One of the functions of plants in an ecosystem is to preserve water. Through the evapotranspiration mechanism, the plants evaporate water into the atmosphere, which will in turn descend to the Earth as rainfall. Moreover, the plant also preserves soil and water through various mechanisms such as holding a water supply in the topsoil layer, protecting soil from direct rainfall and maintain air humidity in a micro climate.
If oil palm plantations are compared to forests (Table), the two generally have the same function in conservation and hydrology. This is reflected by the evapotranspiration, ground water reserves, deflection of rainfall, infiltration rates and air humidity.
Table: Comparison of water management functions between oil palm plantations and tropical forest
|Indicator||Tropical forest||Oil palm plantations|
|Groundwater reserves up to depth of 200 cm (mm)||59-727||75-739|
|Deflecting rainfall from soil surface (%)||85||87|
|Rate of solum layer infiltration 0-40 cm (ml/cm3/minute)||30-90||10-30|
|Air humidity (%)||90-93||85-90|
Source: Henson (1999), PPKS (2004, 2005)
Since oil palm plantations have a long production cycle of up to 25 years (from planting to replanting), that means they perform conservation and hydrology functions for up to 25 years.