Ecohydrological changes after tropical forest conversion to oil palm

Gabriele Manoli,Simone Fatichi,Jaboury Ghazoul,Ana Meijide,Alexander Knohl,Yoshiko Kosugi,Neil Huth,Paolo Burlando

doi:10.1088/1748-9326/aac54e

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.

Highlights

Oil palm (Elaeis guineensis) plantations expansion has boomed over the last decades (global planted area increased from 6–16 Mha between 1990 and 2010 (Pirker et al 2016)), mostly in Southeast Asia (Koh et al 2011, Dislich et al 2017) at the expense of biodiversityrich tropical forests (Koh et al 2011, Pirker et al 2016, Vijay et al 2016) and other land-covers such as pastures or pre-existing plantations (Gaveau et al 2016, Austin et al 2017, Furumo and Aide 2017)
Due to high fruit productivity oil palm (OP) plantations have been documented to uptake more carbon than tropical forests (Kotowska et al 2015) but carbon storage in OP biomass is insufficient to balance the carbon losses caused by forest clearing (Kotowska et al 2015, Dislich et al 2017) and, over a 30 year period, OP establishment might result in carbon emissions from 702 t CO2 ha−1 to 3452 t CO2 ha−1 depending on the soil type (Fargione et al 2008, Dislich et al 2017)
With respect to OP monocultures (typical of large-scale plantations, i.e. 3000–20000 ha (Dislich et al 2017)), we show (i) how much ecosystem ET and gross primary productivity (GPP) change when a representative tropical forest is replaced by an OP plantation; (ii) we quantify how these changes are modified by plantation age; (iii) and we demonstrate the role of OP understory vegetation

Summary

Introduction

Oil palm (Elaeis guineensis) plantations expansion has boomed over the last decades (global planted area increased from 6–16 Mha between 1990 and 2010 (Pirker et al 2016)), mostly in Southeast Asia (Koh et al 2011, Dislich et al 2017) at the expense of biodiversityrich tropical forests (Koh et al 2011, Pirker et al 2016, Vijay et al 2016) and other land-covers such as pastures or pre-existing plantations (Gaveau et al 2016, Austin et al 2017, Furumo and Aide 2017). OP expansion is projected to increase accross the entire tropics where an additional 19 Mha of suitable land are potentially available for OP cultivation (Pirker et al 2016). Such an ability to provide food and raw material (Dislich et al 2017), while contributing to rural development and poverty alleviation (Sayer et al 2012), has driven deforestation and generated negative environmetal impacts which earned OP the label of ‘world’s most hated crop’ (Yan 2017). There is a knowledge gap on the magnitude of such ecohydrological changes and their variations accross plantation ages (Dislich et al 2017)

Methods

Results

Discussion

Conclusion