According to the Forestry Research Programme of The United Kingdom, planting trees can decrease the amount of available surface water and enable desertification instead of reducing it, reports Fred Pearce of New Scientist. The report says that in some places planting more trees follows the conventional wisdom that trees help prevent floods and store water.
However, in other places the planted trees can actually lower water tables and make areas increasingly dry. The growth of alien pine and eucalyptus trees in South Africa was cited in the report, where the trees are thought to cut river flow by three percent.
A study revealed that the continuous spread of these invasive pine trees will dwindle the Cape's water supply and hinder the natural diversity of the fynbos region. Not only do these alien plants enable desertification, but sustaining them will also have a negative impact in monetary terms.
"If the current rate of pine invasion continues over the next 100 years, Cape Town will lose 30% of its water supply through a loss of runoff to its storage dams," Dr Brian van Wilgen, Chief Ecologist at the Council For Scientific and Industrial Research at Stellenbosch University, predicts.
The gradual decline of ecosystem services such as water was estimated at R2 billion annually. "There is no way that this loss can be offset by on-going forestry endeavours under a scenario of 'business as usual'," says Dr van Wilgen.
Legal efforts that command landowners and growers to take effective steps against invasive species have remained unenforced.
According to Dr van Wilgen, higher levels of funding and control operations through schemes that use payments for ecosystem services could progress towards an environment free of invasive species. Raising awareness on reasons to completely remove certain tree species from specific ecosystems, and to continue efforts to find suitable biological control agents to effectively help manage the spread of invasive species are all steps that could contribute to an invasive species free ecological system.