Ecohydrological changes after tropical forest conversion to oil palm

Abstract

Given their ability to provide food, raw material and alleviate poverty, oil palm (OP) plantations are driving significant losses of biodiversity-rich tropical forests, fuelling a heated debate on ecosystem degradation and conservation. However, while OP-induced carbon emissions and biodiversity losses have received significant attention, OP water requirements have been marginalized and little is known on the ecohydrological changes (water and surface energy fluxes) occurring from forest clearing to plantation maturity. Numerical simulations supported by field observations from seven sites in Southeast Asia (five OP plantations and two tropical forests) are used here to illustrate the temporal evolution of OP actual evapotranspiration (ET), infiltration/runoff, gross primary productivity (GPP) and surface temperature as well as their changes relative to tropical forests. Model results from large-scale commercial plantations show that young OP plantations decrease ecosystem ET, causing hotter and drier climatic conditions, but mature plantations (age > 8−9 yr) have higher GPP and transpire more water (up to +7.7%) than the forests they have replaced. This is the result of physiological constraints on water use efficiency and the extremely high yield of OP (six to ten times higher than other oil crops). Hence, the land use efficiency of mature OP, i.e. the high productivity per unit of land area, comes at the expense of water consumption in a trade of water for carbon that may jeopardize local water resources. Sequential replanting and herbaceous ground cover can reduce the severity of such ecohydrological changes and support local water/climate regulation.

Dry‐Season Greening and Water Stress in Amazonia: The Role of Modeling Leaf Phenology

“…Trait‐based approaches typically offer a better representation of ecosystem functioning than models grouping plant traits into broad categories (Pappas et al, ). T&C has been successfully applied to simulate water and carbon fluxes in various ecosystems worldwide (Fatichi & Ivanov, ; Fatichi et al, ; Fatichi, Leuzinger, et al, ; Manoli et al, ; Paschalis et al, , ; Pappas et al, ) and is applied here in a revised form to the Amazon rainforests. Consistently with other DGVMs (Restrepo‐Coupe et al, ), in the case of evergreen biomes the original formulation of T&C does not simulate a phenologic cycle of photosynthetic efficiency, which is maintained fixed throughout the year.…”

“…LAI = leaf area index; PAR = photosynthetic active radiation. (Fatichi & Ivanov, 2014;Fatichi et al, 2015;Fatichi, Leuzinger, et al, 2016;Manoli et al, 2018;Paschalis et al, 2015Paschalis et al, , 2016Pappas et al, 2016) and is applied here in a revised form to the Amazon rainforests. Consistently with other DGVMs , in the case of evergreen biomes the original formulation of T&C does not simulate a phenologic cycle of photosynthetic efficiency, which is maintained fixed throughout the year.…”

Covariation of vegetation and climate constrains present and future T/ET variability

“…The statistical analyses for the present climate are based on the model simulation results reported in Fatichi and Pappas (2017). Seventy nine sites spanning diverse climates and biomes, representative of most regions in the world (supporting material-figure S1 is available online at stacks.iop.org/ERL/13/104012/ mmedia), were simulated using the T&C ecohydrological model (Fatichi et al 2012a, 2016a, Paschalis et al 2015, Manoli et al 2018. The model simulates the coupled energy, water and carbon cycles using mechanistic formulations.…”

Reconciling Canopy Interception Parameterization and Rainfall Forcing Frequency in the Community Land Model for Simulating Evapotranspiration of Rainforests and Oil Palm Plantations in Indonesia

“…The mean ET of forests in lowland areas (elevation <100 m) is almost the same as that of all forest areas in Sumatra and Kalimantan. The regional average difference between oil palm and forest is in line with our site comparisons (section ) and an ecohydrological modeling study by Manoli et al () that find increased ET and T in mature industrial oil palm plantations compared to forests in Indonesia. Our literature review finds slightly higher ET in oil palm plantations (3.6 ± 0.8 mm/day) than forests (3.5 ± 0.9 mm/day) in tropical regions within and outside of Indonesia.…”

“…Merten et al (2016) observe no significant difference in soil moisture content (top 0.3 m) under forests and oil palms in our study area due to limited sampling size and high within-plot variability. Manoli et al (2018) find reduced surface runoff and aquifer recharge in multiple mature oil palm sites compared to a reference forest site, whereas Merten et al (2016) and Tarigan et al (2018) observe enhanced surface runoff in oil palm plantations due to reduced infiltration associated with soil compaction by intensive harvest activities. However, these site-level studies do not consider large-scale variations in hydrology driven by mesotopographic and macrotopographic features and watershed characteristics, and they focus on a limited range of plantation age.…”