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U.K. study touts flooding protection benefits of tree planting

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woodland and stream
The University of Plymouth study states that within just 15 years of establishing more woodlands, soil saturated hydraulic conductivity can double, increase the “wetness threshold”, and reduce surface soil compaction and bulk density. Credit: HIROSHI UEDA, AdobeStock.

New research from the U.K. suggests that trees, forests and woodlands are a staple of green infrastructure that can enhance soil’s ability to absorb rainwater while providing a host of other benefits to build resilience as flood events increase.

The University of Plymouth found that proper placement of the trees is key in terms of maximizing gains for stormwater management and flood protection. According to the study, published in the journal Land Degradation & Development, higher elevation areas, or uplands where soils are more resilient, may be prime spots for planting en masse, which is considered a form of natural flood protection.

“[…] Consultation and cooperation with farmers and land managers with local soil knowledge will be essential if the environmental benefits associated with woodland are to be maximized, and to more widely ensure the sensitive implementation of nature‐based solutions to climate change,” the study’s authors state.

The study describes how trees mitigate flooding primarily through three factors: higher water use that increases water absorption capacity within soils and reduces surface water runoff; greater hydraulic “roughness and canopy interception” that increases water loss through evaporation and reduces velocity of surface runoff through temporary floodwater retention; and lastly, trees improve soil structure by enhancing water infiltration, increasing water storage and reducing runoff.

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Within just 15 years of establishing more woodlands, soil saturated hydraulic conductivity can double, increase the “wetness threshold” and reduce surface soil compaction and bulk density, the researchers say.

The study’s authors state that a “legacy of soil compaction from long-term over‐grazing” combined with high but declining livestock numbers, has left many upland soils in the U.K. in poor condition.

“Heavily grazed, compacted areas can become active source areas for runoff generation by lowering the threshold between dry and wet soil states,” the study states.

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