Exploring the effects of biophysical parameters on the spatial pattern of rare cold damage to mangrove forests

Abstract

In recognition of the role of mangrove forests as natural barriers and bio-shields in protecting coastal population and property in the aftermath of the 2004 Indian Ocean tsunami disaster, many Asian countries have launched various projects to restore and conserve mangrove trees. The growth and vitality condition of mangroves may be negatively influenced by various anthropogenic and natural disturbances and stresses, such as cold weather events. This paper represents the first attempt to map the cold damage to mangroves in the tropical zone of Southern China using high resolution multispectral satellite imagery. In this study, the spatial distribution of severity level of cold damage to mangroves imposed by a rare blizzard in Southern China during early 2008 has been mapped and analyzed using IKONOS image. An object-oriented classification applied to the images achieved an overall accuracy of 90.9% for classifying mangroves into three categories: undamaged, damaged, and dead. Of the total 287.30ha of mapped mangroves, approximately 51.1% were damaged or died due to the cold stress of the blizzard. These results have been verified by more recent WorldView-II images. Furthermore, we explored the associations between the cold damage severity level of mangroves and climate and landscape factors, including elevation, surface slope, aspect, wind direction and velocity, wind shadow effect, and tree height. The surface topographical variables are derived from the ASTER Global DEM. The analysis results suggest that wind direction, terrain topography, and proximity to ocean are important local environmental factors controlling the vulnerability of mangroves to cold damage. Most damaged mangroves were located near the open sea, as a result of a possible edge exposure effect. The damage to the mangroves on the leeward side of a hill was also minimal. Such knowledge of climate and landscape controls can offer insight on how to better restore and protect the mangrove forest in the future.