Mitigation options for improving the ecosystem function of water flow regulation in a watershed with rapid expansion of oil palm plantations

Minimum forest cover required for sustainable water flow regulation of a watershed: a case study in Jambi Province, Indonesia

“…In Indonesia, which is currently the largest palm oil producer worldwide, the oil palm plantation area increased from 7000 km 2 in 1990 to 110 000 km 2 in 2015 (Ditjenbun, 2015;Tarigan et al, 2016b), and a further 170 000-200 000 km 2 is projected for future oil palm development (Colchester et al, 2006;Wicke et al, 2011;Afriyanti et al, 2016). This rapid expansion of oil palm plantations has been partly triggered by an increased demand for biofuel production (Mukherjee and Sovacoo, 2014).…”

“…Similarly, rubber plantations have environmental impacts such as reducing the soil infiltration capacity, accelerating soil erosion, increasing stream sediment loads (Ziegler et al, 2009;Tarigan et al, 2016b), and decreasing soil carbon stocks (Ziegler et al, 2011). Furthermore, the conversion of tropical rainforest into oil palm and rubber plantations affects the local hydrological cycle by increasing transpiration (Ziegler et al, 2009;Sterling et al, 2012;Röll et al, 2015;Hardanto et al, 2017), increasing evapotranspiration (ET) , decreasing infiltration (Banabas et al, 2008;Tarigan et al, 2016b), increasing the flooding frequency (Tarigan, 2016a), and decreasing low flow levels (Yusop et al, 2007;Adnan and Atkinson, 2011;Comte et al, 2012;Merten et al, 2016). These climatic impacts that occur due to land use change are expected to be stronger under maritime conditions, such as those in Indonesia, than under continental conditions because 40 % of the global tropical latent heating of the upper troposphere occurs over the maritime continent (Van der Molen et al, 2006).…”

“…The forests in Jambi Province, Indonesia, have been largely transformed into plantations (Drescher et al, 2016), resulting in inhabitants experiencing water shortages during the dry season and a dramatic increase in flooding frequency during the wet season (Merten et al, 2016;Tarigan, 2016a) because plantations promote higher levels of direct runoff than forested lands (Bruijnzeel, 1989(Bruijnzeel, , 2004Tarigan et al, 2016b;Dislich et al, 2017). However, this negative impact of plantation expansion could be minimized by maintaining an adequate proportion of forested land as a watershed, which raises the following question: what is the minimum proportion of forest cover that is required in a watershed to support adequate water flow regulation?…”

“…Functional water flow regulation by a watershed reduces flood peaks by moderating direct runoff (Le Maitre et al, 2014;Ellison et al, 2017) via soil water infiltration through the soil surface and percolation through the soil profile. This vertical movement of water through the soil determines how much water flows as direct runoffs and how much reaches the water table where it is sustained as baseflow or groundwater (Hewlett and Hibbert, 1967;Bruijnzeel, 1990;Le Maitre et al, 2014;Tarigan et al, 2016b). Forest vegetation provides organic matter and habitat for soil organisms, thereby facilitating higher levels of infiltration than other land uses (Hewlett and Hibbert, 1967).…”

“…Meanwhile, Wangpimool et al (2017) found that the expansion of rubber plantations in Thailand between 2002 and 2009 led to an annual reduction of approximately 3 % in the average water yield of the basin, whereas Babel et al (2011) found that the expansion of oil palm plantations in Thailand increased nitrate loading (1.3-51.7 %) in the surface water based on SWAT simulations. Tarigan et al (2016b) also used the SWAT model to simulate the impact of soil and water conservation practices on low flow levels in oil-palm-dominated watersheds in Jambi Province, Indonesia. This study aimed to quantify the minimum proportion of forest cover that is required to allow a watershed to provide adequate ecosystem services.…”