Study shows removal of trees makes wetlands wetter

Study shows removal of trees makes wetlands wetter
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. Credit: Craig Woodward

(Phys.org) —A small team of Australian researchers has found that cutting down trees in a wetland area, tends to make the area even wetter. In their paper published in the journal Science, the team describes a study they undertook analyzing wetlands in Australia and historical records from other sites around the world to come to their conclusions.

The modern mantra has always been that cutting down large numbers of trees is always bad for the environment—doing so means less carbon dioxide is taken out of the atmosphere, contributing to global warming, etc., and planting new ones to replace those that were lost is always a good thing. In this new study, the team in Australia argues that cutting down trees, such as was done in the Northern Tablelands in the New England region of New South Wales Australia, in the mid 1800's, led to what is now Little Llangothlin Lagoon, a protected water body that hosts a wide variety of plant and animals that are now dependant on the wetland ecosystem. Research there by the team uncovered artifacts that suggest that before people arrived on the scene, there wasn't a lake at all, in fact, it was more like what the team calls a swamp that was wet only during certain periods of .

Wetlands grow wetter when trees are removed, the team claims, because trees pull water out of the ground via their roots, a large amount of which winds up in the atmosphere after being emitted from the leaves. After analyzing data generated by other researchers over time of 317 other wetland areas across the globe, the team has calculated that approximately 10 percent of them have been made wetter by deforestation.

The researchers suggest their findings should be taken into account by land managers—trying to replace trees in wetlands, could they say, reduce water amounts and disrupt sensitive systems that have evolved to take advantage of the changed landscape. Planting , they add, could wind up in a loss of rare plant or animal species. They add that their analyses revealed that tree cutting in the areas studied resulted in what would have happened had there been a 15 percent increase in rainfall. They suggest that further studies be done and that changes in water amounts be taken into consideration by land managers when making decisions.

Study shows removal of trees makes wetlands wetter
A short core sample from Little Llangothlin Lagoon, Australia. Gravity cores like this one preserve a detailed history of changes in the wetland hydrology through time. The plants on the top are charophytes, which did not become common in this wetland until after 1840, when clearance of the forest nearby changed the wetland into a semi-permanent lake. Credit: Craig Woodward

Explore further

Researchers find trees worldwide more sensitive to drought than previously thought

More information: The hydrological legacy of deforestation on global wetlands, Science 14 November 2014: Vol. 346 no. 6211 pp. 844-847 DOI: 10.1126/science.1260510

Abstract
Increased catchment erosion and nutrient loading are commonly recognized impacts of deforestation on global wetlands. In contrast, an increase in water availability in deforested catchments is well known in modern studies but is rarely considered when evaluating past human impacts. We used a Budyko water balance approach, a meta-analysis of global wetland response to deforestation, and paleoecological studies from Australasia to explore this issue. After complete deforestation, we demonstrated that water available to wetlands increases by up to 15% of annual precipitation. This can convert ephemeral swamps to permanent lakes or even create new wetlands. This effect is globally significant, with 9 to 12% of wetlands affected, including 20 to 40% of Ramsar wetlands, but is widely unrecognized because human impact studies rarely test for it.

Journal information: Science

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Citation: Study shows removal of trees makes wetlands wetter (2014, November 14) retrieved 15 October 2019 from https://phys.org/news/2014-11-trees-wetlands-wetter.html
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Nov 14, 2014
This has long been know by ALL land owners.
Remove the mesquite and elms and the water returns.
We have known this for fifty years and more.

Nov 15, 2014
True, this has also been known in Western Australia for a long time, in that adding trees lowers the water table, ostensibly so any rising water from lower depths reduces therefore rless propensity to carry up deep salt which, with our hot summers, dries quickly leaving areas of salt lake due to land clearing in some south western regions. Some farmers have taken to trying another approach with hydrostatic pressure, by not planting trees but artificially flooding areas to provide pressure to force water down where possible strata permitting. Ostensibly so that some years later the land can be drained when salt levels have reduced but, until then often extra water has to come from somewhere !

One of our weirs is now too salty to use for drinking water. That & climate change means we have lower rainfall overall & had it not been for a sizable desalination plant we would be in trouble with even stricter water restrictions than we still have in summer !

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