CORVALLIS, Ore. — After wildfires burn vegetation surrounding rivers, fish in those rivers appear unaffected by a lack of shade cover to cool the waters to a comfortable temperature, University researchers report Oregon State.
OSU researchers say vegetation in areas immediately surrounding a stream provides shade, cooling the stream to a comfortable temperature for freshwater fish such as rainbow trout, cutthroat, and rainbow trout of Sant Martí
When a wildfire sweeps through the area and burns away all the vegetation, as it did in 2020 in the OSU study area around Douglas County’s Hinkle Creek, researchers hoped that the lack of shade to warm the waters, killing the fish or forcing them to migrate to colder streams. Instead, researchers found in the summer of 2021 that most fish populations actually increased in streams where surrounding vegetation burned.
“These are ecologically, culturally, and economically important species distributed throughout western North America,” said study leader Dana Warren with OSU’s Colleges of Forestry and Agricultural Sciences.
“Recent studies have speculated about the potential effects of climate change on trout and salmon as summer stream temperatures gradually rise between 16 and 20 degrees Celsius. [61 to 68 degrees Fahrenheit]. Abrupt disturbances such as fire can produce rapid and substantial increases in stream temperatures that provide information not only about how these increasingly common disturbance events affect native salmonids, but more broadly how salmonids may respond to other aspects of climate change”.
The OSU scientists are quick to point out that their findings do not necessarily indicate that wildfires have no negative impact on fish populations. The study will take several more years, and the researchers have not been able to study the long-term effects of wildfires on the fish. These may include population declines that do not occur immediately, as well as negative impacts on overall fish health.
“Acute mortality is important, but it’s not the only impact,” Warren said. “There may be sublethal effects, such as a weakened ability to grow or reproduce. Given the short-term nature of our observations, more research is needed into the mechanisms driving fish responses to warmer water temperatures, and long-term follow-up is also needed.”