Snowbound: Big trees boost water in forests by protecting snowpack


Date:
March 15, 2022
Source:
S.J. & Jessie E. Quinney College of Natural Resources, Utah State
University
Summary:
Trees have a complex relationship with snow and energy as the
season warms up, but new research shows that big trees can protect
melting snowpacks in water-stressed environments.



FULL STORY ==========================================================================
Big trees play an outsized role in old-growth forests -- from offering
fire resistance to producing strong genetic offspring, big trees give
forests multiple ecological advantages. New research gives managers
yet another reason to honor the behemoths -- big trees protect melting snowpacks in water-stressed environments. The research from Michaela
Teich, Kendall Becker and Jim Lutz from the Department of Wildland
Resources at Utah State University and colleague Mark Raleigh from Oregon
State University, details the ecological puzzle for how big trees interact
with forest snow.


==========================================================================
A good supply of water allows trees to endure hot summer temperatures,
survive wildfire and fight off attacks from invasions of bark beetles. But during the hot summers in the West, precipitation tends to be scant. A
good, thick snowpack is water-in-the-bank as far as forests are concerned;
the longer the winter snowpack endures into spring and summer months,
the longer water is released into the soil and available to thirsty
trees. That melting snow is also part of the runoff that fills the West's reservoirs and benefits communities. The goal of the research was to
find ways for managers to help this essential source of water linger
for longer into spring and summer months.

A hindrance for building a snowpack in a forest is, ironically, the trees themselves. Tree branches catch snow before it hits the ground and offers
it back up to the atmosphere through evaporation or sublimation. The
ground directly beneath big trees, cut off from the sky by branches,
tends to build only a shallow snowpack, while forest floors further away
enjoy deeper accumulations. Add to that equation longwave radiation --
any tree with a good, solid heft to its trunks emits an invisible energy
that humans can't see (as light) or feel (as heat). But the constant
subtle bombardment inflicted on the adjacent snowpack adds just enough
energy to pull snow back from the threshold of frozen, and to limit how
long it can endure into the warm season.

But big trees aren't all bad news for snowpacks. The same, wide branches
that prevent snow from reaching the ground directly under a tree also
provide a cooling stretch of shade that blocks direct sunlight from
melting snow across a fairly wide radius surrounding a tree. And the
savings are significant; they can outweigh both the detriment of canopy
cover and longwave energy.

With the balance between these factors in mind, the researchers performed calculations to determine what a forest looked like that maximized the
benefits of shade, and minimized the negative factors of canopy and
longwave energy.

What they found was a doughnut .... at least a doughnut-shaped zone
surrounding big trees where snowpack could best endure, away from the
longwave energy produced by the trunk and still within the reach of
the cooling shade. The best forests for long-lasting snowpack had trees
that were spaced in such a way that these doughnut-shaped zones bumped
up against each other, but did not overlap.

"Snow is a key resource for fresh water supply and ecosystem function. Our study highlights that conserving big trees -- the very trees that often
survive forest fires -- in forest ecosystems where fire is part of the ecological cycle can help facilitate both," said Teich.

But spaced-out trees need to be both healthy and big for the equation
to work, say the researchers. Healthy, because thick tree canopies cast
the most shade.

And big, because those trees are tall and cast shade further -- plus
being more likely to resist wildfires occurring in the West.

"This work, in a large Smithsonian-affiliated research site, lays
out the fundamental issues involved in retaining snow on the ground"
says Lutz. "What we need now is more investigation into the specific
tree species, sizes, and densities that optimize snow retention in the different forest types of the American West."

========================================================================== Story Source: Materials provided by S.J._&_Jessie_E._Quinney_College_of_Natural_Resources,
Utah_State_University. Original written by Lael Gilbert. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Michaela Teich, Kendall M. L. Becker, Mark S. Raleigh, James
A. Lutz.

Large‐diameter trees affect snow duration in post‐fire
old‐growth forests. Ecohydrology, 2022; DOI: 10.1002/eco.2414 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/03/220315141844.htm

--- up 2 weeks, 1 day, 10 hours, 51 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1:317/3)