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

Abstract

This 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.

Comparison of Carbon Storage in Forested and Non-Forested Soils in Tropical Wetlands of Caimanera, Colombia, and Llano, Mexico

“…The vegetation, dead in the form of peat, was deposited in the mangrove, occupying an area in the Caimanera (85.51%) and in the Llano (32.35%). This accumulation of peat has also been observed in some mangroves in Micronesia, where it was attributed to the rise in sea levels [60]. Regarding the sediment, it sequesters carbon according to its texture, which can be silty, clayey, or sandy, each with different sequestering capacities; for instance, silty sediments tend to sequester more carbon if found in greater proportions than others [61].…”

Estimation of total fine root production using continuous inflow methods in tropical mangrove forest on Pohnpei Island, Micronesia: Fine root necromass accumulation is a substantial contributor to blue carbon stocks

“…The latest aboveground biomass (AGB) for each plot was as follows: 329 Mg ha −1 for PR (2019), 494 Mg ha −1 for PS (2016), 559 Mg ha −1 for PC (2017), 895 Mg ha −1 for PE1 (2018), and 591 Mg ha −1 for PE2 (2018) (Fujimoto et al, under‐submission). The average tree diameter and average tree height in each plot except for PE2 increased over time; thus, stand biomass generally increased throughout the tree census period, whereas tree density gradually decreased with each measuring year (Fujimoto et al, under‐submission). For PE2, average tree diameter, height, and stand biomass of some species decreased from 2011 to 2018 due to the occurrence of many fallen trees with relatively large size.…”

“…Table 1 shows the average tree diameter and height, basal area sum (BA), biomass, and tree density in each plot. The latest aboveground biomass (AGB) for each plot was as follows: 329 Mg ha −1 for PR (2019), 494 Mg ha −1 for PS (2016), 559 Mg ha −1 for PC (2017), 895 Mg ha −1 for PE1 (2018), and 591 Mg ha −1 for PE2 (2018) (Fujimoto et al, under‐submission). The average tree diameter and average tree height in each plot except for PE2 increased over time; thus, stand biomass generally increased throughout the tree census period, whereas tree density gradually decreased with each measuring year (Fujimoto et al, under‐submission).…”