Quantcast
Environmental News for a Healthier Planet and Life

New Forests Planted Near Rivers Could Use up All the Water, Study Finds

Science
New Forests Planted Near Rivers Could Use up All the Water, Study Finds
New pine trees grow from the forest floor along the North Fork of the Flathead River on the western boundary of Glacier National Park on Sept. 16, 2019 near West Glacier, Montana. Chip Somodevilla / Getty Images

By Alex Kirby

New forests are an apparently promising way to tackle global heating: the trees absorb carbon dioxide, the main greenhouse gas from human activities. But there's a snag, because permanently lower river flows can be an unintended consequence.


A study by scientists at the University of Cambridge, UK, has found that river flow is reduced in areas where forests have been planted − and, significantly, it does not recover over time. Rivers in some regions can disappear completely within 10 years.

This, the researchers say, highlights the need to consider the impact on regional water availability, as well as the wider climate benefit of tree-planting plans.

"Reforestation is an important part of tackling climate change, but we need to carefully consider the best places for it. In some places, changes to water availability will completely change the local cost-benefits of tree-planting programmes", said Laura Bentley, a plant scientist in the University of Cambridge Conservation Research Institute, and first author of the report.

Age Effect Missed

Planting large areas of trees has been suggested as one of the best ways of reducing atmospheric carbon dioxide levels, because trees absorb and store the gas as they grow, although uncertainties about the strategy persist. Science has known for a long time that planting trees reduces the amount of water flowing into nearby rivers, but no-one had realized how this effect changes as forests age.

The Cambridge study looked at 43 sites across the world where forests have been established, and used river flow as a measure of water availability in the region. It found that within five years of planting trees, river flow had reduced by an average of 25%.

But 25 years after the trees were planted, rivers had gone down by an average of 40%, or in a few cases had dried up altogether. The biggest percentage reductions in water availability were in parts of Australia and South Africa.

"River flow does not recover after planting trees, even after many years, once disturbances in the catchment and the effects of climate are accounted for," said professor David Coomes, director of the Conservation Research Institute, who led the study.

Published in the journal Global Change Biology, the research showed that the type of land where trees are planted determines the impact they have on local water availability.

Trees planted on natural grassland where the soil is healthy decrease river flow significantly. But on land previously degraded by agriculture, establishing a forest helps to repair the soil so that it can hold more water, and therefore decreases nearby river flow by a smaller amount.

Strangely, the effect of trees on river flow is smaller in drier years than in wetter ones. When trees are drought-stressed they close the pores on their leaves to conserve water, and as a result take up less water from the soil. In wet weather, though, they use more water from the soil, and also catch the rainwater in their leaves.

"Climate change will affect water availability around the world," said Bentley. "By studying how forestation affects water availability, we can work to minimize any local consequences for people and the environment."

Reposted with permission from Climate News Network.

By Frank La Sorte and Kyle Horton

Millions of birds travel between their breeding and wintering grounds during spring and autumn migration, creating one of the greatest spectacles of the natural world. These journeys often span incredible distances. For example, the Blackpoll warbler, which weighs less than half an ounce, may travel up to 1,500 miles between its nesting grounds in Canada and its wintering grounds in the Caribbean and South America.

Read More Show Less

EcoWatch Daily Newsletter

Kevin Maillefer / Unsplash

By Lynne Peeples

Editor's note: This story is part of a nine-month investigation of drinking water contamination across the U.S. The series is supported by funding from the Park Foundation and Water Foundation. Read the launch story, "Thirsting for Solutions," here.

In late September 2020, officials in Wrangell, Alaska, warned residents who were elderly, pregnant or had health problems to avoid drinking the city's tap water — unless they could filter it on their own.

Read More Show Less

Trending

Eat Just's cell-based chicken nugget is now served at Singapore restaurant 1880. Eat Just, Inc.

At a time of impending global food scarcity, cell-based meats and seafood have been heralded as the future of food.

Read More Show Less
New Zealand sea lions are an endangered species and one of the rarest species of sea lions in the world. Art Wolfe / Photodisc / Getty Images

One city in New Zealand knows what its priorities are.

Dunedin, the second largest city on New Zealand's South Island, has closed a popular road to protect a mother sea lion and her pup, The Guardian reported.

Read More Show Less

piyaset / iStock / Getty Images Plus

In an alarming new study, scientists found that climate change is already harming children's diets.

Read More Show Less