The Seasonal Pattern of Stem Diameter Growth and Litter Accumulation Based on Meteorological Conditions in <i>Pinus </i><i>merkusii</i> Plantation Forest on Sulawesi Island, Indonesia

This study focused on stem diameter growth and litter accumulation as one possible approach to understanding tree productivity and growth under meteorological conditions. We selected a 62-year-old pine (Pinus merkusii) planted forest located on Sulawesi Island, Indonesia, to be studied for two years. Dendrometer bands were set up on nine individuals to track stem diameter growth, and litter traps were installed at eight locations to measure the amount of litter. Meteorological data, including air temperature, precipitation, air humidity, and solar radiation, were recorded using instruments positioned near the pine stand, while soil moisture was measured at four different depths. Results showed that the stem diameter did not change during the dry season but increased during the wet season. The increase in stem diameter varied among individuals, but the increase stopped at the end of the wet season and the beginning of the dry season. The observed increase in stem diameter may have included short-term water expansion of the tree body, which was considered to disappear during the dry season and could be interpreted as hypertrophic growth of the stem. Litter production, which included branches and cones, was 8.45 Mg∙ha−1∙y−1. By the end of the eight-month dry season, the monthly litter amount increased to approximately 1.5 times the average annual production. The monthly increase in stem diameter showed a significant positive correlation with monthly precipitation. The monthly litter volume had a significant positive correlation with monthly maximum air temperature and a significant negative correlation with monthly average soil moisture in the deeper layers. This study suggests that in areas with distinct dry and wet seasons, P. merkusii trees had greater growth in assimilative organs such as stems during the wet season, while they minimized water loss through transpiration by shedding more litter at the end of the dry seasons.