Selecting proper tree species for revegetation is important for restoring tropical peatland. Tamanu (Calophyllum inophyllum L.) has been suggested one of the promising native species in Indonesia for the revegetation of tropical peatland; however, there is a lack of understanding of its growth in peat soil with different groundwater levels. We investigated the survival rate, plant height, number of leaves, root collar diameter, and dry biomass of tamanu seedlings grown in peat soil with different groundwater levels using a randomized block design in a water tank. The study involved five groundwater level treatments and 12 tree-level replicates each: M0 (non-groundwater level, control); M1 (−15 cm below the soil surface); M2 (−10 cm); M3 (−5 cm); and M4 (0 cm, soil surface level). The results showed that all tamanu seedlings survived in every treatment. However, their plant height, number of leaves, and root collar diameter growth were significantly inhibited in the highest groundwater level condition (M4, 0 cm) at 81 days after sowing, while their growth in −15 cm of groundwater level (M1) was as good as the growth in the fully drained conditions in M0 (control). This result indicates that the groundwater level should not be higher than −15 cm for the growth of tamanu. Considering that peatlands in Indonesia are assessed to be degraded when the groundwater level is lower than −40 cm, this study suggests that maintaining groundwater levels between −40 cm and −15 cm in peatland is the best condition for rapid growth of early tamanu seedlings while protecting peatlands. Further studies are needed to extend the range of water levels and water treatment duration.
Tag: groundwater level
Rewetting Tropical Peatlands Reduced Net Greenhouse Gas Emissions in Riau Province, Indonesia
Draining deforested tropical peat swamp forests (PSFs) converts greenhouse gas (GHG) sinks to sources and increases the likelihood of fire hazards. Rewetting deforested and drained PSFs before revegetation is expected to reverse this outcome. This study aims to quantify the GHG emissions of deforested PSFs that have been (a) reforested, (b) converted into oil palm, or (c) replanted with rubber. Before rewetting, heterotrophic soil respiration in reforested, oil palm, and rubber plantation areas were 48.91 ± 4.75 Mg CO2 ha−1 yr−1, 54.98 ± 1.53 Mg CO2 ha−1 yr−1, and 67.67 ± 2.13 Mg CO2 ha−1 yr−1, respectively. After rewetting, this decreased substantially by 21%, 36%, and 39%. Conversely, rewetting drained landscapes that used to be methane (CH4) sinks converted them into CH4 sources; almost twice as much methane was emitted after rewetting. Nitrous oxide (N2O) emissions tended to decrease; in nitrogen-rich rubber plantations, N2O emissions halved; in nitrogen-poor reforested areas, emissions reduced by up to a quarter after rewetting. Overall, rewetting reduced the net emissions up to 15.41 Mg CO2-eq ha−1 yr−1 (25%) in reforested, 18.36 Mg CO2-eq ha−1 yr−1 (18%) in oil palm, and 28.87 Mg CO2-eq ha−1 yr−1 (17%) in rubber plantation areas.