Oak mortality workshop: what the experts taught us
A workshop titled 'Management for Oak Decline - A workshop for managing oak forests' was attended by over 100 forest managers in Grand Rapids on Oct 21st. The workshop was prompted by oaks dying across northern Minnesota over the past two summers. The epicenter of mortality is Grand Rapids where close to 12,000 acres of oak stands within a radius of fifteen miles have suffered crippling levels of mortality. The mortality is a result of drought, forest tent caterpillars, two-lined chestnut borers and Armillaria root disease. The workshop was developed by:
Tom Crow USDA-FS NCRS,
Dan Gilmore U of MN Forest Resources,
Julie Miedtke, U of MN Extension, and,
Mike Albers MN DNR Forestry.
Workshop presenters included:
Tom Crow USDA-FS NCRS,
Kurt Gottschalk USDA-FS,
Bob Haack USDA-FS,
Paul Johnson retired USDA-FS,
Dan Hanson MN DNR,
John Almendinger MN DNR, and,
Mike Albers MN DNR.
So what did the experts say about:
Oak management in general
- Oak management requires the evaluation and analysis of each stand. You can't use a 'cookie-cutter' approach.
- The best option for maintaining an oak component is to thin stands well in advance of significant stresses in order to develop vigorous oaks with large crowns.
- To be of any significant benefit, thinning has to release crop trees on at least three, and better yet, on all four sides of the trees? crowns. This is also called ?crown-touching? release.
- Thinning during stress events (such as severe drought or defoliation) adds to the stress which increases the amount of oak mortality. Kurt Gottschalk would disagree with this statement but hey- he isn?t here and he isn?t the one writing this article.
- In the Appalachians, Missouri and Arkansas, physiological maturity of oaks is estimated by dividing site index by stand age. When this figure is less than or equal to one, the oaks are vulnerable to decline or are already declining. Whether or not this holds up for oaks in Minnesota is yet to be determined.
Two-lined chestnut borers
- Branches and trees killed this past summer by two-lined chestnut borer will produce lots of adult borers next spring and summer and can spread the problem to new locations in firewood unless the wood is debarked or tightly covered with a tarp.
The situation in Itasca County and nearby counties
- Most of the sites with oak mortality around Grand Rapids have a ground cover of Pennsylvania sedge which will likely become denser as the stands open due to canopy tree mortality. This will be serious competition to any new oak regeneration on these sites and will have to be reduced somehow.
- The soils on these sites are very sensitive to compaction and even one pass of a skidder during frost free periods is likely to have significant adverse impacts.
- Most of the sites experiencing oak mortality have little or no oak regeneration. The regeneration that is on a few sites is too sparse and also too small to have a reasonable chance of survival. Also, stump sprouting will not occur when dead and declining trees are cut down due to the presence of Armillaria root disease.
- If you have an oak stand near Grand Rapids with high levels of mortality and want to maintain a significant component of oak in the future stand you will need to invest lots of time and energy doing so.
Planting oak seedlings
- Oak seedlings being planted need to have a stem caliper of at least 3/8 inch and better yet at least ? inch to have a reasonable chance of survival.
- Roots of oak seedlings being planted should be no longer than the blade of the planting tool being used to make the planting hole. Roots shouldn't be stuffed into the planting hole, rather, placed into the hole.
- Oak seedlings being planted on a site with an overstory survive better if the top of the seedling is cut back leaving only a 5" to 6" stub as a handle.
(Note: You could hear participants gasping for breath when Paul Johnson laid a bare root oak seedling on the blade of a planting bar and cut the root off to match the length of the blade. Several people may actually have passed out from hyperventilating when Paul next cut the top of the shoot off leaving only enough for a stubby handle.)
The main take home message was that waiting until the oaks start dying before beginning oak management is too late. By then you have lost most of your options and it will be much more difficult and expensive to maintain an oak component in your stands. So, if you want to maintain oak as a component of your northern hardwood stands, management needs to start at a young stand age. Aim at developing oaks with larger crowns and root systems in order to increase their vigor so that trees are more likely to survive severe stress events. And lastly, more attention needs to be given to developing advanced reproduction because most of our stands do not have any.