Growth of Tamanu ( <i>Calophyllum Inophyllum</i> L.) Seedlings in Peat Soil Is Inhibited by One Week of Flooding

Tamanu ( Calophyllum inophyllum L.) has attracted increasing attention as a promising species for tropical peatland restoration in Southeast Asia. For successful restoration, it needs to survive and grow under flooded conditions, and flooding is a key factor affecting the performance of seedlings planted in tropical peatlands. To evaluate the restoration potential of tamanu, we examined the survival rate, plant height, number of leaves, root collar diameter, dry biomass and leaf area of tamanu seedlings grown in peat soil under different flooding durations, using a randomised block design. An experiment was conducted in a water tank using five flooding duration treatments and 12 tree-level replicates per treatment: F0 (non-flooding as control); F3 (3 days flooding); F5 (5 days flooding); F7 (7 days flooding); and F11 (11 days flooding). All seedlings survived across all treatments; however, their growth was inhibited as the flooding duration increased, particularly beyond one week. Of the performance indicators evaluated, number of leaves appeared to be the most sensitive to flooding stress, indicating its potential as an early indicator of plant stress. This study confirmed that even short-term flooding can cause significant growth reduction in C. inophyllum seedlings planted in tropical peat soils. Further studies are needed to reflect a wider range of flooding durations and water levels that may occur in tropical peatlands in the future.