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RUNNELS, Iowa - It was a good half-mile hike back to the 40-acre section of timber on the Red Rock Wildlife Area that gave Jeremy Cochran and Todd Gosselink time to explain their plans to improve the forest resource on this heavily used public area.
“It’s a common misconception that the way to manage a forest is to leave it alone. Leaving it alone is a management choice, but it is one of the factors leading to oak decline in Iowa,” said Cochran, district forester with the Iowa Department of Natural Resources (DNR) Wildlife Bureau. “What we specifically did here was a crop tree release. We identify which tree species to favor based on the goals for the timber, and then release it from the competition.”
In this section of Red Rock’s Walnut Creek Unit, walnuts, hickories and oaks are the favored species. From moths and butterflies to flickers, pileated woodpeckers, squirrels, turkeys and deer – Iowa wildlife depends on oaks. And of all the oak species, the white oak is the most preferred because of its more palatable acorn. The amount of white oak acorn production varies over 3-5 years and during the years when production is down, red oak and bur oak acorns fill the need.
On this ridge overlooking Lake Red Rock, the signs of a crop tree release project are everywhere. Crop trees to keep are sprayed with orange paint; the nonnatives and non-target trees have two cuts around the trunk about a foot apart.
The process follows the same script – step one is to write a timber plan about a year in advance, walk the section and mark the crop trees to save, and then non target trees are eliminated using a method called girdling or felling. Girdling is where the tree is cut through the sap-wood of a tree, but not completely through, to sever the connective tissue and sap flow.
Although the tree is dead, it can be up to two years before it succumbs to the girdling. The tree is allowed to remain standing to provide valuable habitat for woodpeckers and, later, for bats.
There are times when oaks, walnuts or hickories are cut in the crop tree release because there’s either not enough diversity among the nut producers or the timber stand is too crowded and the foresters have to make a choice.
The ultimate outcome of the crop tree release is to thin the canopy and allow more sunlight to the crown of the trees which can increase nut production up to seven fold and can double the annual diameter growth.
“By improving the vigor of trees, we can improve the overall health of the forest,” Cochran said.
A contractor can double girdle about five acres of trees per day. Much of the timber management is done after the hunting seasons close and before the dormant season ends.
While Gosselink and Cochran were focused on 40 acres of the Red Rock Wildlife Area, more than 2.2 million forested acres in Iowa is in private ownership. Cochran said foresters with the Iowa DNR are available to meet with landowners, walk the timber and put together a management plan to improve the overall forest health. Local forestry contractors are important to help execute the improvements.