Plantation trees are ‘efficient’ users of water
Ground-breaking research by a post-graduate student at NMMU will shed light on the water use efficiency of exotic plantation trees. This research will add important scientific knowledge to the on-going debate around water usage of exotic plantations which has been a highly contentious issue among environmental groups in South Africa for many years.
Zimbabwe-born Tatenda Mapeto did research into the water use efficiency of plantation and indigenous trees for her Masters studies and is now continuing with her PhD with a focus on the water balance in tree production systems.
Under the supervision of Dr Mark Gush (CSIR Hydro sciences group) and Professor Jos Louw (NMMU), Tatenda’s study on water use efficiency seeks to determine how many grams of utilizable timber a tree produces per litre of water that the tree takes up. The focus of the study was on mid-rotation trees growing under a sawn timber regime in the southern Cape.
Although she is not ready to release her data, Tatenda is happy to confirm that exotic plantation species are “very efficient users of water” in terms of utilizable timber produced.
However the general trend of lower water use efficiencies for the indigenous species studied is not a case of high water investment with low timber returns. Rather it is a question of low water use quantities correlating with lower gains in biomass due to lower growth rates.
This implies that opportunities for investing in indigenous tree production systems could lie in other applications such as plantation borders or wetland management. The findings of this study are currently in preparation for scientific publication.
For her PhD Tatenda is essentially modelling the water balance in exotic plantations as well as that of indigenous forest systems in the southern Cape. Integrating surface (evapotranspiration) and groundwater (recharge) components, the study seeks to update the status quo regarding tree production systems, streamflow and groundwater recharge.
This work will provide information and tools that will enable water conservation factors to be taken into account in ongoing efforts to make forestry more sustainable.
The research is focusing on Pinus eliottii and Pinus radiata, and key indigenous species found in the Southern Cape, namely Yellowwood, Stinkwood and Cape Holly.
The research is funded by the Water Research Commission, under the auspices of the Council of Scientific and Industrial Research and NMMU.
Tatenda achieved a Forest Science Diploma from the Zimbabwe College of Forestry in Mutare before continuing her Honours, Masters and now PhD studies at NMMU’s George campus.
*First published in SA Forestry magazine, Feb 2016