ESCANABA — All living things die, which is too often perceived as a negative phenomenon. Yet, forest mortality yields an opportunity for both change and rejuvenation. These dynamics are wonderful to witness, and immensely satisfying to initiate and steward.

Foresters, and others, have been regenerating Lake States forests for generations. Monitoring management practices has provided innumerable lessons in how forests respond to disturbances. This acquired knowledge has been folded back into how forests are tended.

The same can be said with recovery following natural disturbances, such as fire, windstorms, ice storms, and insect epidemics. The process of learning by observing, and experimenting, also applies to the more gradual and subtle death of individual trees, which is less dramatic but no less informative.

Forest mortality in the Lake States has reached record levels, exceeding the harvest volume by 17 percent, according to Forest Service inventories. Harvest levels have not gone down but, rather, natural mortality has increased. Our forests are growing older, in general, so increased levels of mortality can be expected.

So, which species account for most of the mortality? Quaking aspen experienced 17 percent of the mortality across the three Lake States. The next top four species are balsam fir (8 percent), green ash (7 percent), paper birch (4 percent), and red maple (4 percent).

Aspen, paper birch, and red maple are short-lived species that have approached the end of their normal lifespan. Green ash has been hit by the exotic emerald ash borer. Balsam fir is another a shorter-lived species but it has also been worked-over by the spruce budworm during the past few years. The other two ashes, white and black, are in the top ten tree species with the highest natural mortality, as is American elm with Dutch elm disease.

Sugar maple is also in the top ten, but not because it is short-lived or has suffered from an insect outbreak. Sugar maple volumes are huge, so even a small percentage loss would spell a large volume compared to other species. Red maple is also a common forest species and its listing among the top ten may be for the same reason, along with its shorter lifespan.

Of course, natural mortality might beg the question about harvested volumes. Which species have the largest harvest volumes in the Lake States? The top five are quaking aspen, sugar maple, red pine, red maple, and red oak. Together, these five species account for sixty percent of the harvest.

Considering both natural mortality and harvest, the forest continues to accrue standing volume. Growth rates still exceed losses. With an idea to the “big picture”, we could be safely harvesting more volume to capture a portion of that which is lost to natural mortality.

Ecologically, dead and dying trees in the forest have much value. Such trees provide a range of microhabitats for many species of wildlife, from nesting and feeding cavities to large woody debris on the ground. Tree decomposition returns minerals and physical structure to forest soils. Decomposer species, such as fungi, are essential to forests.

Carbon is both sequestered and released, sometimes with more being released than sequestered. High mortality ratios may not be the wisest condition in regard to atmospheric carbon and climate change. A younger, more vigorous, forest typically experiences higher sequestration rates than older forests.

However, back to wood volume in a forest inventory, such volume is not necessarily available to the market. Ownership plays a large role. If forestowners do not wish to sell stumpage, then that wood is not on the market. Also, the species mix might not well match the requirements of wood-using mills in a particular area, or at a particular time. Without mill access, then wood cannot be sold. Mill capacity and variety can be increased over time, if a reasonable harvest expectation can be met.

So, if one looks at the natural mortality leaders, quaking aspen, balsam fir, green ash, paper birch, and red maple, how much of that volume might be offered for sale and how much could the current market absorb, before the trees die? This is a good question that does not have a definitive answer.

The supply chain for wood from forestowner to consumer-ready products is complex and variable by geography and time. However, with a “glut” of natural mortality, expanding markets may seem to be a good idea, both economically and environmentally. However, capturing more of that mortality will be a huge challenge.