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Fall 2020
Nature Notes is the Minnesota Scientific and Natural Areas quarterly newsletter. Here's what's in store this issue!
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The Rare and Wild: Old Growth Forests of Minnesota
Learn more about one of the rare native plant communities that Scientific and Natural Areas protect in this 2020 series about the “Rare and Wild” in Minnesota!
AmberBeth VanNingen, SNA Northeast Regional Specialist
Old growth forests are evocative. They bring to mind towering trees and shadowy, ancient places. Entering one can feel like a gateway to a different world. Old growth forests can also surprise, looking nothing like what we expect.
What are they?
Old growth forests have canopies dominated by large trees from 120 to over 300 years old. In Minnesota, these canopies can be made up of sugar maple, ashes, red and white pine, white cedar, oaks, tamarack, and spruces. But old growth forests are more than just old, big trees. They contain trees of all sizes and ages including shade-tolerant species like ironwood, Canada yew, pagoda dogwood, and sugar maple and white cedar seedlings in the understory ready to break through and join the canopy when given the opportunity. The old trees themselves aren’t always that big. Old growth black ash swamps can be quite deceptive. The trees may only be 9-11” across, but can be over 120 years old! Regardless of the size of the old trees, old growth forests take time to develop and have generally been spared catastrophic disturbances that may replace the entire stand, such as major fires and windstorms, and human intervention such as roads, development, and logging. Evidence of this is seen in the large amounts of snags and fallen dead wood, including some of the largest trees as they are felled by wind, ice, and fire over time.
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Sugar maple seedlings carpet the forest floor at Lutsen SNA. Photo by John Gregor, © ColdSnap.
The DNR has a formal internal process for recognizing and designating old growth stands on its land. Much of this work was done in the 1990s for upland and lowland hardwood forests. To qualify, the stands have to be at least 120 years old, 20 acres in size, contain other old growth characteristics (e.g., snags), and have experienced little human disturbance. Potential sites were field checked and evaluations completed. In some areas of the state, future old growth forests (those less than 120 years, but with other old growth characteristics) were designated to ensure a diversity of old forest on the landscape. A process to designate lowland conifer old growth (white cedar, tamarack, and black spruce) is currently underway and the DNR will be publishing proposed designations for public review in the near future.
Where are they in Minnesota?
Old growth forests can be found almost anywhere there are forests in Minnesota, from the vast peatlands in the northcentral part of the state (such as Norris Camp Peatland SNA) to the cool shade of Townsend Woods in the Big Woods, to the sugar maple forests of Spring Beauty Northern Hardwoods SNA on the North Shore and many forests in between. Some of the best places to access old growth forests are state parks and SNAs, although they occur on just about every kind of state land and on other ownerships, such as in the Boundary Waters Canoe Area Wilderness and Nature Conservancy preserves. The DNR old growth website has a good list of places to visit on state lands.
Why are they important?
It is thought that about 51% of Minnesota’s forests were in old growth stages prior to European settlement in the late 1800s to early 1900s. Only about 4% of Minnesota's forested land remains old growth today. Their rarity is part of their importance. Old growth forests also provide important habitat for an abundance of species, from those shade tolerant shrubs (who also tend to not tolerate a lot of disturbance), to animals such as fisher, pine marten, and porcupines that need big old trees as dens for their young. Woodpeckers of all stripes flock to old growth, as the old trees and snags host a diversity of insects. Old growth provides a benchmark for us when restoring or managing younger forests as well.
Old trees are also important as long-standing witnesses and survivors. Kelly Applegate, Director of Resource Management for the Mille Lacs Band of Ojibwe, tells of a consultation with Elders on the possible removal of old trees at a building site. The Elders responded by asking, “Would you cut me down because I’m not young and fresh? Am I disposable?” For the answer to those questions, you can still see these old trees in front of the Band’s government building. Those trees are important.
Who works on them?
The teams within the DNR that work on old growth designation and management are interdisciplinary, with foresters, ecologists, wildlife and nongame biologists, and recreation staff represented. Old growth management focuses on maintaining or enhancing the old growth characteristics for which it was designated and providing for recreation where appropriate. While it is true old growth is rarely actively managed, several tools such as prescribed fires and invasive species treatment are available to land managers. Itasca State Park is one place you can visit to see prescribed fire used in old pine and other forest types to encourage pine regeneration and manage fuel loads. Itasca Wilderness Sanctuary SNA, nested within the park, contains over 800 acres of designated old growth and has been included in this project.
Other types of management, such as timber harvesting is not allowed. This includes salvage sales after disturbances. Wildlife openings and browse regeneration development do not occur and pesticides cannot be used (except to protect against serious invasive species threats). No development such as new roads and trails can be made as well.
While old growth forests may seem eternal, they are just part of the forest cycle of life. The old trees will eventually die, blow over, or be burned in a fire and end up on the forest floor. The understory will change as opportunistic plants grow in the newly created gaps in the canopy. Animals that use forest gaps and younger forests will move in and the old growth forests of today will transition into the younger forests of tomorrow. Similarly, the young and middle-aged forests of today, if undisturbed, will grow into the old growth forests of tomorrow and the cycle will continue.
A large, old white pine was felled by a wind storm at Lost 40 SNA in 2018. Photo by AmberBeth VanNingen, MN DNR.
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