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March 24, 2021
By Lon TegelsCollege of Forestry, Agriculture and Natural ResourcesThe University of Arkansas at Monticello
(Word Count 1,689)
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Download related PHOTOS: https://flic.kr/s/aHsmUCmn6a
EDS: SUBS 27th graf to correct Missouri to Mississippi
MONTICELLO, Ark. — Doing forest research can be a lonely occupation. Ask the University
of Arkansas at Monticello graduate student Jonathan Kressuk. The sun isn’t even up
yet. It’s the first hard freeze of the season in Southern Arkansas. Kressuk is wading
through a foot of water, hauling bags of ice into the forested wetlands in Cut-Off
Creek Wildlife Management Area near Dermott, Arkansas.
His mission is to chill the stems of the willow oak seedlings growing naturally on
the forest floor. He will measure tree roots’ respiration, akin to breathing in animals,
at various air temperatures.
“Most people think of the leaves of trees taking in carbon dioxide for photosynthesis
and releasing oxygen, but roots use oxygen and sugars produced by leaves to get their
energy-releasing carbon dioxide, just like humans and animals do when they breathe,”
said Ben Babst, UAM associate professor and Arkansas Agricultural Experiment Station
researcher with the Arkansas Forest Resources Center.
Kressuk is working with Babst on a five-year research project. Ultimately, it will
provide forest landowners and forest managers with information about when it is safest
to flood their bottomland hardwood forests within green tree reservoirs without damage
to the trees or their root systems. Ducks love flooded forests. Certain species of
oak trees provide small acorns that ducks thrive on, along with other ecosystem benefits.
The key is to flood the forest, providing an attractive environment for ducks without
killing off the oaks that comprise their food supply.
Kressuk is trying to determine the role air temperatures play in tree dormancy. “Today,
I’m testing the effects of two different air temperatures on root activity on willow
oak seedlings, trying to see if air temperature affects how roots are growing,” said
The experiments are part of a larger project related to human-made flooding of southern
Arkansas’s bottomland hardwoods. Kressuk’ s master’s degree involves measuring tree
roots’ activity when the stems experience different air temperatures.
Roots grow too slowly to measure growth in a single day. But root respiration tends
to track growth, providing a snapshot. This root respiration reveals how much overall
root activity is happening now. Kressuk said he also spent a good deal of his research
measuring root growth directly by pulling up the roots from the ground, drying them
out, and measuring their weight.
Historically, bottomland hardwood forests used to flood naturally and seasonally.
But as European civilization migrated west, much of that natural flooding was eliminated
when flood control measures were implemented to allow farming. Decades ago, landowners
saw ducks flock to these forests when they were flooded and saw the value to both
ducks and duck hunters in making this flooding more reliable.
Evidence now clearly indicates the challenge for landowners and forest managers is
to find balance. If land managers flood too soon or drain the water too late in the
season, tree roots can’t breathe and eventually die. According to Babst, some bottomland
forests have already suffered tree death because of years of constant flooding.
“During the last few decades, people realized that trees were dying in these GTRs.
These are forests flooded with the help of small dams to replicate what the hydrology
used to be before Europeans settled and built levees along many of the rivers and
streams in this region.”
The Arkansas Game and Fish Commission is funding the Arkansas Forest Resources Center
research project at the University of Arkansas at Monticello, in part with grant funds
from the Pittman-Robertson Wildlife Restoration Program of the U.S. Fish and Wildlife
Service. The research aims to determine the best conditions to flood GTRs and how
long the water can sit without doing damage to trees. This information will help inform
the AGFC’s ongoing efforts to ensure long-term, sustainable management of these limited
On this day, Kressuk’ s effort involved packing ice around seedlings growing in forest
wetlands. He measures the respiration rates — the emission of carbon dioxide — of
the roots from seedlings that were chilled by ice or exposed to ambient air temperature.
According to Babst, much is not known about root respiration in trees. But what is
known comes from research focused on roots during the growing season, not during winter
dormancy. His project involves exposing the roots of willow oak seedlings to decreasing
temperatures. His research team is trying to measure how and when root growth and
respiration change during the transition from fall to the dormant winter season. Babst’s
research tries to determine when root dormancy begins and ends and what kinds of conditions
must exist for dormancy to occur.
Those conditions may involve above-ground air temperatures, below-ground soil temperatures
and the species of trees being flooded. Some tree varieties handle the water load
better than others.
“When root activity and oxygen demand are low, we think the roots will be more protected
from the damage ordinarily caused by flooding, which reduces the amount of oxygen
available to roots,” said Babst. “If this is correct, and if landowners can time flooding
their forests more accurately, they may be able to provide habitat while doing minimal
or no damage to the tree roots.”
Babst said his research is made up of two different components, temperatures, and
flooding. The next stage is to test whether roots are more protected during winter
dormancy. His research team wants to know what happens to root activity during the
fall when changes in the day-night cycle and air temperature are happening.
“We had temperature controls on the soil. We used large 6-foot by 4-foot water baths,
each with chillers and heaters, to maintain the water temperatures. We then put potted
seedlings (housed in bags protected from flooding) into the water baths to maintain
“We had sets of plants that we eased into three different temperatures, 60 degrees,
50 degrees, and 40 degrees Fahrenheit. Soil temperatures here in Arkansas are typically
between 40° and 50° F during winter. Once those winter temperatures were reached,
we flooded half of the seedlings at each temperature.”
