基于TM影像的白云岩与石灰岩上喀斯特植被时空变化差异研究

喀斯特土壤主要由白云岩和石灰岩风化而来,植被生长及其分布究竟怎样响应这一特殊地质背景?以人为干扰影响较小的喀斯特自然保护区为研究对象,采用监督分类法对1990年和2011年两期TM影像进行植被分类,并利用景观格局分析方法研究两种岩性上植被变化差异。结果表明,1990年和2011年研究区内两种母岩上均以乔木林和乔灌为主,草灌和草丛分布少,白云岩上乔木林的面积比例大于石灰岩上的比例,而草灌和草丛小于石灰岩上的比例;近20年来白云岩与石灰岩上草丛、草灌、灌丛和乔灌均以正向演替为主,但白云岩上正向演替比例大于石灰岩上的比例;两种岩性上植被斑块连接性均增强、破碎程度均降低,白云岩上植被斑块的破碎化程度和多样性指数较石灰岩上低,内部连接性强。由此可见,喀斯特白云岩较石灰岩有利于草丛、草灌的自然恢复,岩性引起的水土资源配置和养分地球化学循环过程差异制约着喀斯特地区植被的时空格局。

Spatial and temporal vegetation changes under geological settings of dolomite and limestone based on TM images

Karst topography has high susceptibility to degradation due to human disturbance. During the last decade, much effort has been made to recover the vegetation in the region of southwest China characterized by karst topography. However, the recovery varies regionally. This study was aimed to assess the impacts of bedrocks on vegetation dynamics. Soil in the karst region of southwest China was mainly derived from limestone and dolomite bedrocks. A natural reserve was selected as the study area to examine the geological control on vegetation change. We classified the Landsat TM5 data recorded in 1990 and 2011 using a supervised classification method for stages of succession of natural vegetation and image characteristics of karst region. We then analyzed spatial patterns to identify the differences in vegetation change rate and direction for two different rock types (limestone and dolomite). In both cases, results showed that the vegetation mainly consisted of forest and tree-shrub mixture in 1990 and 2011. Compared to forest and tree-shrub mixture, the areas covered by grass-shrub mixture and grass were small. The forest cover over dolomite bedrock was higher than that over limestone bedrock, while the grass and grass-shrub mixture covers over dolomite bedrock were lower than those over limestone bedrock. Steady forest cover existed in the areas with limestone and dolomite bedrock regions. In regions characterized by dolomite bedrock, the steady forest cover was higher than that in limestone, and the tree-shrub mixture cover increased slowly in both regions. Grass, grass-shrub mixture, shrub, and tree-shrub mixture vegetation-types were all in the period of positive succession and the percentages of positive succession of these four cases over dolomitic bedrock were higher than that in the areas with limestone bedrock. The connectivity was increased and the fragmentation was decreased in areas with limestone and dolomite bedrock. While, the level of fragmentation and diversity was lower in case of dolomite bedrock than that in case of limestone bedrock. The underlying mechanisms include varying soil depth, soil chemical properties, hydrology, etc. between the two types of bedrocks. The results implied that for grass-shrub mixture and shrub, natural recovery may be more suitable in areas with dolomite bedrock than in areas with limestone bedrock.