Tree Diversity by Forest Type

There are many ways to categorize differences within the forest. One of the more commonly used classifications is that implemented by the U.S. Forest Service in their Forest Inventory and Analysis Unit (FIA). In Michigan, there are 15 forest types labeled according to their dominate tree species. Species diversity varies naturally between forest types. Human influence has also impacted species diversity. Tree species diversity may, or may not, reflect the diversity of plant forms, but might serve well as a preliminary indicator. Lastly, the FIA figures are for each forest type on a statewide basis. Every stand of trees belonging to a particular forest type will not display the same level of diversity as other stands within the forest type. Geography, stand history, soils, water, and other factors create variability within a particular forest type.

Acreage and Number of Tree Species Recorded in the Forest Types of Michigan
Forest Type	Acres	#Species	Forest Type	Acres	#Species
Northern Hardwoods Oak-Hickory Elm-Ash Cottonwood Aspen Red Pine Northern White Cedar Paper Birch Balsam Fir	7,161 1,982 1,627 2,676 897 1,349 292 563	71 63 57 50 40 36 35 32	White Pine Scotch Pine Balm-of-Gilead Jack Pine White Spruce Black Spruce Tamarack	234 147 190 846 147 465 149	32 32 27 26 25 22 22
Source: FIA data, 1992

The forest type with the highest number of tree species is the northern hardwoods, typified by maple, basswood, beech, and yellow birch. Seventy-one tree species have been recorded within northern hardwood stands across Michigan. It is the most common forest type in Michigan and continues to become more common as time passes. The northern hardwood type is generally at the later stages of forest succession.

The forest types with the least number of tree species is tamarack and black spruce. These stands tend to be highly dominated by either tamarack or black spruce, with 21 other species occurring. These stands typically grow on wetland sites where fewer tree species can survive. However, these two species grow in many different forest types, as we'll examine further down this page.

The simple number of tree species is only one way of looking at diversity. The idea of "species richness" is important, too. Richness has to do with how dominant a few species are. For example, two stands may each have 1,000 trees of 25 tree species. In one stand, each species may have an equal number of trees, or 40 trees per species. This would be a species "rich" stand. The second stand may have 5 species that have 100 trees each, and the remaining 20 species have only 25 trees each. This stand would less "rich".

If we look at Michigan's 15 forest types using a tree species richness measure, the most diverse forest type is swamp hardwoods (elm-ash-cottonwood). The least diverse type would be jack pine.

Tree Species Richness in Michigan Forest Types
Forest Type	Five Most Common Tree Species	Percent Volume of Top Five Species
Elm-Ash-Cottonwood Northern Hardwoods Balsam Fir Paper Birch Aspen Oak-Hickory White Spruce Black Spruce White Pine Scotch Pine Northern White Cedar Balm-of-Gilead Red Pine Tamarack Jack Pine	Red Maple, Silver Maple, Black Ash, Green Ash, Cedar Sugar Maple, Red Maple, Basswood, Hemlock, Beech Balsam Fir, White Spruce, Quaking Aspen, Cedar, Paper Birch Paper Birch, Red Maple, Quaking Aspen, Cedar, Balsam Fir Quaking Aspen, Bigtooth Aspen, Red Maple, Paper Birch, Balsam Fir N.Red Oak, White Oak, Black Oak, Red Maple, Bigtooth Aspen White Spruce, Quaking Aspen, Paper Birch, Balsam Fir, White Pine Black Spruce, Tamarack, White Pine, Balsam Fir, Cedar White Pine, Red Pine, Red Maple, Quaking Aspen, Paper Birch Scotch Pine, Red Pine, Black Cherry, White Pine, Balm-of-Gilead Cedar, Balsam Fir, Paper Birch, Red Maple, Black Spruce Balm-of-Gilead, Cedar, Balsam Fir, Quaking Aspen, Paper Birch Red Pine, White Pine, Jack Pine, N.Red Oak, Red Maple Tamarack, Cedar, Black Spruce, White Pine, Balsam Fir Jack Pine, Red Pine, N.Red Oak, White Pine, Quaking Aspen	58 64 69 75 75 76 76 77 78 81 82 86 90 91 93
Source: FIA data, 1992

Yet another way to look at forest tree diversity is the species distribution across different forest types. For example, sugar maple, beech, and basswood are largely restricted to northern hardwood stands. They are seldom found in other forest types. On the other hand, most of the white spruce volume is not found in white spruce stands. The following table shows how much volume of a particular species is found within its "typical" forest type. Species with high percents may be good indicators of a single forest type. Species with low percents are not very good indicators, but have the ability to survive across a wide spectrum of site conditions and forest associates. This concept is commonly used to identify understory species, particularly wildflowers, that can be used to indicate certain site conditions and productivity. Wildflowers are frequently better indicators than trees.

Forest Type Association Preferences for Common Michigan Tree Species
Species	Forest Type	Percent of Volume in Forest Type	Species	Forest Type	Percent of Volume in Forest Type
Sugar Maple Beech Basswood Hemlock Yellow Birch Silver Maple Red Pine Black Oak White Oak White Ash Jack Pine Black Cherry Cedar N.Red Oak Scotch Pine	Northern Hardwoods Northern Hardwoods Northern Hardwoods Northern Hardwoods Northern Hardwoods Swamp Hardwoods Red Pine Oak-Hickory Oak-Hickory Northern Hardwoods Jack Pine Northern Hardwoods Cedar Oak-Hickory Scotch Pine	95 95 89 87 85 83 79 78 77 76 73 71 70 65 65	Red Maple Cottonwood Bigtooth Aspen Green Ash Quaking Aspen Black Ash Black Spruce Tamarack Balm-of-Gilead American Elm White Pine Paper Birch Balsam Fir White Spruce	Northern Hardwoods Swamp Hardwoods Aspen Swamp Hardwoods Aspen Swamp Hardwoods Black Spruce Tamarack Balm-of-Gilead Swamp Hardwoods White Pine Paper Birch Balsam Fir White Spruce	61 60 57 56 55 54 46 34 32 31 27 23 23 15
Source: FIA data, 1992, for tree species with at least 100,000 cubic of volume in Michigan.

	This website was developed and created by Michigan State University Extension for the teachers of the State of Michigan. The website is maintained by the Delta-Schoolcraft Independent School District in support of the Michigan Forests Forever CD-ROM from the Michigan Forest Resource Alliance.

Page Name: TreeDiversity.htm
Please provide comments to Bill Cook: cookwi@msu.edu or 786-1575