Felling burnt trees, re-seeding may control water levels in wildfire-hit areas

In areas damaged by wildfire, cutting down the burnt trees and re-seeding the site may help reduce flooding, and return water levels to normal faster, according to a study which may lead to better restoration strategies for areas affected by forest fires.
According to the study, published in the journal Hydrological Processes, water levels are still increased up to 40 years after a forest fire.
“Trees work like straws, pulling water up out of the ground. When you remove them, the water has to go somewhere. Flooding is common after a wildfire, as is elevated stream flow in subsequent summers,” said study co-author Ryan Niemeyer from Washington State University in the US.
“But seeing that the effect lasts for up to 40 years is a little surprising and certainly a new finding,” Niemeyer said.
As part of the study, the scientists looked at the US Forest Service’s Entiat Experimental Forest in north-central Washington, which burned in 1970, likely due to a fire started from a lightning strike.
They assessed three areas of the forest, with the burnt trees in two of them cut down and removed. According to the researchers, these two areas were fertilised and native seeds dropped on the area, while the third area was left untouched.
Based on studies conducted in the early 1970s, the scientists said the water levels in the region’s watershed increased significantly after the fire.
However, the measurement equipment in that study was removed after a few years, they said.
In the current research, the scientists used a new stream flow monitoring equipment and observed the water levels after roughly 40 years. They found that only one of the three areas still had water levels above the pre-fire baseline — the section that was left alone to recover.
“If you visit today, you can easily see that area has less mature vegetation compared to the re-seeded sections. The trees in the re-seeded sections are much bigger, and water levels are back to normal,” Niemeyer said.
According to the researchers, increased water levels can be both positive and negative. If there is more water coming down a stream offering increased access for irrigation, then salvaging any of the burnt logs, or re-seeding the area may not be required, the scientists said.
However, they added that the extra water may impact the land. Since trees help hold soil in place during rains, erosion is higher in areas that aren’t re-seeded, the study noted.
Under this scenario, the sediment going into the watershed from the rains increases, impacting fish and other wildlife.
“It’s really a complex set of interactions, and each wildfire situation effects water and water usage differently. But now we know how long a fire impacts nearby water, and that those impacts can be reduced faster,” Niemeyer said. (PTI)