作 者 ：王盛萍,张志强*,张建军,朱金兆,郭军庭,唐寅
期 刊 ：生态学报 2010年 30卷 22期 页码：6102~6112
Keywords:GAM, topographic variables, spatial distribution, secondary species,
摘 要 ：研究流域次生植被物种对地形因子的响应规律，识别影响次生植被物种分布的主要地形因子，是流域近自然植被生态恢复和重建的基础。采用ArcGIS空间分析模块和地形分析模块TauDEM，并与统计软件SPLUS2000中的GRASP工具相结合，建立了位于黄土高原残垣沟壑区山西省吉县蔡家川流域次生植被各个物种分布基于地形因子的广义相加模型（GAM）。模型中的地形因子包括：海拔、坡向、坡度、平面曲率、坡位指数（SPI）、地形湿度指数（TWI）、单宽汇水面积（SCA）等。受试者操作特征曲线（ROC）测试中AUC值表明：大部分测试物种（约62%）拟合模型效果较好，且模型较为稳定。总体来看，研究流域次生植被物种分布体现了水分限制的空间分异特征：阴坡各物种分布概率较大，且随海拔升高而减小。影响研究流域次生植被物种空间分布的潜在重要因子为海拔和坡向，而单宽汇水面积（SCA）和地形湿度指数（TWI）虽然是多个物种响应模型的预测因子，但受高一级尺度海拔的影响，SCA与 TWI对物种分布的影响作用较小；坡度影响作用最小。据此，在流域植被恢复和防护林建设目标区选择及立地条件划分时应首先以海拔和坡向为依据，单宽汇水面积（SCA）和地形湿度指数（TWI）则可以作为次一级立地分类依据，而坡度则仅能作为最后一级的分类依据。
Abstract:It is important to study how secondary species responds to topography-induced environmental changes and to identify dominant topographic factors that affect the spatial distribution of secondary species. The basic information is essential for prioritizing ecological restoration area. By using the GRASP utilities of SPLUS2000, we developed the GAM model for each secondary species of Caijiachuan watershed on the basis of the topographic variables that was calculated by using both spatial analysis packages of ArcGIS9.2 and the TauDEM. The topographic indexes included elevation, aspect, slope, plan curvature, slope position index (SPI), wetness index (TWI), and specific catchment area (SCA).The vegetation information for thirteen selected secondary species was extracted from Quickbird imageries. To establish the GAM models, we used 1 to represent the presence of each specific species, and 0 to represent the absence. Generally, a total of 3927 sample points recording both topographic information and the corresponding vegetation information were employed to build the GAM models of the specific species. The results show that most of the established models performed well, with the AUC values being higher than 0.7. Moreover, the models were stable as the AUC values were similar between the validation and the cross-validation test. In spite of the small difference in the form of GAM models between the herbaceous species and shrub species, both elevation and aspect were influential in controlling spatial distributions of the secondary species.The spatial distribution of the secondary species generally follows the spatial pattern of the water availability, showing a higher probability of the occurrence of specific species on the shady slopes and lower elevation area. Due to the effect of large-scale topographic variables such as the elevation, both specific catchment area (SCA) and wetness index (TWI) that reflects micro-scale had less influence on the spatial distribution of the species. Slope was considered as the least importance. We conclude that vegetation restoration in the Loess area should follow the spatial distributions of secondary species and take into account the spatial variability of water availability. According to the potential of the topographic variables in affecting the spatial distribution of vegetation, both elevation and aspect should be considered as the principle factors in identifying the target area for vegetation construction and in site suitability assessment. Both specific catchment area (SCA) and wetness index (TWI) should be considered as the secondary factors, whereas slope should be considered as the last factor.
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