Forests ‘less resilient’ after wildfires

WITH wild fires raging in California, American researchers say their studies show that with a warming climate, forests are less resilient after wildfires.

As a result, the Colorado State University study finds the forests we see today are not what we will see in the future.

“We often talk about climate change and how it will affect us in the future, but the truth is we are already seeing those changes,” says Camille Stevens-Rumann, an assistant professor in the Department of Forest and Rangeland.

“Disturbances like wildfires are a catalyst for change. In many places, forests are not coming back after fires.”

The researchers analysed data from nearly 1,500 sites in five states – Colorado, Wyoming, Washington, Idaho, and Montana – and measured more than 63,000 seedlings after 52 wildfires that burned over the past three decades.

They wanted to understand if and how changing climate over the past several decades affected post-fire tree regeneration, a key indicator of forest resilience.

They found sobering results, including significant decreases in tree regeneration following wildfires in the early 21st century, a period markedly hotter and drier than the late 20th century.

“What we’ve found is dramatic, even in the relatively short 23-year study period,” Stevens-Rumann says.

Historically, forests change over time. But the research team said its findings suggest that it will take much longer after a wildfire for sites to return to forests, if they return at all.

In a third of the areas studied, researchers found no seedlings growing. The hardest-hit sites were the warmest and driest, and those where fires burned so severely that few trees survived to provide seed.

“Even if we plant trees in those areas, it’s unlikely to be successful,” Stevens-Rumann says.

“We need to start expecting that these landscapes aren’t going to look the same in the future, whether it’s reduced density of trees or no longer a forest.”

One of the big surprises for the team was seeing the data for the average annual water deficit at study sites.

“In my lifetime, you can see these sites becoming substantially hotter and drier,” she said. “Many forest managers want post-fire years to be cooler and wetter, to help with regeneration, and that’s just not happening anymore, or happening very infrequently.”

Meanwhile in Canada, University of British Columbia researchers says forested areas are critically important water resources, but as land is developed or the green vegetation is destroyed, watersheds are irreversibly damaged.

The changes to ground vegetation can have as much of an impact on global water resources as climate change.

Earth, Environmental and Geo-graphic Sciences Professor Adam Wei says entire watersheds are being affected.

PhD candidate Qiang Li says forest cover is an important element.

“Scientists talk about how climate change affects water when they measure global warming,” Li says.

“We’re suggesting they also need to keep an eye on forest vegetation. It’s a key indicator of the health of our water resources.”

Wei says simulations show the average global alteration in annual water flow due to vegetation change is as high as 31 per cent.

“Our results also show that on average, in 51 per cent of the study area, vegetation change and climate change operate together and can lead to either fewer water resources, meaning higher chances of drought, or an increase in water supply

and higher chances of devastating floods.


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