Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
12/16/02
Contacts:
Chris Feeley, Forestry, (515) 294-6739, cfeeley@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning Dec. 20, 2002
Adventures in Urban Forestry
By Chris Feeley
Extension Forester
Iowa State University
When people think about urban foresters, they consider them only as professionals to call when they are planting new trees or when their trees are in trouble. However, much of an urban forester's job is spent fixing mistakes. Those mistakes may have been made long ago because large trees often do not show stress symptoms for years after the problem.
Although Iowa is not known for large tracks of forests, we appreciate the trees we have and are willing to spend time and money to maintain and replant our trees. As an urban forester, I've traveled to many places looking at tree concerns.
Most of what I find tends to be common mistakes that are made when planting or caring for the tree. Once in awhile I find a situation that falls into my "Nightmare on Elm Street" file. Sit back, relax, and prepare to be horrified. To quote a famous television show, "The stories you are about to hear are real, the names have been changed to protect the innocent."
Oaks Exposed
A few years ago, I received a phone call from a resident concerned about
oak trees. The resident reported that about 20 mature oak trees wilted
and died within a short period of time. In addition, the trees had tested
negative for oak wilt and no construction had occurred on the property.
Perplexed at what could cause such mortality, I decided to visit the site.
When I approached the home I could see the brown leaves still attached to these at least 100-year-old bur oak trees. As I got closer to the home I noticed that the lower 10 feet of all the oak trunks appeared very pale.
The homeowner had recently returned from northern Minnesota where they had observed the art of peeling the bark off paper birch to make canoes. The homeowner then decided the rough bark on the bur oaks would be very useful in making craft items. The homeowner proceeded to remove all the reachable bark from the trees, in effect killing all 20 bur oaks.
So what went wrong? The bark performs the critical function of protecting the vascular system. The vascular system lies just inside the bark, and is the lifeline of the tree allowing for water, nutrients and sugars to be transported. Removing the bark essentially destroyed the vascular system and starved the tree.
To a Watery Grave
Last summer I received a phone call about mature trees that kept blowing
over and out of the ground with the slightest wind. In some cases the
leaves were a paler green with some of the new shoots wilting. In other
cases, the trees seemed very healthy and all the trees had tested negative
for diseases.
In this case the trees were excessively overwatered. In fact, overwatering is a big killer of trees. When the tiny air passages between the soil particles fill with water, roots cannot extract the oxygen needed to survive. In addition, the continually moist soil encouraged the root decay fungi that sped up the process.
With fewer and weaker roots, the trees were not able to stand up to the wind. Unfortunately, I think this may problem may be on the increase in Iowa. There are more lawn irrigation systems being installed, and the water needs of turfgrass are much higher than that of trees.
Depths Unknown
This next type of call is very common. A newly planted tree died quickly
with no signs of disease or insect problems. In most cases, the watering
and mulching were done correctly. What could have gone wrong?
Foresters and horticulturalists all over the United States are discussing the problem of planting trees too deep. Many people do not realize how crucial planting depth can be to tree health. In some cases the tree wilts quickly from lack of oxygen to the root system, similar to over-watering problems. In other cases, the tree hangs on for 15 to 20 years before symptoms of decline are observed.
The solution is simply to plant trees at the correct depth. When planting trees, remember to make the hole two to three times wider than the rootball and no deeper than the root collar. The root collar is where the trunk and roots adjoin and can be identified by a slight change of color in the bark and a swelling at the base of the trunk. This swelling will be different than the graft union, so it may be necessary to dig into the container or rootball to identify the root collar.
When tree questions arise, consult with your Iowa State University Extension county office or review the information on the ISU Forestry Extension Web site at http://www.forestry.iastate.edu/ext/ext.html. That way you can be sure to avoid the Nightmare on Elm Street file.
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