Snow cover critical for revegetation following forest fires
Study finds climate change a factor in decrease of snowpack in the
Western United States

Date:
November 22, 2021
Source:
University of Nevada, Reno
Summary:
With wildfires devastating mountain ecosystems across the western
United States, their successful forest revegetation recovery
hinges on, among other factors, an adequate lasting snowpack,
according to new research.



FULL STORY ==========================================================================
With wildfires devastating mountain ecosystems across the western United States, their successful forest revegetation recovery hinges on, among
other factors, an adequate lasting snowpack, according to research by
the University of Nevada, Reno and Oregon State University.


==========================================================================
"Our study illustrated that summer precipitation, snow cover and elevation
were all important drivers of revegetation success," said Anne Nolin,
a hydrologist and geography professor at the University of Nevada,
Reno and formerly at Oregon State University. "In particular, we found
that snow cover was a critical explanatory variable for revegetation in
the Oregon and Washington Cascades. This could help inform revegetation management practices following severe wildfires." Climate change has
already increased the fraction of winter precipitation that falls as rain rather than snow, reduced the spring snow water equivalent -- a metric for
how much water snow contains -- and caused snowmelt to begin earlier in
the spring than it used to, Nolin explained. Pacific Northwest snowpacks
have seen the greatest declines of any seasonal snow region in the West.

The research, led by Nolin, examined the 260,000-square-mile Columbia
River Basin in the Pacific Northwest. She teamed with co-author Andrew
Wilson, a graduate research assistant in OSU's College of Earth, Ocean,
and Atmospheric Science, and co-author Kevin Bladon of OSU's College of Forestry for the study.

The NASA-supported study featured before-and-after vegetation analyses
for two dozen high-severity wildfires. The fires occurred over a
10-year period among the four distinct subregions of the Columbia River
Basin. There are many short- and long-term effects from these fires,
including erosion, debris flows and water quality issues, which can
affect the health of aquatic ecosystems and downstream community water
supply, highlighting the importance of understanding post-fire forest rehabilitation.

In their paper published in the Journal of Geophysical Research - - Biogeosciences, "Assessing the Role of Snow Cover for Post-Wildfire Revegetation Across the Pacific Northwest," the findings show that
given the trends of increasing wildfire activity, lower snowpacks,
and earlier snow disappearance dates across the Pacific Northwest,
forests will likely experience more frequent drought conditions, which
will negatively impact the success of post?wildfire vegetation recovery
with a number of impacts to the ecosystem.



========================================================================== "This knowledge may be used to facilitate adaptive post-fire management policies and decisions to ensure long-term forest health," Nolin, who is
also director of the University of Nevada, Reno's Graduate Program of Hydrological Sciences, said. "For example, depending on the sub-region
and species composition, reseeding efforts following low snow winters
might employ more drought tolerant species or, replanting could be
delayed one to two years until snowmelt and soil moisture conditions
are more favorable for seedling propagation.

"However, climate change projections and shifting wildfire regimes
have increased concerns about post-fire regeneration and, as such it is imperative that we broaden our understanding of the role of snowpacks
in post-wildfire forest regeneration. The snowpacks' role in aiding revegetation will become increasingly important across the West. And
where snowpacks have declined, there likely will be ecosystem transitions
that look like a shift from forest to non-forest and from evergreen to deciduous vegetation." Wildfires continue to burn more area each year
across many regions of the planet, including the Pacific Northwest. The
Pacific Northwest's largest watershed, the Columbia River Basin contains
a variety of fire-prone landscapes that have seen almost 900 fires since
2010, serves as critical habitat for more than 700 species and is a
water source for seven states.

"As wildfire activity continues to increase and intensify in the
Northwest, understanding what shapes revegetation on severely burned
forested landscapes is vital for guiding management decisions," co-author Bladon said.

After the occurrence of a wildfire, revegetation over the burned area is critical to maintain or re-establish ecosystem functions from forests
such as biodiversity, erosion control, water purification and habitat provision.



========================================================================== "Snow matters to regrowing vegetation following fire, and with double
impacts of declining snowpacks and increasing wildfires it is critical
that we understand how these changes are affecting Pacific Northwest
forests," Nolin said. "Positive relationships between snow cover and
summer precipitation with post-fire greening suggest that active post-fire revegetation efforts will help facilitate recovery, especially during
years when severe wildfires are followed by early snowmelt years or
below average summer precipitation." In the study, summer precipitation consistently appeared as the most important variable driving post-fire revegetation across all four subregions. Snow cover frequency, along
with elevation, were shown to be secondary but significantly influential explanatory variables for revegetation in the Oregon and Washington
Cascades.

More than 80% of wildfires in the western United States from 2000 to
2012 burned within a seasonal snow zone, a time period that overlaps
with the years studied by the scientists.

"As wildfire activity continues to increase and intensify in the
Northwest, understanding what shapes revegetation on severely burned
forested landscapes is vital for guiding management decisions,"
Bladon said. "But variables such as snow cover frequency, pre-fire
forest composition, and elevation, were also shown to be significantly influential for revegetation in the Oregon and Washington Cascades."
Wildfire season length in the western U.S. overall has increased by
roughly 25 days in recent decades, including a massive increase in the Northwest from the mid-1970s, when it was 23 days, to 116 days in the
early 2000s. That's attributable mainly to warmer temperatures and drier conditions in the spring and summer.

"Snow cover has a strong influence on postfire vegetation greening, but
the influence varied depending on subregion and dominant prefire conifer species, with the biggest impacts at low to moderate elevations in the Washington Cascades, the Oregon Cascades and western Montana Rockies,"
Nolin said. "And with current climate change projections, snowpacks'
role in aiding revegetation will become increasingly important across
the West." Bladon suggests fire can be looked at as an opportunity for
forests to reassemble into ecosystems better suited to survive warmer
winters, longer fire seasons and more drought stress.

"That's at the heart of the challenge of reconciling a changing climate's ecological forces with postfire forest management goals -- the goals
are often oriented toward re-establishing forests as they existed before
the fire," Bladon said. "But with shifting climate trends in the region,
that might not be the most adaptive path forward for forested landscapes." ========================================================================== Story Source: Materials provided by University_of_Nevada,_Reno. Original written by Mike Wolterbeek. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Andrew C. Wilson, Anne W. Nolin, Kevin D. Bladon. Assessing the
Role of
Snow Cover for Post‐Wildfire Revegetation Across the Pacific
Northwest. Journal of Geophysical Research: Biogeosciences, 2021;
126 (11) DOI: 10.1029/2021JG006465 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/11/211122172630.htm

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