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Forest management: Expanding the gaps

ESCANABA — High quality sites usually have many management options for forestowners. For northern hardwoods, one such choice is an “expanding gap” harvest and reproduction system.

Northern hardwoods is the most common forest type in Michigan. A forest type is an association of a particular group of tree species, usually named for those that dominate the association. Sugar maple leads the pack in northern hardwoods, with variable mixes of red maple, basswood, yellow birch, hemlock, and many others.

High quality sites are described by certain soil properties, particularly soils that are nutrient-rich and well-drained. The retreating glaciers left us with a generous mix of landforms and young soil compositions. Blue cohosh, leatherwood, maidenhair fern, and Canada lily are a few of the plants that hint at these higher quality sites.

The owner of a quality northern hardwood stand on good soils is, indeed, a wealthy person. I define wealth not merely by stacks of coin hoarded in the local bank, but more by the appreciation of a wide range of management alternatives and complex ecologies. Knowing what you have is sometimes better than wanting what you don’t.

To better understand “expanding gap” management, it’s valuable to understand how it fits within forest science. So, let’s take a whirlwind tour.

The traditional management system to promote high quality sugar maple has been single-tree selection. Research on this began almost a hundred years ago in the Lake States, by a bunch of really smart guys. That legacy remains with us and it works.

This should not be confused with the crude “select cuts” where owners “cut the best and leave the rest”. Rather, single-tree selection gradually and artfully improves the quality of the stand of trees by removing the poorest trees first and balancing size classes. The forest responses are immensely rewarding.

Not all forest types do well with selection management. It has been specifically designed around northern hardwoods and trees tolerant of certain levels of shade. Alternatively, it’s a really good way to ruin a perfectly good aspen stand. Differences among forest types should not come as a surprise.

In recent decades, there have been some monkey wrenches thrown at single-tree selection.

Foresters have noticed an increasing domination by sugar maple, at the expense of other tree species that “ought” to be growing amid the palmate-leaved jungle. Single-tree selection intentionally promotes this “maple-ization”. Might single-tree selection work too well, at the expense of diversity?

Second, deer populations have increased across large regions of the Lake States to the point where deer prevent sugar maple (and other tree species) from becoming a new forest. This concerns foresters deeply. Yet, the love of deer has ingrained socio-cultural roots among many people with deep pockets.

Third, the changing climate and ever-more number of exotic species are changing the ecological rules of the Northern Hardwoods game. American beech is a poster-child example. Once a mainstay of many Northern Hardwood stands, exotic pathogens are driving beech into forest obscurity, as with so many other native North American tree species. These losses are disheartening.

So, foresters began scratching their heads and re-evaluating how to re-direct the natural processes that drive Northern Hardwood ecology.

Single-tree selection was actually pretty close to how Mother Nature applied her hand. However, some foresters figured that some of those holes in the forest canopy, that shone more light to the forest floor, that allowed knee-high trees to vigorously compete for that space, could be a bit larger.

Could the addition of larger gaps better enhance natural processes? What would happen if those larger gaps were built around species other than sugar maple? Would species like yellow birch and white pine have a competitive edge over the sugar maple? Or, would these richly regenerating gaps simply be garden salads for the voracious deer? Maybe the outcome would be nothing but brambles and Pennsylvania sedge?

The results, so far, have been mixed. No surprise there, either.

A twist on this “gap selection” scenario is “expanding gap” management. Larger gaps, maybe a half-acre, or as much as an acre or two, in size were scattered throughout the Northern Hardwoods. In another decade, or so, return to these gaps and harvest rings around them, kinda like a donut, maybe as wide as a hundred feet. Keep doing this until the gaps merge and the entire forest has been regenerated to conditions with different ages and physical structures.

Will the larger, more open, areas be able to move enough trees beyond deer browse heights to grow a new forest? What if lots of cut tops were left on-site as a physical barrier to deer? Will the tops last long enough for new trees to out-grow the deer?

Again, mixed results and with the jury still duking-out the verdict. The U.P. Land Conservancy has been watching progress on one of their working forests since 2008.

To better address this deer and forest regeneration quagmire, the Michigan DNR and MSU have recently emplaced a monster study in the northern Lower Peninsula and across the entire Upper Peninsula. There are 140 30-acres sites (over 4000 acres) with a mix of treatments to help figure-out how Northern Hardwoods might be managed in the face of high deer densities. It’s an aggressive ten-year research project that might easily last longer. There are some very clever people guiding this huge freighter, and the holds are filling with volumes of data.

One might ask, why not simply use the do-nothin-and-let-nature-take-its-course scenario? We know that’s not working across much of the Lake States. These forests are not regenerating. Tree diversity is decreasing. Neither the current forest compositions nor the high deer populations are “natural”. Both are human-caused after a 150 years of landscape occupation. Management can reset this compass, to a certain degree.

There are two species that can affect the long-term trajectories of forest ecology; human beings and white-tailed deer. Only humans can make a choice for a better future. Deer can only eat their way into oblivion.

The exploitive logging and rampant wildfires of a hundred years ago have left us with the forests that we have today, in which foresters have worked to manage in order to provide as many products and services as possible. Forest management can restore some of the forest characteristics lost during the Paul Bunyan years and, maybe, compensate for the damage that deer impart.

Our grandchildren, or great-grandchildren, will be the heirs of our decisions, or lack of decision.

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As an MSU Extension forester, Bill Cook provides educational programming for the entire Upper Peninsula. His office is located at the MSU Forest Biomass Innovation Center near Escanaba. The Center is the headquarters for three MSU Forestry properties in the U.P., with a combined area of about 8,000 acres.

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