Wildfire and Erosion
JB: This is Earth and Sky on wildfire and erosion. Normally on a rainy day a canopy of trees covers a forest and softens the impact of driving rain.
DB: But a forest fire can change things and – all too often – flood follows fire. That’s because rain runs off quickly when it falls on soil that’s been burned clear of trees and undergrowth. Later, flood waters erode watersheds and wash sediment into streams and rivers.
JB: Researchers at the Rocky Mountain Research Station in Moscow, Idaho, recently completed a survey of the scientific literature on various strategies for controlling soil erosion after a forest fire. A standard way to control erosion is to seed burned soil with grass. But non-native grasses can displace native plants. And grass needs a full year to take root. So these researchers recommend seeding with barley or winter wheat – grains that grow quickly – and only live for a year. In that year, these grains help hold the soil – afterwards they make room for native plants.
DB: On hilltops, where seeding isn’t very effective, workers take trees felled by fire and align them sideways across hill slopes to slow down flowing water. We have more about wildfire rehabilitation – come to today’s show at earthsky.com. Special thanks today to the National Fish and Wildlife Foundation. We’re Block and Byrd for Earth and Sky.
The following individual was interviewed for today’s show. Our thanks to:
Dr. Peter Robichaud
Research Engineer
USDA Forest Service
Rocky Mountain Research Station
Moscow, Idaho
The following web sites provided information relevant to this script:
“Evaluating the effectiveness of post-fire of post-fire rehabilitation treatments,” “:http://www.fs.fed.us/rm/pubs/rmrs_gtr63.pdfby Peter Robichaud, Jan L. Beyers, and Daniel Neary. USDA Forest Service, Rocky Mountain Research Station, General Technical Report RMRS-GTR-63, September 2000.
National Research Program (US Geological Survey)
More info:
“I look forward to big rainstorms,” said USDA Forest Service research engineer Pete Robichaud. “They help me to understand how soil erosion works.”
Robichaud and his colleagues at the Rocky Mountain Research Station in Moscow, Idaho, recently completed an exhaustive survey of the scientific literature on various strategies for controlling soil erosion after a forest fire. Robichaud noted that the Forest Service alone spent $48 million on post-fire soil-erosion in 1999. That’s up from an average yearly budget of $2 million in the 1970s.
Robichaud was quick to point out that the increased spending doesn’t mean we’re seeing more fires, or that post-fire erosion is getting worse. Instead, said Robichaud, “More people now live at the urban- wild interface.’‘
To some extent erosion control is important to protect habitat; just the same, a certain amount of post-fire erosion is natural, and a part of dynamic ecosystems. So the main factor driving increased spending on post-fire erosion control is to prevent problems for people rather than wildlife. Residents want to see property, roads, and drinking water supplies protected.
Most wildfires create a patchwork of burned areas that vary in severity. Severely burned areas suffer increased erosion due to loss of the protective forest floor layer and creation of water-repellent soil conditions that can cause flooding, downstream sedimentation, and threats to human life and property. High severity burns can increase surface runoff by more than 100 percent. Erosion can increase by three orders of magnitude when high-intesity thunderstorms occur. Fortunately, erosion on burned areas typically decline quickly in subsequent years as the burn areas stablize.
Various treatments are used to reduce runoff and erosion. These include check dams, grade stabilizers, and debris basins in stream channels. Plus forest managers use mulching, grass seeding, contour felled logs (burnt logs laid on the contour to trap runoff and sediment), and ‘straw wattles’ – invented in the 1960s. Wattles are long, narrow plastic mesh bags filled with straw. They’re the same size as tree trunks, but much easier to wrestle into position on a steep slope.
