UPPER PENINSULA NORTHERN HARDWOOD FOREST TYPE

Northern hardwoods have been the most common forest type in Michigan for centuries, and are becoming more so as natural succession gradually converts many stands to this shade tolerant association.  Northern hardwoods are not “just hardwoods that grow in the north”.  In Michigan, the term specifically applies to stands dominated by sugar maple.  Associates are shade tolerant trees, including some conifers.  When sun-living species are present (e.g. aspen, paper birch), they were established after the prior stand was killed and more sunlight was available. 

High quality logs, especially sugar maple, command some of the highest prices in the region.  Low quality material makes excellent pulp for paper-making, where markets are available. 

How are forest types defined?  Click here for an explanation.

The Trees

Sugar maple, red maple, hemlock, yellow birch, and basswood are the most common trees in the Upper Peninsula northern hardwood (NH) forest.  The maples, alone, account for over half the volume in the forest type in the U.P.  Typical secondary species are quaking aspen, beech, balsam fir, cedar, and black cherry.  Later successional trees of the NH type have the ability to reproduce themselves under the shade of the forest canopy.  The ability varies with species, but sugar maple is, perhaps, the most shade tolerant.  Shade tolerant species usually have longer life spans. 

The composition of NH stands varies widely, based on seed source, soil type, water conditions, past history, etc.  There are several northern hardwood variations; such as sugar maple-beech-yellow birch, sugar maple-basswood, sugar maple-beech, and others.  In the western Upper Peninsula, beech disappears from the forest.  In southern Michigan, central hardwood species appear.  Northern hardwoods contain Michigan’s single largest component of hemlock and white pine.  The maples are most noted for their beautiful fall colors.  They comprise over a quarter of all the forest volume in the state and continue to grow in abundance and size. 

Distribution

NH stands occur from Minnesota/Manitoba to New England/Maritime Provinces, with a band running down the Appalachian Mountains.  Some of the best developed and largest blocks grow in the Upper Peninsula and New York. 

Ecology

The northern hardwood type has the highest level of tree diversity in Michigan, especially in the southern Lower Peninsula where central hardwood species blend in.  A good share of the NH type tree diversity also comes from species common to earlier successional stages that persist in the stand.  Generally, these species are shorter-lived and, over time, will drop out of the composition.  Eventually, sugar maple tends to dominate NH stands because new seedlings can survive lower light levels and roots can penetrate leaf layers.  Most other tree species require ground disturbance and more light.  This dynamic is why many ecologists label NH stands as the successional “climax” on many sites.  

Much of Michigan’s NH type is even-aged, primarily due to past cutting practices.  Management practices and natural succession trend toward an increasing amount of uneven-aged forest.  Relatively small gaps in the forest canopy provide the major mechanism for the natural reproduction of NH species.  Gaps are created by the death of large dominant trees or groups of trees.  Higher levels of disturbance generally promote greater tree species diversity.  Northern hardwoods are fairly fire resistant; although records show a history of rare stand-replacing wildfires. 

Management & Silviculture

Northern hardwoods can be managed using either even-aged or uneven-aged systems.  On better sites, uneven-aged management is typical using the selection system (incorrectly called the “select” system or “select” cutting).  A range of diameter classes is “marked” for removal in order to achieve a prescribed balance of size classes.  The level of light plays a key role in the natural reproduction and growth rate of NH species.  Stand density (the combination of tree size and number of trees) determines the amount of light available within and below the canopy.  Stand density is measured using the number of square feet of tree trunks per acre.  This is called “basal area”.  Thinning stands on a 10-15 year cycle is typical, with the objective of manipulating stand density to maximize tree growth, health, and quality.  A thinning prescription or harvest can vary widely.  The services of a professional forester are especially important to balance stand capability with landowner objectives.

Single-tree selection creates many small gaps and generally favors sugar maple.  Group selection creates larger gaps to encourage regeneration of more tree species, especially when mineral soil is exposed.  However, gaps too large may result in heavy brush that might impede tree reproduction. 

Thinning operations need to be carried out by experienced loggers.  A good logger will provide good service with any kind of harvesting system, from horses to large cut-to-length processors.  Special care needs to be taken to avoid damage to the residual stand.  Ruts and soil compaction should be avoided.  Winter logging will often eliminate negative soil impacts but will seldom expose mineral soil needed by many trees for regeneration.  Timing of operations should be discussed with a forester. 

On poorer sites, clearcutting or shelterwood systems may be more desirable.  Where NH types grow poorly, conversion to another forest type should be considered. 

Maple syrup production is a management option.  Crop trees and future crop trees should be given enough crown space to grow without competition.  Large-crown trees will produce more sap.  Keep in mind that the wounds from taps will introduce defect and stain, rendering a low value log.  A sugar maple tree can provide either syrup or a quality log, but not both. 

Tree Health Issues

Northern hardwoods are host to a large number of insects and diseases, but serious damage is uncommon.  Forest tent caterpillar (Malacosoma disstria) populations reach epidemic levels on a 10-12 year cycle.  The sugar maple borer (Glycobius speciosus) may be the most serious insect pest of sugar maple.  Other common damaging insects include the fall cankerworm (Alsophila pometaria), spring cankerworm (Paleacrita vernata), gypsy moth (Lymantria dispar), bronze birch borer (Agrilus anxius), and some aphids and scales.  Common diseases include Armillaria root rot, Eutypella and Nectria cankers, brown and white rots, and Anthracnoses.  Beech bark disease, a combination of a “scale” insect and several fungi, will have major impacts on the beech component of NH stands.  High populations of deer, porcupines, squirrels, and rodents can seriously impact regeneration and survival of trees.  Invasive species such as buckthorn, garlic mustard, ironwood, and Pennsylvania sedge can overtake an area precluding forest regeneration, especially in heavily browsed areas.  Along with the emerald ash borer and gypsy moth, a number of exotic pests will likely threaten NH forests in the future. 

The best defense against natural and exotic insects and diseases is a stand of healthy trees.  High tree vigor, achieved through good management, will reduce the impact of tree stressing events.  Northern hardwood species growing on less desirable sites will be more readily impacted by drought, wet seasons, and other weather-related events. 

Wildlife Habitat

Northern hardwood stands are host to a wide range of wildlife species, but are not heavily used by most game species, such as deer, grouse, turkey, and woodcock.  Many species of “neotropical migrants”, or migrating forest birds, utilize NH forests. 

Maintaining nut-producing trees can be important.  This “mast” provides food for many species.  It is a good idea to leave 6-8 large “snags” per acre for cavity-nesting species such as woodpeckers, flying squirrels, wood ducks, owls, and others.  A few large logs per acre rotting on the ground provide habitat for other groups of wildlife, such as salamanders and food sources for bears.  Conifers in NH stands offer protection from harsh weather.  Small spring ponds (large puddles), springs, rock outcrops, and other interesting elements should be protected.  This might mean a limited harvest or trail rerouting.  Group selection will likely increase the number of wildlife species in a stand.  Forests along lakes and streams are particularly important for wildlife corridors.  They often experience use by a high number of species.  Steep slopes need to be considered in harvest operations due to erosion potential.  

Well-managed NH stands are sometimes mistaken for “old growth” stands.  On public lands, these stands are sometimes placed in “old growth” management programs, where timber harvest is restricted or eliminated.   

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This site created and maintained by Bill Cook, MSU Extension Forester for the Upper Peninsula of Michigan, now retired.  He continues to respond to suggestions, questions, and corrections. Contact him at cookwi@msu.edu.