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What i did on
my Summer Vacation
or
Doing Hard Time at the Old Pen
"A Study of
Tree Roots" |
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I have spent
many years observing the above ground portion of
trees and other plants in an effort to better
understand how and why they grow (or not grow, as
the case may be) in the widely variable locations
that we humans and also Mother Nature plant them.
So it has been an unusual treat for the past two
weeks to have an opportunity to observe the below
ground portion of a fairly diverse group of trees
growing on a rather harsh site in south central
Wyoming.
The
opportunity arose as part of a project to install an
underground irrigation system at the Wyoming
Frontier Prison in Rawlins, Wyoming—affectionately
known to long time Rawlins |
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First, most tree
roots are surprisingly shallow—even those of some
trees considered to be drought tolerant. The roots
of Russian olive and cottonwood appeared to be
mostly within the top 18 inches of soil and most
within the top 12 inches. And their root systems
are dense and extensive. It would appear that these
“drought tolerant “ trees have developed that
capacity more by stealing water from other plants in
the landscape than by actually conserving water. A
trench passing 35 feet from a small grove of
Russian olive trees and
one old cottonwood was exposed one inch diameter
roots every 3-4 inches—and all only 6-8 inches
deep. |
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April 27, 2006
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residents
as “the Old Pen” (short for penitentiary)The
Frontier Prison was originally built in the late
1800’s, even before Wyoming became a state. A newer
facility was built in Rawlins in the mid-1980’s so
the “Old Pen” was shut down in 1986. It sat empty
for a few years until a group of Rawlins citizens
took the initiative to have the facility added to
the National Registry of Historic Places and turn it
into a museum. Its history documents almost a
century of the less seemly side of the state’s
social and economic development. The site includes
a cemetery grounds in which are buried prisoners who
died while incarcerated and a number of prisoners
who were executed, some by hanging. Some local
residents claim that both the cemetery and the old
prison facility are haunted.
The 10+
acres of landscaped and minimally maintained grounds
which surround the actual prison facility contains a
rather diverse variety of mature trees which the
staff and board of the historic site were anxious to
protect from any unnecessary root damage during the
installation of the irrigation system. The routing
of main irrigation lines had to be done in such a
way as to minimize root damage to existing trees
while still providing a state of the art irrigation
system.
So I ended
up spending several days over the past two weeks on
a small backhoe carefully (as possible) digging
trenches in fairly close proximity to mature
cottonwoods, American elms, green ash, rocky
mountain juniper, hackberry, Colorado spruce, downy
hawthorn, Russian olive, and an occasional
willow—and inevitably digging up quite a few roots.
The appearance of roots varies widely by species, by
the way, so its quite easy to distinguish the roots
of a cottonwood from a green ash or a Russian
olive.
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The local city arborist was
most concerned about not doing harm to the sites
remaining American elms. There are about 20 of
these once widely planted landscape trees still
surviving on the site. The main sprinkler line was
specifically routed to avoid these trees, yet I
still dug up a number of American elm roots—once
almost 80 feet away from the nearest American elm.
It would appear that these trees developed their
drought tolerance by developing roots capable of
extending far from the tree in search of water and
soil nutrients. Not surprisingly, these roots would
generally be 12-18 inches deep.
I’m not sure I learned anything
about green ash from the experience. This is a tree
that has puzzled me for years, because it has a
reputation for both drought tolerance and soil
adaptability, but in my experience, and the
experience of a number of other landscape managers
around Wyobraska, this tree has neither. I remain
convinced that the green ash is more of a “forest
tree” than a “prairie tree”. The several surviving
green ash on the Frontier Prison site are all
located in areas that have been historically
irrigated on a regular basis, and most of those are
in poor health. Their roots appeared to be larger,
less numerous, and deeper than those of the other
trees on the site—all qualities of the root systems
of trees common to forests.
The site contains a number of
groves of juniper trees, although the irrigation
system did not pass close enough to these
demonstrably drought tolerant trees to be able to
add anything to my understanding of their root
systems. I have dug enough of them out of
landscapes, though, to know that their root systems
tend to be layered—a rather unusual phenomenon among
root systems--one which they share with ponderosa
pine, another superbly drought tolerant tree.
Roots are not the most
ornamental part of the plants they serve, but they
are crucial to the health and appearance of the
plants. For many years now I have been convinced
that the first question to ask whenever there is a
problem with a tree should be “What’s wrong with the
roots?” After doing a little hard time at “the old
pen” this summer, I am more convinced than ever that
this is so.
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