Progress on the Big Northern Hardwoods Study
By Bill Cook, MSU Extension Forester/Biologist
The “Big Northern Hardwoods” study is one of the largest forest research efforts in history. The major set of questions have to do with forest management techniques that might result in new forests in the face of long-term heavy deer browsing. No small task.
Large portions of Michigan forests have experienced decades of “recruitment” failure, mostly due to intense browsing pressure by deer. Foresters use the term “recruitment” to describe new trees that reach sapling size, which is beyond the reach of hungry deer.
“Regeneration” is new trees, either seedlings or sprouts, that have yet to run the gauntlet of deer browsing. For the most part, regeneration goals encouraged through forest management have been successful. The challenge has been getting enough of these young trees into the “recruitment” size class.
So, the Michigan DNR and Michigan State University teamed-up to create a large-scale design to test three management scenarios in the Northern Hardwood forest type (dominated by sugar maple), over a period of ten years. The three harvest techniques deployed are seed-tree, shelterwood, and large gaps. As a “control”, traditional single tree/small gap silviculture has been used, too. Across the Upper Peninsula and the northern Lower Peninsula, 140 30-acre sites were identified. That’s over 4000 acres of experimentation!
The seed tree method, unusual for Northern Hardwoods, is essentially a clearcut, except for six to eight quality trees per acre. The shelterwood method removes 50-60 percent of the overstory, leaving partial shade to “nurse” along new regeneration. Variations of gap management have long been a Northern Hardwood management option, but gap sizes used in this study are rare, ranging from 0.3 to 1.0 acre in size. Historical gap sizes were generally under a tenth of an acre.
All sites have been commercially harvested and 2019 concluded their second growing season.
In addition to overstory harvests, about half of the sites had tree tops (slash) left on-site to provide physical barriers to deer. Hopefully, the tops will last long enough for regeneration to move into recruitment size class.
The other half of the sites will receive herbicide applications followed by scarification (mineral soil exposure) treatments in 2020. This treatment is intended to decrease undesirable legacies of deer browsing and selection silviculture (e.g. beech and ironwood saplings) and improve germination and growth environments for a diverse mix of tree species.
Wildlife cameras were placed at 48 sites. To date, the camera “harvest” has produced nearly 800,000 images. University researchers are using “machine learning” to have a computer identify deer from these images. Technicians will then take a more detailed look at these images to describe deer residence time (how long the stayed in front of the camera) and behaviors. Technicians replace batteries and SD cards on four month rotations and move cameras to new sites annually.
This past Summer and Fall, a crew of a dozen forestry technicians collected vegetation data from the study sites. With measurements taken before harvest, and then one, five, and ten years after treatments, the responses of tree regeneration to silviculture treatment, deer use, and other factors will be determined. Over the study years, the best outcomes (diverse, well-stocked regeneration of desirable tree species) will be identified and adapted by forest managers.
For the most part, public reaction to these research plots has been positive. Cutting firewood from the retained tops has, perhaps, been the most common question.
This long-term study is being conducted in cooperation with Michigan State University, the Michigan DNR, the forest products industry, and Safari Club International, Michigan Involvement Committee. For more information, contact Gary Roloff (roloff@msu.edu) or Mike Walters (mwalters@msu.edu).