[M-IS03] Wetland ecosystems under pressure, impacts on the environment and social activities

[MIS03-P01] Bulk density and specific gravities of living and dead mangrove roots - Determining the substratum formation ability as a root volume based on fine root production.

*Kenji Ono¹, Kiyoshi Fujimoto², Keita Furukawa³, Shin Watanabe⁴, Kodai Hasada⁵, Yumi Kihara⁶ (1.Forestry and Forest Products Research Institute, 2.Nanzan University, 3.Association for shore environment creation, 4.Ryukyu University, 5.Nara University, 6.E-konzal)

Keywords:mangrove, sea level rise, fine root productivity, substratum formation

Sea-level rise with global warming has already caused surface erosion and other impacts in some mangrove stands of the Pacific islands. Since mangroves can only grow in the upper part of intertidal zone, their survival is threatened if the rate of sea-level rise exceeds their substratum formation rate and sediment accumulation rate as their growing bases. Mangroves have high fine-root production capacity, so it reported that some mangrove species use their high fine-root productivity to produce and accumulate mangrove peat on their belowground substratum to raise ground level and maintain their own habitat against sea-level rise. In this study, as a preliminary step to determine the peat-forming capacity of mangroves due to fine-root production in terms of volume per area, we attempted to measure the bulk density and the specific gravity of living and dead mangrove roots on Iriomote Island, Japan, and on Pohnpei Island, Federated States of Micronesia. The bulk density of mangrove roots generally differed depending on whether the roots were alive or dead, and was significantly higher for living roots (<0.5 mmφ) and dead roots than for other diameter classes. Based on the measured bulk density of mangrove roots in this study and the fine root production rates in our previous studies, the annual substratum formation capacity of mangrove fine roots was estimated to be approximately 0.6-5.2 mm/year/30 cm depth on Pohnpei Island, and 0.5-1.1 mm/year/30 cm depth on Iriomote Island. The global average sea level rise rate is 3.7 mm/year for 2006-18 (IPCC 2021). The rate of sea-level rise in recent years is reaching a level that could affect the survival of mangrove forests.