The Current Extent and Historical Expansion of Mangroves in the Kuantu Nature Reserve, North Taiwan

摘要

The Kandelia candel (L.) Druce mangrove forest in the Kuantu Nature Reserve, North Taiwan, has experienced rapid expansion since 1978. This study assesses the current extent and historical expansion of the mangroves by means of aerial photograph interpretation. An analysis of a time series of aerial photographs, covering the period from 1978 to 2012, has revealed major changes in the distribution of mangroves in relation to the geomorphic changes in the Kuantu Nature Reserve. The results indicate that the area-increasing rate was highest (2.27 ha/y) during the 1986-94 period, meaning the most rapid encroachment of mangroves into the habitats of Cyperus and Phragmites saltmarshes. Based on the Shannon diversity index t test, with the encroachment of Kandelia, the landscape composition in the Kuantu Nature Reserve has been dominated by the mangrove swamp of Kandelia. The geomorphic changes in the area of accretion and erosion were derived from the 0-m contour in the 1:5000 topographic maps in 1978, 1986, 1994, and 2005. Based on a review of related literature, the possible driving forces of geomorphic changes are explained by human impacts (e.g., land subsidence because of the overpumping of groundwater and collapse triggered by sand pumping) and natural forces (e.g., increased accretion induced by mangroves and headward expansion of tidal creek and typhoon-induced erosion). The complicated interplay between vegetation and landform in the Kuantu Nature Reserve is discussed from the viewpoint of biogeomorphic succession. Similar mangrove expansion cases are also examined.