Rapid Sea Level Rise and Mangrove Habitat

为了阐明红树林泥炭的积累过程与海平面变化的关系，对密克罗尼西亚的波恩佩岛和科斯雷岛以及菲律宾的宿务岛和保霍尔岛的红树林及其生境进行了研究。密克罗尼西亚的泥炭生境有两种类型：一种是厚约30-50 cm的泥炭薄层，另一种是厚达2 m的泥炭薄层。前者支持以Sonneratia alba为主的红树林，后者支持以木果属（Xylocarpus granatum）为特征的红树林。红树林泥炭的堆积局限于与潮间带的一部分相对应的范围，因为红树林生境的地平面本身局限于这一范围。因此，海平面必须上升越来越高，或土地的水平必须下降越来越低，这样厚的泥炭层的发展为2米。事实上，根据地貌和C-14年代的证据，海平面在1800-2000年B. P.时比现在低2 m左右，然后上升到现在的水平，根据我们的研究资料计算的泥炭堆积速率约为2 mm/a。该值并不一定表示红树林生境维持能力的极限，因为它是数百年或数千年的平均值，可能包括短期内的一些更大的值。至少，一片红树林有能力维持自己的栖息地，抵御海平面以每年2毫米的速度上升。

Mangrove forests and their habitats were studied on Pohnpei and Kosrae Islands in Micronesia and Cebu and Bohol Islands in the Philippines, to clarify the accumulation process of mangrove peat in relation to sea-level changes. There are two types of peaty habitat in Micronesia : one with thin peat layr about 30-50 cm thick and the other with thick peat layr as thick as 2 m. The former supports a mangrove forest dominated by Sonneratia alba and the latter another mangrove forest characterized by Xylocarpus granatum. The accumulation of mangrove peat is limited to a range corresponding to a part of the intertidal zone because the ground level of mangrove habitats is itself restricted to this range. Consequently, the sea level must rise higher and higher or the level of the land must fall lower and lower for the development of such a thick peat layr as 2 m. In fact, according to the evidences of landforms and C-14 dates, sea level was at the level about 2 m below present one about 1800-2000 yr B.P.Then, it rose to the present level.The rate of peat accumulation calculated from information obtained from our research was about 2 mm per year. This value does not necessarily indicate the limit of habitat maintenance capability of mangrove forests because it is the average for hundreds or thousands of years and some bigger values within a short period might be included. At least, a mangrove forest is capable of maintaining its own habitat against a sea level rise as rapid as 2 mm per year.