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Plants Reveal Secrets
Article #376, November 2025
By Bill Cook

Soil conditions and site productivity are major factors in determining which forest types best grow where.  Foresters employ various tools and decades of experience to help answer this question.  One such tool is “ vegetation or habitat typing”. 

    A sandy soil sits lightyears away from a loamy soil in terms of who might best grow where.  As the glaciers retreated over ten thousand years ago, they left in their wake a myriad of soil types, often a complicated hodge-podge.  Forest types are often keenly linked to that surface geology.  
    Three common tools are available to ascertain site productivity.  Each have advantages and disadvantages. 
    USDA soil surveys have been completed for most of the United States (a humungous effort!) and are now on-line at Web Soil Survey.  This service extends a wealth of information, if one can figure out how to access it.  Spending an hour or two on this web service can pay large dividends.  Voluminous paper copies may still be available at some offices of the Natural Resources Conservation Service.  Some counties have this paper copy also on-line.  Generalized Woodland Management recommendations exist for many soil series. 
    Secondly, foresters have long used “site index” research which uses tree species age and height data.  These data are used in one of a series of “site index tables” to render a predicted tree height at age fifty.  The higher the number (height), the better the site.  This practice works well as long as suitable trees are selected for measurement.  One must have a specialized tool called an increment borer and an accurate height measurement tool. 
    Third, and the focus of this article, is vegetation or habitat typing using key indicator species.  This system is based largely on understory vegetation, which often better reflects site characteristics and predicts which tree species are best suited to the site.  The understory species often persist even when the canopy has been, temporarily, converted from one type to another type. 
    However, many of the indicator species are spring ephemerals, somewhat limiting the time frame in which the evaluations can be carried out.  Yet, some habitat types are obvious.  Sandy outwash and an abundance of sweetfern and bracken means jack pine or red pine.  With more blueberry on site, then white pine might be considered. 
    To fully employ habitat typing, one must be able to recognize about 150 plants, and know their Latin names.  However, that number can be reduced by becoming familiar with the species more common to the forest types of interest, such as “northern hardwoods”. 
    Tim Burger and John Kotar spearheaded the field research used to assemble forest habitat types across different Lake States regions, such as the western Upper Peninsula.  Each region has a set of habitat types, usually a dozen or so.  A type has an acronym label based on the key understory species.  For example, “ATM” reflects “Acer-Tsuga-Maianthemum”, or more fully, Acer saccharum (sugar maple), Tsuga canadensis (hemlock), and Maianthemum canadensis (Canada lily).  Common understory species include sarsaparilla, Canada lily, bracken fern, starflower, bead lily and others. 
    The classification guides include dichotomous keys to help a user through the identification process.  At first, this can be frustrating but, with practice, becomes much easier as an experienced eye can identify the habitat type without the keys.  Once a type has been identified, the guide includes information about what trees should grow on what site and discusses advisable management practices, typical successional pathways, variants on the type, and more. 
    Most field foresters already have a pretty good “feel” for the relationship among understory plants and trees.  There’s a “vibe” that comes with experience.  That vibe has been articulated by ecology-based associations.  Habitat classification in the Lake States began around 1980 with Mike Coffman of, then, Champion International in the Upper Peninsula. 
    Habitat classification might have a rather steep learning curve, but the rewards of learning how various plant associations reveal secrets can be fun.  Identification is great.  However, knowing more about the community relationships is much better. 

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TRAILER- This website was created by a consortium of forestry groups to help streamline information about forestry and coordinate forestry activities designed to benefit the family forest owner and various publics that make up our Michigan citizenry.  This website is maintained by Bill Cook, Retired Michigan State Extension Forester/Biologist.  Direct comments to cookwi@msu.edu or 906-786-1575.