Forests and water: new research challenges old assumptions about forest restoration

Trees consume water through evaporation and transpiration, so many believed that more trees meant less water for rivers, wells, and agriculture. But a major new synthesis of global evidence, published in Forest Ecosystems, revealed that under the right conditions, restoring forests can actually increase water availability, particularly during critical dry seasons.

The research addresses a key knowledge gap by dissecting the hydrological impacts of large-scale forest landscape restoration (FLR). Scientists from King's College London argue that prioritizing dry-season flow recovery, rather than annual water yield, should be a central goal of FLR.

It demonstrates that by restoring forest cover, we can restore the soil’s natural “sponge.” The roots and organic matter of trees break up hard soil, creating pathways for water to infiltrate. This process can enhance groundwater reserves so significantly that it offsets the water used by the trees themselves, leading to a net gain in the steady, clean baseflow that feeds rivers during dry periods.

“The dominating view that forestation can only reduce streamflow diminishes opportunities to restore the hydrological functioning of degraded landscapes,” said corresponding author Dr. L. Adrian Bruijnzeel. “But a growing body of evidence indicates that the opportunities for forest restoration to improve dry-season flows can indeed be substantial and important in specific geographical settings.”

The study makes clear that the hydrological outcome of restoration is not guaranteed; it depends heavily on local conditions. The benefits are most pronounced in areas with seasonal rainfall, deep soils, and degraded land.

The choice of vegetation is also critical. Fast-growing exotic tree plantations in already dry areas can indeed worsen water scarcity. In contrast, using native species, mixed-age forests, and agroforestry systems with intermediate tree density could be a good choice.

The benefits of forest restoration may extend far beyond the immediate catchment. The article highlights the role of forests in the larger water cycle. Through moisture recycling, evaporation from forest canopies can travel downwind and fall as rain, benefiting agricultural and water systems. In specific coastal and mountainous regions, forests are also adept at capturing water directly from fog and low clouds.

Despite these advances, significant questions remain. The authors call for robust, long-term monitoring of restoration projects to better understand the trade-offs between water use and water infiltration. They advocate for transdisciplinary research that combines soil science, hydrology, and climate modeling to predict outcomes in a changing world.

Forests are not merely water consumers. When restored strategically on degraded lands, they can be powerful engines for water security, biodiversity, and climate resilience. The goal is no longer just to plant trees, but to plant the right trees in the right places for water.