Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
3/1/99
Contacts:
David R. Coyle, Entomology Extension, (515) 294-1815
Elaine Edwards, Extension Communication Systems, (515)
294-5168
Yard and Garden Column for the Week Beginning March 5
Corn, Beans and Cottonwood Trees
by David R. Coyle
Graduate Assistant
Departments of Entomology and Forestry
Iowa State University
A common myth is that Iowa soil is good for only two things: corn and soybeans. However, these are not the only crops that can prosper within the state. Can you guess what another might be? No, I'm not talking about oats or alfalfa, although those do quite well. I'm talking about trees, cottonwood trees.
Short-rotation woody crop (SRWC) plantations are, in essence, large tree farms. They consist of a field of trees to be cared for and harvested just like any other crop. These are being developed and implemented by many large timber companies with much research supported by the U.S. Department of Energy. The entire tree can be harvested and used for paper pulp or biofuel energy. Trees in SRWC plantations also can be harvested for timber. In the northwest, SRWC plantations help decrease the harvest of old-growth forests, protecting acres of valuable wildlife habitat. Environmental stresses incurred by logging operations, such as soil compaction, erosion and pollution, also are decreased. SRWC plantations in Iowa could be planted in conjunction with riparian buffer strips to prevent erosion and runoff.
Cottonwood trees appear to have good potential for SRWC development in Iowa. These trees possess several desirable qualities including fast-growth, ease of regeneration and good growth form.
Many of the steps that go into a successful field crop are the same for a successful SRWC crop. The glaring difference is the time required for the SRWC crop to mature. This can be from seven to 30 years.
Like all crops, SRWC systems begin with field, or site, preparation. The best site for a cottonwood crop is a lowland or floodplain. Cottonwoods love sandy soil and lots of water. Once a suitable site has been determined, the soil is prepared by disking or plowing. Herbicides can be applied to control weeds. Cuttings or seedlings are then planted with a machine or more typically by hand.
During the first few years, one must take care of the site throughout the growing season just as one would for corn or beans. This may involve repeated disking, mowing or pesticide applications until the seedlings are tall enough to stay ahead of other nearby plants competing for water, minerals and most importantly, sunlight. This usually happens by the second or third year. After a number of years (usually seven to 10 for pulp or fuel biomass, or 15 to 30 for timber), the trees can be harvested with conventional logging equipment. Harvest in an SRWC plantation is much easier than in the forest because all the trees are the same age and can be harvested at the same time.
With the harvest complete, the site can be cleared of brush, disked and replanted.
By now you're asking yourself "Wow! Are there no downfalls to tree farming?" Unfortunately, this, like most other business ventures, has a catch. As the bean leaf beetle is to soybeans and the European corn borer is to corn, the cottonwood leaf beetle is to cottonwood trees. This beetle is the major defoliating pest of cottonwood trees in SRWC plantations in North America. Plants are the most vulnerable when young. During the establishment period (the first one to three years), leaves are very soft, have little waxy coating and are comprised mostly of water. Both the cottonwood leaf beetle larvae and adults feed on these leaves. Cottonwood leaf beetles can reach outbreak populations in young plantations. Like any other crop pest, if these insects are not controlled, hefty losses can result.
Feeding by the cottonwood leaf beetle causes the tree to lose leaves, the tools used to make food for growth. Without the leaves, the tree cannot grow to its full potential. This can cause loss in biomass over the long run, which will cost the owner a loss in dollars. One goal of timber production is to produce tall, straight trees with few branches. Cottonwood leaf beetles can damage the tips of branches so badly that the stem actually dies. This causes lots of branching, creating a bushy tree rather than a straight one. This too can cause a loss of dollars.
But don't be swayed by this pesky little beetle. There are many ways to control this insect. Lady beetles and lacewings are common natural enemies found all over Iowa. Insecticides are quite effective as well. Studies are underway to test the effectiveness of Bacillus thuringiensis, a type of bacterium, for controlling this insect pest.
SRWC plantations could do just fine in Iowa, and research plots at Iowa State University have shown just that. With the right site and care, SRWC plantations could be a valuable alternative crop. But, don't run outside, plow up the yard and buy seedlings just yet. There currently is no market for this crop in Iowa. Right now the only markets are found in the northwestern and southern states.
So, the next time you drive down an Iowa highway surrounded by fields of corn and soybeans, just think how nice it would be to drive through the shade of an Iowa plantation.
ml: isugarden
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