The conundrum of South Africa's eucalyptus

This blog has explored the many impacts of deforestation on the water cycle across the African continent. However, I thought it was necessary to explore the possible negative impacts of afforestation notably in South Africa where non-native eucalyptus have become invasive and are discovered to be using up significant amount of freshwater especially when growing on riparian areas and wetlands. 


Eucalyptus trees have been found to 'drink South Africa dry' 


The negative impacts of afforestation

The positive effects that arise from reforesting land are highly dependent on the type of species chosen. The ideal tree species depends on the physical characteristics of the land, which is undergoing reforestation. As Mbow et al, 2014 explain, soil characteristics, land topography, rainfall patterns, agricultural practices and priorities for food security as well as economic development all matter when deciding what tree species to use to reforest deforested land. 

    A classic example of afforestation gone wrong can be observed in South Africa. Eucalyptus trees are widely used worldwide as they are valuable sources of timber, fuelwood, paper and nectar and are thus widely used in plantations and afforestation practices. However, they often becomes invasive and escape cultivations. An assessment done in South Africa by Forsyth et al, 2004 surveyed 82 sites and found all species of eucalyptus to be 'naturalised' but only 2 species to be clearly invasive. This has significant impacts for biodiversity of ecosystems as well as water use especially in riparian areas and wetlands. Certain eucalyptus species in South Africa have been found to be responsible for the loss of 16% of the 1,444 million cubic metres of water resources lost to invasive plants every year, a significant statistics for a semi-arid country. In addition, eucalyptus trees have notably higher biomass than native vegetation, which can result in increased fires as well as undermine the native biodiversity, especially when invading nature reserves. Overall, alien vegetation has reduced river flow in South Africa by 6.7% and plantations growing in water catchments that supply Cape Town with water have been discovered to use up to two months of Cape Town's water supply every year. As Le Maitre et al, 2002 summarises: "the negative impacts of afforestation include significant reductions in surface streamflow. Commercial plantations are estimated to have reduces surface runoff by 1.4 billion m3 per year" an important reduction considering that less than 10% of South African precipitation becomes surface runoff. 

    The main suggestion offered in order to mitigate the negative impacts eucalyptus plantations on water resources in South Africa is to focus clearing the plantations in and around riparian areas as they use exponentially more water, the more there is available. In addition, while it is important to promote reforestation for a range of benefits, it is more valuable to choose the trees that correspond to the physical characteristics of the land to avoid detrimental impacts such as South Africa is observing. 

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