以植被-生境学分类(vegetation-habitat classification system of grassland,VHCS)方法为基础的定性的中国草地分类系统,以及定量的气候-土地-植被综合顺序分类系统(comprehensive and sequential classification system of grassland,CSCS)是我国常用的2大草地分类系统。在实际应用中,因"草原"和"草地"概念的重叠、混淆和交叉,以及定性分类和定量分类的差异,造成了操作上的困扰,研究结果亦不便相互交流。本研究通过2大系统一级单位-"类"的分类指标、名称和属性的对比,分析了2个系统"类"的兼容性,建立了两者间的对应关系,并利用基本同期的CSCS分类图和数字化的中国草地资源图(VHCS),以内蒙古自治区和甘肃省为例,在ArcGIS平台上进行了验证分析。研究结果表明:1)以广义草原或草地概念为基础的CSCS是一个大系统,兼容了以中国为例的VHCS分类系统;2)兼容VHCS的CSCS的类,两者在分类指标、名称和属性方面均能达到统一;3)空间叠置分析表明,若不考虑森林和非地带性类,内蒙古和甘肃区域2个分类系统分类结果的兼容性分别达到61.4%和61.1%;有差异的区域,基本上表现出草地实际调查结果(VHCS)是比原生潜在草地(CSCS)在更恶劣气候条件下的低分类级别的草地类,说明人为干扰已超过了原生草地生态系统的生存阈限,导致草地逆行演替;4)对CSCS与VHCS分类结果的对比分析研究,可科学地揭示人为干扰下草地的演替状态,并明确草地恢复和重建的目标。
本文基于甘肃省2000—2019年归一化植被指数(normalized different vegetation index,NDVI)数据及气象数据,研究了甘肃省草地NDVI时空变化特征及驱动因素。结果表明:近20年,生长季草地NDVI整体水平较低但呈波动上升趋势,增速为0.030·(10a)^(-1),草地NDVI分布呈现东南高西北低的格局;20年间生长季NDVI呈显著增加趋势的面积占甘肃省草地的19.08%,主要分布在陇中黄土高原;甘南高原和祁连山地生长季NDVI保持稳定,其中高寒草甸NDVI整体较高且稳定性较强;生长季草地NDVI受夏季降水量的影响较大;人类活动主要促进了草地NDVI的增长。整体而言,甘肃省草地NDVI呈现增长趋势且稳定性较高,降水量对草地NDVI的影响较强。另外,生态工程也促进了草地NDVI增长,需长期实施。
Rangeland systems play an important role in ecological stabilization and the terrestrial carbon cycle in arid and semiarid regions. However, little is known about the vegetative carbon dynamics and climatic and topog- raphical factors that affect vegetative carbon stock in these rangelands. Our goal was to assess vegetative carbon stock by examining meteorological data in conjunction with NDVI （normalized difference vegetation index） time se- ries datasets from 2001-2012. An improved CASA （Carnegie Ames Stanford Approach） model was then applied to simulate the spatiotemporal dynamic variation of vegetative carbon stock, and analyze its response to climatic and topographical factors. We estimated the vegetative carbon stock of rangeland in Gansu province, China to be 4.4×10^14 gC, increasing linearly at an annual rate of 9.8×10^11 gC. The mean vegetative carbon density of the whole rangeland was 136.5 gC m-2. Vegetative carbon density and total carbon varied temporally and spatially and were highly associated with temperature, precipitation and solar radiation. Vegetative carbon density reached the maximal value on elevation at 2500-3500 m, a slope of 〉30°and easterly aspect. The effect of precipitation, tem- perature and solar radiation on the vegetative carbon density of five rangeland types （desert and salinized meadow, steppe, alpine meadow, shrub and tussock, and marginal grassland in the forest） depends on the acquired quantity of water and heat for rangeland plants at all spatial scales. The results of this study provide new evidence for ex- plaining spatiotemporal heterogeneity in vegetative carbon dynamics and responses to global change for rangeland vegetative carbon stock, and offer a theoretical and practical basis for grassland agriculture management in arid and semiarid regions.