Babst said that most seedlings survived at all three temperatures, but trees in soil
maintained at 60° F showed significant fine roots death. He said the number of dead
roots decreased as soil temperatures dropped to 50° F, and there were virtually no
dead roots when soil temperatures fell to 40° F. The conclusion was that the lower
the temperature, the lower the root respiration, and more roots survived.
Babst said a lot of forestry professionals already suspected that the timing of flooding
is important. Still, it is crucial to have scientific data to support decision-making
in the field, where errors could be costly.
The key now, said Babst, is to find the right time to apply water to the forests.
He said narrowing down the best window of timing to start flooding green tree reservoirs
will require more research, but forest land managers now have something to hang their
decisions on instead of merely guessing.
Babst believes soil temperature has a more substantial impact for flooding than what’s
happening above ground. “Ideally, we would like to come up with a way for the forest
manager to take readily available weather data and plug it into a formula to determine,
‘Is it time yet?’” he said.
According to Babst, his initial experiments were done in a controlled greenhouse.
What made Kressuk’ s research special is that he took his experiments to the next
level. He moved his root respiration experiments into the field.
Babst said it’s inevitable that different results will be found in the field than
in a lab or greenhouse setting. “By manipulating the stem temperature and putting
a bag of ice around it, despite the warming air temperatures and plenty of sunlight,
does it slow down the respiration in roots by disrupting the phloem function?” Babst
“Phloem is like little pipelines through the stem that deliver sugars made by leaves
to roots,” Babst said. “Disrupting that flow of ‘fuel’ to the roots could slow down
root activity. If you look at a tree, it looks like it is not doing anything, but
it is quite active. If you dig up the root system, it will continue to do what it’s
doing, at least for a short period. Jonathan would then take those roots, clean off
the dirt, and put them in a chamber and measure the amount of CO2 the roots emit.
“It wasn’t surprising that we see respiration decrease with lower temperatures,” said
Babst, “We had a hypothesis, but now we have firm data. What AGFC and our research
partners want from this research is actual hard data. So, when they are making decisions,
they know they are making the best decisions that are supported by hard evidence.”
Babst partnered with researchers at the U.S. Forest Service Center for Bottomland
Hardwoods Research, Mississippi State University and Missouri Department of Conservation
to ensure what he learns applies broadly in the region.
Babst said this research is now in its third year, and he expects it to last at least
two more years. He adds that there hasn’t been much study of root respiration in southern
tree species, especially about the dormant season and flooded forests.
Babst said his greenhouse research so far indicates that the ideal time to begin flooding
bottomland hardwood forests is probably somewhere between late November to mid-December
to play it safe. To protect the trees, begin draining the water by the end of February.
More prolonged flooding killed many seedlings in the study.
“However,” Babst said, “if the low temperature is driving the changes in roots, rather
than declaring when the ‘right time’ is to flood, we should be identifying the right
temperature conditions. The weather is a little different each year, and so the date
when those conditions are reached could change somewhat from year to year.”
He said there are many variables to consider in the field. “This year, we saw a big
impact of freezing air temperatures. We need to keep looking to see if that effect
of a hard frost is consistent across years. And we need to narrow that window of time
when it will be safe to start flooding.”
About the College of Forestry, Agriculture and Natural Resources and the Arkansas
Forest Resources Center
The College of Forestry, Agriculture and Natural Resources, and the Arkansas Forest
Resources Center, a University of Arkansas System Center of Excellence, brings together
interdisciplinary expertise through a partnership between the University of Arkansas
at Monticello and the University of Arkansas System Division of Agriculture. The College
and Center are headquartered at the University of Arkansas at Monticello campus, but
their programs range statewide with the mission of developing and delivering teaching,
research, and extension programs that enhance and ensure the sustainability and productivity
of forest-based natural resources and agricultural systems. Academic programs are
delivered by the College of Forestry, Agriculture, and Natural Resources through the
University of Arkansas at Monticello. Through the University of Arkansas System Division
of Agriculture, research is administered by the Arkansas Agricultural Experiment Station,
and extension and outreach activities are coordinated by the Arkansas Cooperative
The University of Arkansas at Monticello and the University of Arkansas System Division
of Agriculture offer all of their programs to all eligible persons without regard
to race, color, sex, gender identity, sexual orientation, national origin, religion,
age, disability, marital or veteran status, genetic information, or any other legally
protected status, and are Affirmative Action/Equal Opportunity Employers.
About the Division of Agriculture
The University of Arkansas System Division of Agriculture’s mission is to strengthen
agriculture, communities, and families by connecting trusted research to the adoption
of best practices. Through the Agricultural Experiment Station and the Cooperative
Extension Service, the Division of Agriculture conducts research and extension work
within the nation’s historic land grant education system.
The Division of Agriculture is one of 20 entities within the University of Arkansas
System. It has offices in all 75 counties in Arkansas and faculty on five system campuses.
The University of Arkansas System Division of Agriculture offers all its Extension
and Research programs and services without regard to race, color, sex, gender identity,
sexual orientation, national origin, religion, age, disability, marital or veteran
status, genetic information, or any other legally protected status, and is an Affirmative
Action/Equal Opportunity Employer.
Media Contact: Lon TegelsU of A System Division of AgricultureArkansas Arkansas Forest Resources Center(870) email@example.com