Abstract
One of globally significant ecosystems is seasonally dry tropical forests (SDTFs) that support high biodiversity and contribute substantially to the global carbon cycle. Cambodian SDTFs accounts for approximately 40% of the land area and are strongly influenced by monsoonal climatic variability characterized by pronounced dry and rainy seasons. These seasonal fluctuations regulate key ecological processes, including tree growth, mortality, recruitment, basal area change, and biomass accumulation. However, comprehensive field-based assessments of seasonal forest dynamics across major forest types in Cambodia remain limited. This study aims to examine forest dynamics during dry and rainy seasons in deciduous, semi-evergreen, and evergreen forests at the Khun Ream Forest Research Station, Siem Reap Province, Cambodia.
We used three 1-ha (100 m × 100 m) permanent plots that were established in each forest type within a total study area of 1,888 ha. All trees with diameter at breast height ≥ 5.0 cm were tagged, mapped, and measured at 1.3 m above ground level. Five repeated forest inventories were conducted every six months from April 2023 to April 2025 to capture seasonal variation. Structural assessment revealed clear differences among forest types. The evergreen forest exhibited the highest stem density (1,092 stems ha⁻¹), while the semi-evergreen forest showed the greatest biomass accumulation, with the highest basal area (25.33 m² ha⁻¹) and aboveground biomass (142.80 Mg ha⁻¹). Over the two-year monitoring period, seasonal patterns in forest dynamics were pronounced but varied among forest types. Tree mortality was similar between seasons across all forest types, whereas recruitment rate constantly tended to be higher during the rainy season than during the dry season. Although biomass increment was suppressed during the dry season in all plots, the semi-evergreen forest demonstrated slight but constant biomass gains even in the rainy season. In contrary, the deciduous and evergreen forests showed constant and intermittent biomass loss associated with dry-season stress, respectively. We also found large inter-specific variation in tree growth rates responding to seasons. Especially in top 10 tree species in deciduous forest, tree growth rates largely varied from rainy-season rapid growth to dry-season ~zero‒negative growth.
Overall, climatic seasonality caused seasonal forest dynamics in different ways depending on forest types and tree species.