Forest inventory

How is it that foresters know how much forest is in Michigan?

How is it that foresters know how much forest there is in Michigan?

The data comes from an inventory system that has been ongoing in Michigan since 1935. Collection of that data involves a lot of field sampling and statistics. There are no better data sets to describe Michigan’s forest resource. Statewide periodic inventories were published in 1935, 1955, 1966, 1980 and 1993. In 1999, the inventory was “annualized” with a fifth of the plots re-measured each year. The 2004 report covers the years 2000-2004, which became available in 2009.

So, if you want to know about Michigan’s forests, you can obtain a copy of the 210 page report filled with maps, charts, trends, and descriptions. It is U.S. Forest Service “Resource Bulletin NRS-34, Michigan’s Forests 2004”. There are also six-page annual reports of a few key measures.

What does the report tell us? Lots of things, with lots of definitions.

For example, what is the most common tree in Michigan? If you include saplings, then the answer is balsam fir. If you include only trees with a diameter larger than five inches, then the answer is sugar maple, with balsam fir at number eleven.

Which species are most harvested, by volume? Quaking aspen, sugar maple, and then red maple. Which species have the most amount of annual growth? Red maple, sugar maple, and red pine. Which have the highest natural mortality? Quaking aspen, balsam fir, and American elm.

The average diameters have increased since at least 1966 for most major tree species. Michigan has more saw-timber-sized trees than it has had over the last 40-50 years, especially in national forests.

The first portion of the report illustrates many forest descriptors. Forests have many important aspects, such as area, various volumes, size classes, stand composition, age, number of trees, ownership distribution and species statistics. Who is the largest owner of Michigan forest? The State of Michigan.

The second portion of the report addresses the ever-changing aspects of forests. Forests are not static entities. They are constantly changing for many reasons. Ownership patterns have a particular strong influence on forest change. Nearly half the forest in Michigan is owned by private, non-industrial individuals and groups. This ownership experiences a lot of turn-over and that rate is expected to accelerate over the next ten years.

The third portion talks about forest health, including soils, coarse woody debris, carbon stocks, standing dead trees, invasive species and highlights several damaging agents. As you might expect, high profile pests are given special attention, such as emerald ash borer, beech bark disease, gypsy moth and jack pine budworm.

The final portion describes forest product outputs, supporting a 12 billion dollar industry and employing about 150,000 people. Over half the harvest was pulpwood products, with about 40 percent of the total harvest from the northern Lower Peninsula. Most of the Michigan harvest was processed in Michigan. Wisconsin and Indiana are our largest trading partners. Between 2000 and 2004, Michigan lost about 60 wood-using mills, about 19 percent of the 2000 total. Most of these losses were small- and medium-sized sawmills.

Of course, much has changed since 2004 and those recent changes will be reflected in the next five year report. Major mill-closures in the northern Lower Peninsula and the western Upper Peninsula will impact the level of management in regional forests. Without markets, you cannot sell wood. Without removing trees, there isn’t much forest management possible. Without management, fewer benefits from the forest will be realized and forest health is at higher risk. So, according to Michigan State University Extension, a forest inventory provides answers to many fundamental questions. 

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