agroforestry question

Joseph Zorzin redoak at
Thu Dec 9 05:59:29 EST 1999

TREEFARMER at wrote:

> Iowa State Extension had a chart and short explanation that was
> published in a farm journal about 15-20 years ago. Basically it showed a
> decrease in yield next to the windbreak and and an increase in yield
> about 3-5 tree heights out in the field. The increase more than offset
> the decrease.
> Our tenant has a yield monitor with GPS map making capabilities. These
> new tools will greatly enhance research in this area. We have found
> yield decreases next to timber areas even after root pruning. Other
> areas don't have yield losses. My feeling is that losses are due to
> water shedding by the trees which inundates the edge of the field.
> Shading doesn't seem to be a factor. Trees with light canopies like
> Black Locust don't seem to affect the crop.

I would think the cause of the decrease is because the trees are sucking up
the water- and drying out the ground near the crops. Trees can pump a great
deal of water out of the ground- not just the water they use- it just goes
into the atmosphere and this process is known as "evapotranspiration" (sp?).

I should think the effect would also depend on the type of crop.
Joe  Zorzin
Massachusetts Licensed Forester #261

Member of Forest Steward's Guild

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