Forest Hydrological Studies to Improve Water Management in Marine Lowlands in Palembang, Indonesia

Marine lowlands are a challenging environment for forestry plantation in Indonesia, due to poor drainage, low soil pH and frequent flooding (caused by the almost completely flat area). In the beginning of 2017, OKI pulp and paper mill Ltd (machinery from Finland) initiated its production in the Palembang region in south-west Sumatra (Indonesia), where the wood for pulp is also produced. The area meant to provide wood to the mill will not be sufficient if the land and forest production deteriorates due to the observed potential problems with marine clays, such as land subsidence, floods and acidity. To meet the demand for wood, Sinar Mas forestry Ltd in the Palembang region has initiated a study to improve water and land management in order to maintain long term forest productivity. This doctoral thesis aims to study the hydrology and water management of the Eucalyptus pellita forest in these lowland areas. The first study focused on the water requirements of Eucalyptus pellita during initial growth (meso scale). The results showed that the average Kc value for E. pellita at age 40–142 days is 0.79, which exceeds that reported for E. grandis. Thus, the recommended irrigation requirement varies depending on precipitation, from 70 mL/plant/day with no rainfall to zero when there is precipitation of >30 mm/day. The second study was carried out to explore the functioning of the existing drainage system adjacent to a flooding river (catchment scale of water management). The study shows how the river capacity controls drainage. The second study showed the tidal affects in the river and the adjacent drainage area with Acacia plantations. Cleaning of the river had a significant effect on each river monitoring station and increased the discharge and velocity by more than 5 times and reduced the water level by more than 40%. The third study looked at the effect of the water table on growth of E. pellita (field scale). The results of third study showed that the best tree growth over a 12-month period was in WT 40 – 80 cm with mortality around 10%. With WT 0 – 40 cm, the mortality was 50% due to 2 months of flooding when the trees were 2 months old. With a shallow WT range of 0 – 40 cm, the trees had the shortest root depth (about 22 cm). This thesis provides practical information to support sustainable forest management in Indonesian lowlands, while also considering local communities. The framework presented here could be used by operation teams in order to ensure wood for the regional pulp and paper industry in Indonesia.