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Forest restoration in light of oak decline

Ecologically sustainable forest management requires consideration of how forests once looked and how they once functioned.

That information provides a management framework for forests as complex ecosystems.

Complexity, within natural limits described in the scientific literature for each forest type, provides greater potential for adapting to future uncertainties such as climate change (see Forest Ecology and Management v. 421, p. 59-plus).

Forest restoration is the process of reintroducing aspects of a forest that have been lost, usually because of human activity. To be evidence-based, forest restoration requires quantifiable information on how forests once looked and how they once functioned.

For instance, in eastern upper Michigan, published studies described how surface fires on an approximately 50- to 60-year return interval promoted and maintained forests of red and eastern white pine. Those fires did not kill larger trees with thicker bark, but did kill smaller trees with thinner bark. Fires also prepared the forest floor for seedling establishment.

Studies also provided information on the range of tree size classes and the amount of deadwood in these forests. To provide a wildlife perspective, a study then compared the bird communities of the restoration benchmarks and the altered forests that underwent restoration treatments. Finally, the effectiveness of those forest restoration treatments was determined (see references in Forest Ecosystems 2020 v. 7, pg. 1-plus).

In a similar manner, understanding what forests in northeastern lower Michigan once looked like and how they once worked can provide guidance to management in light of oak decline (see previous articles). Since many of our forests are in an altered ecological state, one can view oak decline as an opportunity for restoring lost forest characteristics.

As an example, oak wilt is a fungal pathogen killing northern red oaks and black oaks. The fungus moves from tree to tree through roots and by insects, with root movement being the more efficient. While there are some intensive and costly management techniques that slow the spread of oak with variable levels of effectiveness, an alternative strategy is to view oak wilt as a symptom of the broader issue of forests in poor ecological condition.

Oak-dominated forests can be severely impacted by oak wilt. If forests have more tree species diversity (like they once did) and more evenness in abundance among species, the impacts of oak wilt would be less.

Instead of trying to manage for an altered state of oak dominance, view oak wilt from an ecological perspective. In other words, understand and appreciate what oak mortality is doing to the broader forest. For example, take advantage of canopy gaps created by tree mortality and restore missing or less common tree species by hand planting seedlings. On drier (xeric) soils, plant red pine, jack pine, and/or eastern white pine. On more moist (mesic) soils, plant white spruce and eastern white pine. Native deciduous tree species can be planted, too, but those will likely require protection from browsers.

The canopy gaps will provide the necessary sunlight for seedlings to flourish, especially if a quarter-acre or larger. And the dead and dying oak trees will provide conditions for numerous other species over time before providing nutrients back into the forest soils.

In a similar manner for oak-dominated stands that do not yet have oak wilt or show oak decline, mitigate for the potential for oak wilt by harvesting many (not all!) northern red oak and black oak, while leaving the white oak and standing dead (snags). The forest after treatment should still retain all tree species before treatment, but retained trees are spaced more than 100 feet apart. Canopy gaps can be planted with seedlings as mentioned above.

Traditional forest management techniques were devised to produce forest products. Newer forest management approaches have been developed to meet other ownership goals, including biodiversity maintenance, wildlife habitat management, and climate change adaptation. Those approaches can also be used to mitigate for the effects of forest stressors, such as oak wilt, if viewed from a restoration perspective.

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

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