Bigleaf maple decline tied to hotter, drier summers in Washington state,
U.S.

Date:
September 30, 2021
Source:
University of Washington
Summary:
A new study has found that recent bigleaf maple die-off in
Washington is linked to hotter, drier summers that predispose this
species to decline.

These conditions essentially weaken the tree's immune system,
making it easier to succumb to other stressors and diseases.



FULL STORY ==========================================================================
As its name suggests, the bigleaf maple tree's massive leaves are perhaps
its most distinctive quality. A native to the Pacific Northwest's wet
westside forests, these towering trees can grow leaves up to 1.5 feet
across -- the largest of any maple.


==========================================================================
But since 2011, scientists, concerned hikers and residents have
observed more stressed and dying bigleaf maple across urban and suburban neighborhoods as well as in forested areas. Often the leaves are the first
to shrivel and die, eventually leaving some trees completely bare. While
forest pathologists have ruled out several specific diseases, the overall
cause of the tree's decline has stumped experts for years.

A new study led by the University of Washington, in collaboration with Washington Department of Natural Resources, has found that bigleaf
maple die- off in Washington is linked to hotter, drier summers that
predispose this species to decline. These conditions essentially weaken
the tree's immune system, making it easier to succumb to other stressors
and diseases. The findings were published Sept. 16 in the journal Forest Ecology and Management.

"These trees can tolerate a lot, but once you start throwing in other
factors, particularly severe summer drought as in recent years, it
stresses the trees and can lead to their death," said co-author Patrick
Tobin, associate professor in the UW School of Environmental and Forest Sciences.

In addition to warmer, drier weather, the researchers found that bigleaf
maple are more likely to decline near roads and other development --
especially in hotter urban areas. Across multiple years and sites in
Western Washington, they weren't able to find any single pest or pathogen responsible for the mass decline; rather, all signs point to climate
change and human development as the drivers behind the regional die-off.

"Managing, protecting and utilizing our urban and wild ecosystems in the
face of climate change and human population growth is and will continue to
be one of the major challenges facing us," said lead author Jacob Betzen,
a biological technician with the U.S. Forest Service who completed this
work as a UW graduate student. "This research investigating bigleaf maple
is one small piece of that larger puzzle." From field sampling and lab
work, the researchers found that bigleaf maple grew less in summers that
were hot and dry, both in their overall mass as well as leaf size. One of
the signature signs of distress, they found, was significantly smaller
leaves. In drought conditions, trees use more energy trying to survive
and defend themselves from diseases and other threats.



========================================================================== "These results show that summer heat and drought impact the health of
iconic tree species of Washington, like bigleaf maple, even in Western Washington, a region known for abundant precipitation. Health impacts to
our forests and tree species are likely to continue as we have increased periods of drought each year," said co-author Amy Ramsey, an environmental planner and forest pathologist with Washington DNR.

For this study, the research team revisited a selection of sites around
Western Washington where DNR in 2014 and 2015 had taken samples and
performed testing on trees in decline. They also chose 36 roadside sites
where maples were present. Finally, they randomly selected an additional
59 sites on public land across the region where bigleaf maple are known
to exist. Across these randomly chosen sites, they found that nearly a
quarter of the bigleaf maple trees showed signs of decline.

From each study site, they collected soil, leaves, stems and tree cores,
which they analyzed in the lab. Tree cores allow scientists to learn
about the age and growth rate of a tree -- as well as weather history
at that location - - without having to cut it down.

From the analysis of the tree cores, the team found that the growth of
bigleaf maple has varied significantly since 2011, and was especially
lower in years with hotter, drier summers. They compared this growth to
that of Douglas fir trees, which they also cored, and found their annual
growth was consistent - - meaning that bigleaf maple are especially
sensitive to dry, hot weather.

"For us, these analyses were a big piece of the puzzle," Tobin said. "This helped us determine that their decline is a recent phenomenon that is
linked to weather conditions." These findings will likely change the
way foresters manage bigleaf maple in both urban and wild settings. This
might mean planting the trees in different locations, watering more in
urban areas or using seed stock better adapted to the projected future conditions of a site, Betzen said. In forests, it might mean a focus on
keeping intact landscapes free from more urbanization.

Other co-authors are Gregory Ettl of the UW and Daniel Omdal of
Washington DNR.

This research was funded by the U.S. Department of Agriculture NIFA
McIntire- Stennis Cooperative Forestry Program, Washington DNR and the
David R.M. Scott Endowed Professorship in Forest Resources.

========================================================================== Story Source: Materials provided by University_of_Washington. Original
written by Michelle Ma. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Jacob J. Betzen, Amy Ramsey, Daniel Omdal, Gregory J. Ettl,
Patrick C.

Tobin. Bigleaf maple, Acer macrophyllum Pursh, decline in western
Washington, USA. Forest Ecology and Management, 2021; 501: 119681
DOI: 10.1016/j.foreco.2021.119681 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210930111107.htm

--- up 4 weeks, 8 hours, 25 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)