人工林与天然林破碎化过程差异对比——以美国华盛顿州和密西西比州为例

森林损失和破碎化一直是国际社会普遍关注的重大环境问题之一。根据Forman景观变化包括穿孔、分割、破碎化、收缩和消失5种空间过程的理论,利用ArcGIS Modeler建立森林破碎化过程模型用以明确描述森林景观破碎化的空间过程和生态进程。基于NLCD2001、2006、2011 3期数据,以美国华盛顿州和密西西比州为研究区,利用森林破碎化过程模型,将森林损失斑块分为4种破碎化过程(分割类型因其线状特征被归入破碎化类型),对比分析天然林和人工林的破碎化过程在时空上的差异性。研究表明天然林破碎化斑块多分布于城市/森林、耕地/森林、以及灌木/森林的交界处,而人工林破碎化斑块分布格局较为零散;天然林中破碎化斑块和收缩斑块大多发生在上阶段收缩、破碎化以及穿孔斑块的边缘,而人工林中4种空间过程的承接关系不像天然林那么明显,但两者整体上都呈现相似的"收缩-消失-穿孔/破碎化"变化规律,主要表现为收缩类型占主导然后慢慢消退,穿孔和破碎化逐渐增多占据新的主导。

Differences in fragmentation processes between western natural forests and southeastern forest plantations in the United States: a case study comparing the states Washington and Mississippi State

Forest loss and fragmentation have long been one of the most vital concerns of the international community. Landscape fragmentation includes five different spatially explicit processes:perforation, dissection, subdivision, shrinkage, and attrition. Following this theory, a forest fragmentation process model that can detect these spatially explicit processes, as well as the ecological consequences of forest landscape fragmentation, was developed using ArcGIS Modeler. Using the National Land Cover Database (years 2001, 2006, and 2011), the forest fragmentation process model was applied to Washington and Mississippi in the USA. Deforested patches were quantified and categorized into one of four fragmentation processes, by merging the dissection spatial process into the subdivision spatial process (because of its principal linear feature). Furthermore, the spatio-temporal differences in fragmentation pattern between natural forests and plantations were compared. For natural forests, forest fragmentation mainly occurred in the urban/forest, cultivated/forest, and shrubland/forest interfaces, whereas the pattern of deforested plantation patches dispersed sparsely and irregularly throughout the region. The subdivision and shrinkage patches in natural forests usually followed the perforation, subdivision, and shrinkage patches of the previous period. In contrast, for the plantations, the spatial transition relationships of the four fragmentation processes were not as apparent as for the natural forests. Nonetheless, for both natural forests and plantations, the overall temporal fragmentation pattern tended to have a similar "shrinkage-attrition-perforation/subdivision" tendency. This tendency was characterized by an early shrinkage dominance, followed by its gradual disappearance. Furthermore, perforation and subdivision components increased gradually, and a new dominance was established accordingly.