发生在5-9月份。     

利用CASA模型估算我国植被净第一性生产力

基于地理信息系统和卫星遥感应用技术,利用CASA模型估算了我国1997年植被净第一性生产力及其分布。结果表明：1997年我国植被净第一性生产力为1．95PgC,约是世界陆地植被年净第一性生产力的4．0％;我国植被净第一性生产力的主要分布趋势是从东南沿海向西北逐渐减小,其中海南岛南部、云南西南部、青藏高原东南部的热带雨林和季雨林地区植被年净第一性生产力最大,达900gC.m^2.a^-1以上,而西部塔克拉玛干沙漠地区植被年净第一性生产力最小,不足10gC.m^-2.a^-1。     

利用CASA模型模拟西南喀斯特植被净第一性生产力

基于SPOT NDVI遥感数据并结合数字高程模型、气象数据和植被参数,利用实测植被生产力计算和修正最大光能利用率,通过改进CASA过程模型,本文估算了中国西南喀斯特地区1999—2003年的植被净第一性生产力（NPP）。结果表明：1）改进后的CASA模型模拟的植被NPP与实测值相关性显著,可较好用于西南喀斯特植被的NPP估算;2）西南8省市区1999—2000年喀斯特和非喀斯特植被的NPP有轻度增加,但空间变化不显著,2001年低值区范围增加,2002年NPP高值区的范围明显扩大,随后在2003年又降低,但仍高于2001年;3）5年间西南喀斯特地区年NPP的变化范围是381.7—439.9 gC m-2 yr-1,平均值为402.34 gC m-2 yr-1,逐年NPP波动中呈现总体增长趋势,平均增加值为9.93 gC m-2 yr-1,5年总增加量为11TgC,但非喀斯特地区的年NPP平均值和增加值都大于喀斯特地区;4）5年间喀斯特地区的热带森林、亚热带森林、灌丛和草地的逐年NPP均小于非喀斯特地区,温带森林和农业植被则相反;这6种典型植被年NPP均呈增加趋势,热带森林的增加值最大,草地最小,非喀斯特地区植被NPP的增长趋势相似,但每种植被的年NPP增加值均大于喀斯特地区。西南喀斯特地区植被NPP的时空变化与气温、降水和太阳辐射的变化有关,而喀斯特植被NPP低于非喀斯特地区,则主要由喀斯特地区水分匮缺、土壤贫瘠等恶劣条件而抑制植物生长造成的。     

毛乌素沙地海流兔河流域植被净初级生产力估算

采用CASA(Carnegie-Ames-Stanford Approach)模型,结合TERRA MODIS卫星数据和气象数据,对毛乌素沙地海流兔河流域2015年各月的植被净初级生产力(NPP)进行估算,并对植被NPP月平均值的时空分布规律及其与气象因子和地下水位埋深的关系进行了分析.结果表明:毛乌素沙地海流兔河流域2015年植被NPP总量为2.88×1011 g,生长季(4月份至10月份)的植被NPP总量达2.81×1011 g,占全年植被NPP总量的97.57%.随着时间推移,植被NPP月平均值和归一化差分植被指数(NDVI)月平均值呈"缓慢增加—急剧增加—急剧下降"的变化趋势.植被NPP月平均值季节变化明显,春季、夏季、秋季和冬季植被NPP月平均值之和分别为20.55、69.39、20.46和0.48 g·m-2.从空间分布上看,中部河谷和滩地的植被NPP月平均值总体上高于东南部、西部和西北部等沙丘荒漠区.月平均气温对植被NPP月平均值变化的影响最大,其次为平均实际日蒸散发量和地表月太阳辐射.植被NPP月平均值随着地下水位埋深的增加而减小,最大值出现在地下水位埋深1~2 m之间.上述研究结果显示:采用CASA模型可以较好地估算毛乌素沙地海流兔河流域植被NPP值,月平均气温和地下水位埋深对该流域植被NPP值的影响较大.     

广州市十种森林生态系统的碳循环

为了探讨南亚热带森林生态系统碳循环的规律,在广泛收集资料和试验数据的基础上,对广州10种森林生态系统的碳循环进行研究.结果表明：10种森林生态系统的碳密度在108.35～151.85 t C·hm^-2,其中乔木层碳密度在10.85～48.86 t C·hm^-2,0～60 cm土壤层在87.74～99.01 t C·hm^-2,均低于全国平均水平;从大气流向植被层的碳流量为4.41～9.15 t C·hm^-2·a^-1,植被层流向土壤层的碳流量为0.74～2.06 t C·hm^-2·a^-1,土壤层流向大气层的碳流量为3.94～5.42 t C·hm^-2·a^-1,即系统从大气净吸收碳在0.47～4.97 t C·hm^-2·a^-1之间.各种林分的净系统生产力不同,阔叶林大于针叶林,混交林大于纯林,天然次生林大于人工林.