亚热带典型红壤侵蚀区人类活动对植被覆盖度及景观格局的影响

福建省长汀县是中国南方最严重的水土流失区之一,在20世纪80年代初和2000年两次集中治理的推动下,当地生态环境已得到显著改善。基于Landsat系列卫星影像提取长汀县1975—2013年共6期植被覆盖度分布图,分析该区在不同时期植被覆盖度及其空间格局的时空动态,并探讨人类干扰与政策治理对植被覆盖度及景观格局的影响。结果表明:(1)近38年来,长汀县平均植被覆盖度由47.02%(1975)提升至71.47%(2013),在覆盖度结构上逐渐形成以中高和高植被覆盖度占主导的格局;县域中部河田盆地的植被覆盖度由30.83%(1975)提升至60.34%(2013)。(2)在景观格局上,研究期间长汀县极低、低和中低覆盖度斑块平均面积呈波动下降趋势、同时斑块密度增加,而中高、高植被覆盖度区域面积扩大,表明封禁、造林等治理措施导致植被覆盖度较高的区域不断汇聚成片。(3)植被覆盖度的提升在空间上主要集中在海拔600 m和坡度25°以下区域,尤其在海拔400—600 m和坡度5°—15°区域最显著,表明植被的破坏和恢复过程与人类活动的联系密切。(4)空间分析表明,在距离农户居民地边缘1.2 km的范围内,越接近居民地中心的区域植被覆盖度越低、破碎度越大且恢复缓慢,但这种空间差异伴随治理进行正在逐步减弱。总体上看,长汀县生态治理和人类干扰的长期驱动影响,其恢复速度在不断提升。

Spatial and temporal variations in vegetation cover in an eroded region of substropical red soil and its relationship with the impact of human activity

In China, the area of red soil in South China in second only to the loess plateau in terms of area of soil erosion. Changting County in Fujian Province suffers the most serious water and soil erosion where its forest vegetation has been seriously damaged. Intensive large-scale measures to control erosion have been conducted twice in this area during the early 1980s and 2000s. Driven by both of the control measures and social and economic policies, the ecological environment there has been improved significantly and Changting has become a typical example of soil erosion control in China. Based on Landsat satellite images, this study extracted 6 vegetation fraction distribution maps from 1975 to 2013, and analyzed the variation in vegetation cover and landscape pattern during three major periods: 1975-1989, 1989-2000, and 2000-2013. The different terrain characteristics (such as height and slope) and distances from residential areas were also extracted. The results showed the following. (1) The average vegetation coverage of Changting County increased from 47.02% in 1975 to 71.47% in 2013, and the structure of vegetation coverage has been transformed into one dominated by medium-high and high coverage. In the middle of the county, vegetation coverage in the Hetian basin and its vicinity rose from 30.83% in 1975 to 60.34% in 2013. Widely and contiguously distributed forests with low cover in the basin have been replaced by a higher coverage of coniferous forest patches. With the implementation of soil erosion control measures, the vegetation cover of the Hetian basin increased by 8.47% and 13.81%, respectively, during the two intensive control period from 1975 to 1989 and 2000 to 2013. (2) With regards to the landscape pattern of the vegetation cover, the average patch areas of the low, and moderately low level vegetation cover in Changting County showed a trend of falling variability, and patch density increased. In contrast, the area with moderately high and high cover has shown greater volatility. The result showed that ecological intervention leads to the original good vegetation coverage area become more focus, and the poor coverage area distribution gradually broken at the same time. (3) The increase in vegetation coverage has occurred mainly in an area with an elevation lower than 600 m or slope less than 25°, particularly in the area at an altitude ranging from 400 m to 600 m or with a slope ranging from 5°to 15°. It is worth noting that, during 2000-2013, the vegetation coverage increased by more than 10% in the area below 600 m elevation and slope from 5°to 25°, which demonstrates the destruction and restoration of forest vegetation are affected by terrain, and closely related to effects of human activity. (4) Distance to villages reflects the intensity of the impact of human activity on vegetation destruction and restoration. In the area within 50 m from villages, vegetation coverage is the lowest, and it recovers slowest during the periods when the soil erosion control policy was implemented. With increasing distance to villages, the vegetation fraction increased both in value and percentage with time, although this tendency decreases to a stable state in areas more than 1.2 km from village edges. Moreover, human activities also led to increasing fragmentation of the vegetation landscape around residential areas; however, this phenomenon becomes gradually weaker with ecological management under the guidance of the government. Consequently, the vegetation coverage and landscape pattern changes with ecological management and the long-term effects of human activity in this area, with an increasing recovery speed.