Stem Girdling Roots (SGR’s)
and The Rest of the Story
By Richard J. Hauer
Photos by Richard j. Hauer
Stem Girdling Roots (SGR’s)
Hello Americans, this is not Paul Harvey. You know what the news is. In a
minute (seven paragraphs to be exact), you’re going to hear ... the r-r-r-rest of the
story!
Page One. In 1994, Northfield, Minnesota, a crisis is brewing in the urban forest.
Something is amiss with the urban trees. Norway maple trees are showing signs of old
age, yet they are in their teens and twenties. They are just mere teenagers and young
adults of the tree world and they are showing their ills through wilting and scorched
leaves and the striking dieback of twigs and branches in the canopy (Figure 1).
Could it be as simple as Verticillium Wilt, the disease caused by the soil-borne fungi
such as Verticillium albo-atrum and Verticillium dahliae? Verticillium wilt produces
symptomomatic wilting and scorching in the canopy of the tree and discoloration of
the wood xylem in cross-section. Folks, these trees certainly were showing signs of
wilting and scorching in the canopy. Hopefully, a simple verification by leading tree
experts would put this story to rest and solve the mystery.
Cindy Ash and Gary Johnson enter the picture. Both are trained in classic tree
pathology and understood how to diagnosis the tree patient in situ among their urban
forest friends. Each knows their way around a Petri dish as much as they know their
way around the urban forest. But something was wrong with a diagnosis as simple
as Verticillium Wilt. The wilting of leaves in the canopy was not like that caused by
Figure 1. A healthy Norway maple tree and one showing severe decline from
stem girdling roots.
ADVOCATE • Winter 2007
Photos by Richard j. Hauer
Verticillium. And what about staining in the wood xylem? What staining! None was
found in the trees that these arboreal masters touched and examined. Even more,
something was strange as these trees had stems that looked more liked telephone
and telegraph poles coming out of the ground, rather than the normal tapering of
stems that deciduous trees from the angiospermous world so commonly exhibit.
Lucky for us, Cindy and Gary had a tool. Oh yes, a tool that each and every
one of us has learned to master at some point in our life. A tool that we call a hand
trowel. Upon digging and removal the soil to expose the magnificent underworld
of the tree, they observed something abnormal. Abnormal is just the opposite of
normal and one must understand what is normal to determine what is abnormal.
Roots radiating away for the central stem like spokes on a wheel is normal and
what a tree is genetically trained to do from life within the first several days as a
germinating seed and weeks later as a growing seedling (Figure 2). But these trees
had something new, something different or abnormal. They had roots circling
around the stem (Figure 3). In some cases, this fortuitous finding by the simple
removal of soil and exposure of the roots led to not one but several roots wrapping
around the stem. Even more so with several trees, there were layers of encircling
roots as the depths beyond the surface was explored. Would this be the end of the
story?
Figure 2. A normal stem and root system
juncture on a Norway maple tree.
Figure 3. An abnormal root system
encircling and compressing the stem of
a Norway maple tree.
Now for Page Two. Gary and Cindy left that day with questions. Was this
an isolated case of a few trees gone bad? Or was this something even bigger?
The only way to find out was to apply principles first taught to us in elementary
school and later honed in middle and high school, possibly even in college and
as a professional - science. The scientific process involves making observations
and recording them. Document what you see and compare this to what is already
known. From this we make conclusions. Well, Professor Johnson did just that.
First, the records of those trees in Northfield were noted. Then more observations
were taken from the trees within the urban forest of the Minneapolis and Saint
Paul metropolitan region. Tens, then hundreds, and eventually over a thousand
observations were recorded. The presence or absence of encircling and girdling
roots, depth to the structural roots that radiate away from the stem, diameter and
species of tree, and recording on the general health of the tree was noted.
These scientifically based observations led to a discovery: buried root systems
are not good for trees and tree roots systems buried by soil can become short-lived
trees. Not every case of buried root system led to a tree becoming ill at a young
continued on p. 10
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Stem Girdling Roots continued from p. 9
age. Heck, even the urban forest has George Burns trees that push the envelope
on biological tolerance. But many trees with buried root systems did start dying
young.
With these findings in hand, a technology transfer grant was received from
the Midwest Center for Urban & Community Forestry to disseminate these
observations to the practitioners who foster the urban forest. But what to name
the publication? Developing a title is often as hard as developing the introductory
paragraph. Especially with a quandary of terms such as girdling roots, girdling
root syndrome, strangling roots, encircling roots, embedded roots, partial girdling,
root strangulation, root tangle, root spiraling, coiling root, root malformation,
deformed root systems, root deformation, and others competing for entry as title
winners.
It was the morning of a brisk day in March 2000 and the caffeine from
copious amounts of coffee were doing their work when, at the same time, it
struck Gary Johnson and myself (I was working as a graduate research student
with Professor Johnson at the time) that the problem was from a root contacting
and compressing the stem. From that elegant postulation came the new term,
Stem Girdling Roots or SGR’s for short. Why the new term SGR’s? It seemed to
adequately define the problem. The problem occurred when root tissue connected
with and led to stem compression and anatomical dysfunction with smaller
cells and their arrangement into tissue. This manifested itself into physiological
reductions in the transport of water and manufactured food. Further, defining the
location on the plant where the pathological agent (the root) was causing its harm
was consistent with the description given to insect and disease caused ailments
(e.g., bark borer, twig girdler, root rot, flower blight).
Now Page 3 and the Rest of the Story. The message is simple. Nature knows
where the roots of trees should be and following these cues is one important step
in the right direction. Roots of trees are near the surface and a normal stem taper
and directional movement of roots away from the stem at the soil surface is a
guarantee with genetic backing from the arboreal gene pool. Practitioners and lay
people alike are getting the message and moving the urban forest forward one
root system at a time.
But this is not the first discovery of the harm that can come from burying
tree root systems. Nearly four centuries ago, a similar observation led William
Lawson to remark in 1618 in A New Orchard and Garden, the tree care text of
his day, that “most functioning roots were near the surface … and injury would
result if these were buried.” And now you know the rest of the story—to plant at
grade—good day!
Richard J. Hauer is an Assistant Professor of Urban Forestry at the University of Wisconsin – Stevens
Point. You can reach him at [email protected] or 715-346-3642
For more information on buried root systems and SGR’s, see A Practitioner’s
Guide to Stem Girdling Roots of Trees at (http://www.extension.umn.edu/distribution/naturalresources/DD7501.html) or the Fall 2000 (vol. 3, no. 4) of the
Minnesota Shade Tree Advocate.
ADVOCATE • Winter 2007