Different forest ecosystems in Michigan are initiated and/or maintained by different ecological disturbances.

A disturbance is anything that regulates the amount of living biomass.

Fire is an ecological disturbance that has shaped plant communities for thousands of years. Within the complexity of a burned forest are found habitats for other living organisms.

While springtime often heralds understandable concerns about wildfire because of human activity and the combination of low humidity, dry plant materials, and strong winds, fire is nonetheless important to biodiversity.

For instance, an assessment of forests and other ecosystems adapted to fire in the upper Great Lakes suggested that some regions may have 21 species of mammals, birds, and herpetofauna (reptiles and amphibians) considered “fire dependent” (“The Wildlife Professional,” 2015, v.9, pages 52-plus).

Suppression of fire, therefore, has impacts on many wildlife species, not only the Kirtland’s warbler.

Like forest and wildlife ecology, fire ecology has its own vocabulary.

Ground fires burn below the ground, often in organic soils, and can be difficult to manage. The 1976 Seney Fire was primarily a ground fire and it took a winter to finally extinguish.

Surface fires, conversely, burn on the forest floor and are usually the type of fire planned in prescribed (or controlled) fires.

Crown fires are those that burn to the tops of trees. Crown fires are usually aided by wind and a layering of forest vegetation that provides a “ladder” of fuels. The recent Blue Lakes Fire was a crown fire.

The impact of fire on vegetation is referred to as fire severity and the amount of energy released by a fire is called fire intensity.

Crown fires tend to be high severity and high intensity.

The time it takes a fire to burn the same location is called the fire return interval, while the time it takes to burn an entire area of interest is called the fire rotation or fire cycle. Fire return intervals for many pine ecosystems in Michigan ranged from 35 to 65 years, historically.

By studying tree rings obtained from cores of live and dead trees, research in upper Michigan showed how a natural fire regime before European settlement initiated and maintained forests dominated by red pine.

Over 400 years, the fire regime was dominated by surface fires that maintained two to three age classes of trees and scattered snags and downed wood. Perhaps the most interesting finding was that larger fires generally occurred during the late summer, when lightning strikes were common, not the spring (“Canadian Journal Forest Research,” 2008, v.38, pages 2,497-plus).

Some of the forests in the study area were altered in the early 20th century, first by logging, then by fires fed by logging slash, and then by fire suppression.

A follow-up study showed how those “altered” forests had a different bird community than “benchmark” forests that had not been logged and still had an intact fire regime. Benchmark forests had more neotropical, migratory bird species, while altered forests more resident species (“Forest Ecology and Management,” 2014, v.318, pages 183-plus).

Studies such as those can provide an evidence-based approach to fire, forest, and biodiversity management.

For instance, results showed how forests dominated by multiple age classes of red pine were not initiated by stand-replacing crown fire, but through repeated surface fires. That contrasts with how we traditionally manage red pine plantations with clearcuts and the replanting of one age class. Research also provided guideposts for deadwood management.

Study findings also illustrated the need for shifting more prescribed fire to the late summer. Burning in the spring has been the traditional approach, but little impact occurs to live vegetation because many plants are dormant.

If, for instance, one wants to reduce the amount of encroachment of red maple in a natural pine area, prescribed surface fire in the late summer is likely to have more impact as the heat impacts the thin-barked red maple, not the thick-barked red pine.

As we try to safely get through a spring fire season, we all should keep in mind the important role fire plays in some of our native ecosystems and encourage the wise use of more prescribed fire.

Greg Corace is the forest and wildlife ecologist for the Alpena-Montmorency Conservation District. For more information, including assistance with the Qualified Forest Program and related forest planning and management, email Corace at greg.corace@macd.org.