卧龙地区流域土地覆盖变化及其对大熊猫潜在生境的影响

The land cover changes of watersheds in Wolong and their impacts on Giant Panda potential habitats

土地覆盖变化作为土地利用驱动的显著结果,是人类活动对环境影响的最显著的表现。为了将土地覆盖变化结果用于探讨大熊猫潜在生境与人为活动导致的环境变化之间的关系,利用1∶25万数字高程模型和1∶10万土地覆盖分类数据(1990年,2000年两期),采用流域时空对比和景观格局分析的手段,对卧龙地区两流域土地覆盖变化及大熊猫潜在生境的景观格局变化进行了对比研究,结果表明:①10a间,寿溪流域土地覆盖年变化率(0.33%)低于渔子溪流域(1.02%),且两流域土地覆盖类型的变化趋势有所不同。主要表现为:在寿溪流域,主要土地覆盖类型的斑块均表现出破碎化的趋势,且森林和灌丛的斑块破碎化趋势更显著;而在渔子溪流域,仅是与人类活动相关的草地、农田斑块破碎化加剧,而森林和灌丛的平均斑块大小反而增加了。②两流域大熊猫潜在生境的景观格局变化趋势有所不同。在渔子溪流域,大熊猫潜在生境的景观多样性指数、均匀度指数、破碎度和森林景观形状指数均高于寿溪流域。而与渔子溪全流域相比,该地区大熊猫潜在生境的森林平均斑块大小较小,并且近十年,在渔子溪流域,大熊猫潜在生境景观的森林面积比重及斑块大小的减少,森林景观形状指数的增加等变化趋势与全流域的相反,间接反映出渔子溪流域的大熊猫潜在生境所受的人类活动的压力更大。③两流域分级集水区的大熊猫潜在生境比重分布与居民点密度分布存在空间上的分异。利用缓冲区分析表明,在渔子溪流域,大熊猫潜在生境与居民点范围的重叠更为严重,约57.7%的人类活动范围处于与大熊猫潜在生境重叠的区域。据此推断,大熊猫潜在生境在流域中的分布与人类活动空间上的交错关系是导致近十年渔子溪流域大熊猫生境受到严重干扰的重要原因。

Land cover changes as a result of land uses represent the most significant impacts of human activities. To reveal the relationship between the changes of Giant Panda babitats and environmental alterations resulted from human activities at a watershed scale, the digital elevation model of 1：250000 was used to select two watersheds （Shouxi and Yuzixi） and Giant Panda potential habitats in Wolong area. According to the water-gathering feature, the two watersheds were divided into one to four ranks of gathering grounds. In addition, land cover databases of 1 ： 100000 of 1990 and 2000 were used to conduct temporal and spatial landscape pattern analyses. Overall, the results showed that the greatest changes of land cover for both watersheds occurred in the dense human residential area in the last decade. However, the changing trends in the two watersheds were different, Land cover change percentage in Shouxi watershed was lower than that of Yuzixi （0.33% and 1.02%, respectively）. Moreover, in the Sheaxi watershed, the mean patch sizes of main land cover types, such as farmland, shrub, grassland and forest, decreased. On the other hand, in the Yuzixi watershed, the mean patch sizes decreased in farmland and grassland, while that increased in forest and shrub. The landscape pattern indices of the Panda potential habitats between the two watersheds showed different patterns as well. For the diversity index, evenness index, fragmentation degree of landscape and shape index of forest, the Yuzixi watershed was higher than the Shouxi watershed. The mean forest patch size of the potential habitats in the Yuzixi watershed was smaller than that of the whole watershed. Furthermore, in the Yuzixi watershed, the change trends of area proportion, patch size of forest and forest landscape shape index of Panda potential habitats were opposite to those of the whole watershed. This suggests that the landscape of Panda potential habitats in Yuzixi watershed might be disturbed by human activities more seriously than in the Shouxi watershed. The statistics of proportions of Panda potential habitats and human residential area density on the four gathering grounds showed that spatial separation existed in the distributions of Panda potential habitats and human residential area. The overlapping of these two factors was more serious in the Yuzixi watershed. The area proportion of buffer zone of human residential places overlapping with Panda＇s potential habitat is about 57.7% in the Yuzixi watershed, but only 5.2% in the Shouxi watershed. Therefore, it has been suggested that the spatial overlap of the distributions of Panda potential habitats and human activity ranges may be an important reason resulting in the degradation of Giant Panda habitats in the past decade.