象山港滨海湿地互花米草入侵过程遥感监测与评估

互花米草在20世纪70年代后期作为海岸带生态防护工程物种引入我国,由于其超强的繁殖能力,目前已经对我国的滨海湿地生态环境健康与安全造成了严重的威胁,成为生长在中国沿海的一种典型生态入侵植物,引起了相关部门的高度重视。文章选择浙江象山港为重点研究区,通过遥感技术手段,基于2003年,2009年和2014年中分辨率Landsat系列遥感卫星数据,采用空间与光谱特征相结合的综合判读,提出了生境空间环境支持下的植物群落遥感自动识别方法,动态监测了互花米草在象山港的繁衍和入侵过程已经空间格局变化。研究结果表明:过去10年余年,互花米草在象山港呈现指数模型的爆炸性增长。2003年,整个象山港互花米草的分布面积约为590 hm²;2009年其分布面积达到1745 hm²;2014年互花米草在象山港的分布面积超过5715 hm²。2003-1014年10年间互花米草在该区域分布面积翻了近10倍,几乎占据了海岸带所有的泥质海滩,成为象山港滨海湿地区的主导型盐生植被和区域优势种,对附近农田,尤其是淡水水域构成巨大的威胁。而在快速扩张的驱动要素方面,研究认为强劲的自我繁殖性能是互米花草在区域能够快速扩张的主要原因;人类围垦活动促进了这一快速扩张进程。以上研究结论可为区域互花米草的综合治理提供数据支持和遥感监测提供技术参考。

Detecting and assessing Spartina invasion in coastal region of China: A case study in the Xiangshan Bay

Spartina alterniflora is one of exotic plants along the coastal region in China. It was introduced as an important engineering approach to ecological restoration in the later 1970s. However, owing to its good adaptability and strong reproductive capacity, the introduced species is explosively spreading along the coastal region quickly and resulting in a significant impact on the health and safety of coastal wetland ecosystems. It is imperative to quantify the spatial extent and the rate of S. alterniflora sprawl in order to assess its ecological damages and economic impacts. Remote sensing techniques have been used to address these challenges but large unsuccessful due to mixed spectral properties. In this study, a hybrid method was proposed for S. alterniflora detection using medium resolution remote sensing images by integrating both spatial and spectral features of S. alterniflora. The hybrid method consists of two phases:(1) delineation of intertidal zone as the potential area of S. alterniflora distribution and(2) extraction of S. alterniflora fraction distribution with a mixture pixel analysis. The proposed method was tested at the Xiangshan Bay on the east coastal region of Zhejiang Province, China, and mapped the spatial extent of S. alterniflora with Landsat datasets in the 2003, 2009 and 2014. The results showed that, the S. alterniflora has grown exponentially over past 10 years. In 2003, the total area of S. alterniflora was about 590 hm², but quickly reached to 1745 hm² in 2009, and 5715 hm² in 2014. With a rate of approximately 10-folds growth within a decade, the invasive species almost occupied all muddy beaches to become the most dominant coastal salt vegetation in this region. It is believed that the strong biological reproductive capacity was the primary reason for such quick spread and at the same time human reclamation activities were also believed to have facilitated the environmental conditions for S. alterniflora sprawl.