Water scarcity and oil palm expansion: social views and environmental processes

Abstract

ABSTRACT. Conversions of natural ecosystems, e.g., from rain forests to managed plantations, result in significant changes in the hydrological cycle including periodic water scarcity. In Indonesia, large areas of forest were lost and extensive oil palm plantations were established over the last decades. We conducted a combined social and environmental study in a region of recent land-use change, the Jambi Province on Sumatra. The objective was to derive complementary lines of arguments to provide balanced insights into environmental perceptions and eco-hydrological processes accompanying land-use change. Interviews with villagers highlighted concerns regarding decreasing water levels in wells during dry periods and increasing fluctuations in stream flow between rainy and dry periods. Periodic water scarcity was found to severely impact livelihoods, which increased social polarization. Sap flux measurements on forest trees and oil palms indicate that oil palm plantations use as much water as forests for transpiration. Eddy covariance analyses of evapotranspiration over oil palm point to substantial additional sources of evaporation in oil palm plantations such as the soil and epiphytes. Stream base flow from a catchment dominated by oil palms was lower than from a catchment dominated by rubber plantations; both showed high peaks after rainfall. An estimate of erosion indicated approximately 30 cm of topsoil loss after forest conversion to both oil palm and rubber plantations. Analyses of climatic variables over the last 20 years and of a standardized precipitation evapotranspiration index for the last century suggested that droughts are recurrent in the area, but have not increased in frequency or intensity. Consequently, we assume that conversions of rain forest ecosystems to oil palm plantations lead to a redistribution of precipitated water by runoff, which leads to the reported periodic water scarcity. Our combined social and environmental approach points to significant and thus far neglected eco-hydrological consequences of oil palm expansion.

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

“…Therefore, we measured the water storage capacity of leaf axils along the trunks of four 10-12-year-old oil palm trees with 10 replications per tree. We found that the leaf axils along the trunk can store up to 20 L or 8.4 mm of water (Table 1), which matches previous reports that the leaf axils along oil palm trunks have a high water storage capacity (Merten et al, 2016;Meijide et al, 2017).…”

“…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?…”

Rubber tree transpiration in the lowlands of Sumatra

“…Even though rubber cultivation is increasingly moving to the Asian mainland (Li & Fox, 2012), Indonesia is still the second largest rubber-producing country in the world (FAOSTAT, 2016). In contrast to, for example, the expansion of oil palm plantations, which has been linked with periodical local water scarcity, rainforest transformation to rubber plantations may thus not be as concerning due to relatively low transpiration rates (Merten et al, 2016). It might be relatively low and thus lower than reported in previous studies from the Asian mainland due to a variety of reasons: In Sumatra, rubber plantations are mainly owned by local small holders, which results in a relatively low management intensity.…”

Expansion of oil palm and other cash crops causes an increase of the land surface temperature in the Jambi province in Indonesia

“…The high precipitation in this region in combination with the reduced vegetation cover of bare land and young oil palm plantations impose risks of soil erosion caused by surface run off. Less water infiltration into the soil, thereby decreasing the soil water storage, may lead to low water availability in the dry season Merten et al, 2016). High surface temperatures in combination with low water availability may make the vegetation and the surroundings more vulnerable to fires.…”