Data shows that Michigan harvests a lot of wood but grows even more

Collecting data on Michigan's wood growth and harvest is important as the state's forests are worth billions as well as value in environmental terms.

Michigan harvests a lot of wood. We see the trucks moving every day. But, Michigan also grows a lot of wood.

What is the balance?

On a statewide basis, Michigan grows a bit more than twice the volume that it harvests -- a ratio of about 2-to-1. Michigan’s growth-to-harvest figure is higher than that of either Wisconsin or Minnesota. Across the nation, it ranks in the middle of the pack.

A ratio greater than 1-to-0 means more wood grows than is harvested. The higher the number, the larger the proportion of growth there is. That could mean either the growth is aggressive or harvest levels are low. A ratio less than 1-to-0 could mean either natural mortality is high or harvest levels are high.

Each year, more and more wood accumulates in Michigan forests. Some would say this is a good thing. Others see a portion of the growth as a sustainable way to bolster a part of Michigan’s economy, especially in rural areas.

Keep in mind that forest statistics are constantly moving targets. More importantly, they vary across different regions within Michigan. The 2-1 ratio is not uniform across the state and also varies among tree species.

It’s also important to understand that wood that accumulates in the inventory does not mean it is available for harvesting. Inventory and availability are two different concepts. An owner won’t necessarily sell timber just because it’s there. And, nearly half of Michigan’s forest is owned by families and individuals.

By looking closer at the inventory data, meaningful highlights can be discovered. This is especially important information for investors and planners looking at establishing a new forest products company or biomass energy facility.

For instance, the growth-to-harvest ratio increases from 1-to-3 in the Upper Peninsula, to nearly 4-to-0 in the Southern Lower Peninsula. In the Northern Lower Peninsula, there is more growth accumulation on the east side than on the west side.

By tree species, the ratio varies even more widely.

All of our common tree species are growing at rates higher than harvest. White pine grows nearly nine times the volume of its annual harvest. The five most common species in Michigan -- sugar maple, red maple, cedar, red pine, and quaking aspen -- are growing at rates of 1-9, 2-5, 4-6, 2-6, and 1-4, respectively.

Other tree species are not doing as well, mostly because of impacts by exotic pests or natural cycles leading to maturity. Where possible, harvest levels increase for these species, while the still wood remains sound. Some of the declining species include the elms, paper birch, jack pine, beech, and white ash.

How do forest scientists know these sorts of things?

Since the 1930s, the U.S. Congress has charged and funded the U.S. Forest Service to collect forest inventory across the United States, on all ownerships. These inventories are done through a special unit called the Forest Inventory and Analysis (FIA) program. This unit is often cited as the source for all sorts of descriptive data, often referred to as FIA data, for forests.

The FIA unit counts trees. Many pieces of information about the site and sample trees are collected. There are more than 10,000 forested plots across the state and dozens of measured items. Each year, a fifth of the plots are remeasured in the field and the rest are modeled. Every five years, a report is issued that describes our forests.

It’s an expensive endeavor. However, our forests are worth billions in monetary terms, alone. Additionally, there are values for environmental services and sense of place that are difficult to assign a dollar value. Nevertheless, we do, indeed, have a pretty good idea about the status of our forests.

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