Deforestation makes wetlands wetter

Removing trees from the world’s wetlands, such as swamps, bogs and marshes, makes these environments significantly wetter and may even create new wetlands.

Little Llangothlin Lagoon, Australia. Clearance of the forest around this wetland after 1840 by European settlers changed it from an ephemeral wetland to a semi-permanent lake. This wetland is a Ramsar-listed wetland. Photo credit: Craig Woodward.

This phenomenon goes largely unrecognised, according to researchers from the University of Queensland and the Australian Nuclear Science Organisation, because most studies of human impacts on the environment are not designed to look for it.

Traditionally, studies have focused on the quality rather than quantity of water in the world’s wetlands after they’ve been deforested - with the most commonly reported impact being higher levels of nutrients.

But Craig Woodward and colleagues have show that the main effect of deforestation on wetland environments is an increase in water. In some cases this extra water is equivalent to 15% more annual rainfall.

The researchers used a detailed model of water exchange between Earth and the atmosphere and analysed data from more than 250 reports on 317 global wetlands sites where deforestation and changes in wetlands have been recorded. They also looked at fossil records from Australia and New Zealand to show that deforestation has been creating new wetlands and increasing the water levels of existing wetlands for thousands of years.

The results suggest the effect is globally significant with 9 to 12% of wetlands affected.

The findings also suggest that conservation efforts to preserve the world’s wetlands need to be revised to take this effect into account and that the reforestation of wetlands - a strategy that is currently planned in many regions of the world - may have unintended consequences, altering water balances such that wetlands disappear.

This study has been published in Science