Driven by climate, more frequent, severe wildfires in Cascade Range
reshape forests

Date:
September 24, 2020
Source:
Portland State University
Summary:
New research found that while the increased wildfire activity is
causing widespread changes in the structure and composition of
these mid-to-high elevation forests, the new landscapes are also
likely more resilient to projected upward trends in future fire
activity and climate conditions.



FULL STORY ==========================================================================
In recent years -- and 2020 is no exception -- parts of the Pacific
Northwest that are typically too wet to burn are experiencing more
frequent, severe and larger wildfires due to changes in climate. New
research from Portland State University found that while the increased
wildfire activity is causing widespread changes in the structure and composition of these mid-to-high elevation forests, the new landscapes
are also likely more resilient to projected upward trends in future fire activity and climate conditions.


==========================================================================
The study, led by PSU graduate student Sebastian Busby, examined temperate forests that burned expansively, severely and repeatedly between 2003 and
2015 in the central Cascade Range of Oregon and Washington. On Mt. Adams,
these wildfires included the 2008 Cold Springs, 2012 Cascade Creek and
2015 Cougar Creek fires. On Mt. Jefferson, the wildfires included the 2003 Booth and Bear Butte Complex, 2007 Warm Springs Area Lightning Complex
and 2014 Bear Butte 2 fires. Some areas Busby studied have burned again
this summer as part of the Lionshead fire in the Mt. Jefferson area.

Busby said that historically, wet and cool climate limited fire events
in these humid forest environments to an interval of 50 to 200-plus
years. But climate change has led to warmer winters, reduced mountain
snowpack and longer, drier summers and fire seasons. The time between
repeated wildfire events in this study was less than 12 years.

"These forests are drying out earlier in the year, making them more
vulnerable to frequent, severe and larger wildfires," Busby said. "Because these forests have not historically burned very often, they're composed
of high densities of tree species that are not well-adapted to frequent
and very large severe fires." True firs were the dominant conifer tree
species across the study areas, but post-fire tree regeneration was
generally very poor due to a lack of live mature trees remaining after
the fires to reseed the forest.

The burned areas, however, did support the establishment of pines at a
low density, which are functionally better adapted to fire. The findings suggest that in the near term, these forests may transition from a dense fir-dominated conifer forest into a patchy, low-density, pine-dominated
forest that will likely lack the fuel connectivity conducive to crown
fires. Busby said that while widespread forest composition change and
forest cover loss may be alarming, the results indicate that the altered structure and composition are likely to be more resilient in the face of
future fire and climate conditions, such as drought and heatwave events.

"From an ecological point of view, these reburned forests are going
to have a greater abundance of tree species that are better adapted to
fire and potentially have less flammable forest structure overall," he
said. "Now, in these post-reburned forests that are growing in a warmer
and drier world, it will be up to us to decide whether we let future
fires burn or not." If forest managers and other stakeholders choose
to suppress them, they risk returning these forests to their historical
dense structures, which thrived in cool and wet climates. However,
under ongoing warming conditions, this alternative might increase the likelihood of severe and expansive fires in the future, negatively
impacting human life, property, and natural resources.

"Wildfires are a natural ecological process on these landscapes and
have been for thousands of years," Busby said. "Wildfire can be a
great catalyst for change, but that change doesn't have to be entirely negative. We must learn to co-exist with wildfires, use them effectively,
and embrace the positive elements they bring to our regional forests and ecosystems." The findings are published in the journal Ecosphere. Busby's co-authors are Andre's Holz, associate professor of geography at PSU,
and Kevan Moffett, assistant professor of environmental hydrology at
Washington State University- Vancouver.


========================================================================== Story Source: Materials provided by Portland_State_University. Original
written by Cristina Rojas. Note: Content may be edited for style and
length.


========================================================================== Journal Reference:
1. Sebastian U. Busby, Kevan B. Moffett, Andre's
Holz. High‐severity
and short‐interval wildfires limit forest recovery
in the Central Cascade Range. Ecosphere, 2020; 11 (9) DOI:
10.1002/ecs2.3247 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200924141605.htm

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