Leaf Phenology And Trunk Growth Of Avicennia Alba (Blume) Under A Seasonally Fluctuating Saline Environment In The Tropical Monsoon Area Of Eastern Thailand

Mangrove forests are said to be highly productive ecosystems but it is unclear how they maintain high productivity under the fluctuation of saline environment in the tropical monsoon region. A study of phenological aspects linked with the growth of mangrove trees may be a supportive evidence for this. Here, we studied the seasonal variation in leaf phenology and trunk growth of Avicennia alba trees in a tropical monsoon mangrove forest which has clear rainy and dry seasons at Trat Province, eastern Thailand. For the leaf phenology, the number of new and lost leaves was counted by using demographic techniques, and the monthly rates of leaf emergence and loss were calculated from 45 sample shoots from June 2019 to May 2020. In this period, trunk basal-area increments were also recorded monthly by using dendrometer bands. The rate of leaf emergence showed a remarkable seasonal pattern that was high during the rainy season and low during the dry season. The monthly rate of leaf emergence and trunk growth showed a positive relationship, indicating that both the leaf and trunk growth of A. alba responded to the changing water salinity in the soil. However, the leaf loss rate fluctuated throughout the study period. It was considered that the cambial activity of trunk growth associated with new leaf formation stimulates tree growth under the low saline environment during the rainy season in the tropics. We discussed a growth strategy that will benefit mangrove trees growing in the intertidal areas under fluctuated saline environment.