Hydrological Tolerance of Two Restoration Tree Seedlings in Tropical Peatlands under Different Water-table Levels and Inundation Durations

Restoration species planted in degraded tropical peatlands must be able to survive and grow under various hydrological conditions caused by wet and dry seasons. This study evaluated the hydrological tolerance of two species through water tank experiments simulating different water-table levels (ranging from aboveground water-level to groundwater level) and inundation durations in tropical peatlands. Seedlings of the restoration species, Tamanu ( Calophyllum inophyllum ) and Malapari ( Pongamia pinnata ), were grown in peat soil under six water-table levels (drained control, − 15, − 5, +0, +5, +15 cm from the soil surface) and three inundation durations (one-, three-, five-month treatment). The results showed that (1) Tamanu survived across all treatments, while Malapari’s survival rate declined significantly with increasing water-table levels and prolonged inundation. (2) In Tamanu, the growth of plant height, leaf number, and root collar diameter was inhibited under aboveground water-levels from three-month treatment. In contrast, Malapari showed suppressed growth of these traits under aboveground water-levels from one-month treatment, indicating a more sensitive response even at shorter inundation and lower aboveground water-levels. These findings indicate that Tamanu has higher hydrological tolerance than Malapari, which might be due to interspecific differences in the development of morphological adaptive traits (i.e. hypertrophied lenticels and adventitious roots) under flooded conditions. Considering tropical peatlands where inundation lasting longer than one month occurs frequently, Malapari appears unsuitable for restoration purposes. Tamanu can be considered viable, though it requires management to prevent aboveground water-level of 15 cm depth from lasting more than three months during the initial establishment phase.