Findings from long‐term monitoring studies of Micronesian mangrove forests with special reference to carbon sequestration and sea‐level rise

Abstract

AbstractThis paper summarizes the forest dynamics and carbon sequestration abilities of, as well as the influences of sea‐level rise on, Micronesian mangrove forests as revealed from long‐term studies (more than 25 years). Monitoring surveys of the permanent plots in the area's major mangrove communities revealed that the tree density decreased, while aboveground biomass increased. However, in the Rhizophora stylosa community characterized by densely developed stilt roots, the aboveground biomass temporarily decreased due to a decrease in old stilt roots, but it increased again by generating a large amount of new stilt roots. The highest aboveground biomass was estimated to be 895 Mg ha−1, which is the highest value of all the existing ground survey data from the tropics. Mangrove peat was deposited in the entire mangrove area, but its thickness differed according to the forest community, which indicated that the belowground stored carbon also differed depending on the community. In recent years, a rise in sea level exceeding 5 mm year−1 was observed in this region, and surface erosion occurred in the Bruguiera gymnorrhiza and Sonneratia alba communities. On the other hand, in the R. stylosa and Rhizophora apiculata communities, the ground level rose due to the accumulation of mangrove peat. The temporal decrease in old stilt roots and the accelerated increase in new stilt roots observed in the R. stylosa community may also be an effect of sea‐level rise. Long‐term monitoring surveys in mangrove forests are thus effective in quickly catching the effects of sea‐level rise.