利用CASA模型模拟西南喀斯特植被净第一性生产力

Modeling changes of net primary productivity of karst vegetation in southwestern China using the CASA model

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,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)5a间西南喀斯特地区年NPP的变化范围是381.7—439.9 gC m-2 a-1,平均值为402.34 gC m-2 a-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 a-1,5a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)5a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。

Modeling large-scale net primary productivity（NPP） using remote sensing data and ecosystems model is a great challenge of global change study.The processes-based model of Carnegie-Ames-Stanford Approach（CASA） has been widely used in regional and global NPP estimates.However applying this model to specific region with harsh topography such as the karst terrain is few reported because of the difficulty in accurately estimating the maximum Light Use Efficiency（LUE）.Estimating precisely the karst vegetation NPP is a foundation of rocky-desertified ecosystem restoration in harsh karst habitats.In this study,annual NPP from 1999 to 2003 was simulated using the CASA model driven by SPOT Normalized Difference Vegetation Index（NDVI） at 1km spatial resolution,digital elevation model（DEM）,climate variables and vegetation-based parameters.The CASA model was improved by calculating the maximum LUE for 19 vegetation types based on the field observations of NPP.Results showed that（1） the simulated NPP by the improved CASA model has significant relationship with the observed NPP.This model could be better used in estimating NPP of karst vegetation in SW China.（2） From 1999 to 2000 the NPP of both karst and non-karst vegetation increased slightly in SW China,but the spatial change was not significant.The area with lower NPP enlarged in 2001,but the higher NPP area in 2002 enlarged significantly.The NPP decreased in 2003,but the values were still higher than those in 2001.（3） Annual NPP of karst vegetation in SW China ranged from 381.7-439.9 gC m-2 a-1（average 402.34 gC m-2 a-1） during 1999-2003.The annual NPP fluctuated in this period,but there was an overall increase trend with annual increment of 9.93 gC m-2 a-1.The total amount of increment was 11 TgC during those five years.The averaged annual NPP and its increment of non-karst vegetation were all higher than those in karst vegetation.（4） Annual NPP of tropical and subtropical forests,shrub and grassland in karst region during five years are less than those in non-karst region,but the temperate forests and agricultural vegetation have the opposite trend.All of six types of vegetation have increased their NPP both in karst and non-karst regions,along with the highest increment in tropical forest and the lowest one in grassland.The NPP increments of each vegetation type in non-karst region are higher than those in karst region.In general,the spatial-temporal changes of vegetation NPP in SW China are closely related to regional changes of temperature,precipitation and solar radiation.Karst vegetation has lower NPP than non-karst vegetation is mainly due to the water stress and poor soils in harsh karst habitats that restrict plant growth.