Importance of old-growth forests

"The provision for true old growth should be regarded as an essential activity of forestry, just as the provision for wood, wildlife, recreation, and water."
Minnesota Society of American Foresters, Old-growth Task Force (May 1992)

Old-growth forests are a unique, nearly vanished piece of Minnesota's history and ecology. They are the remnants of the plant life that once covered 51% of the state's forested regions, and their harvest delivered immense wealth to individuals and the government, speeding the development of the state's early economy.

Today, ecologically significant old-growth forests are protected from harvest and represent new valves in modern forest management. Old-growth forests can be compared to similar but harvested forests, and conclusions can be reached about the effect of harvest on soils, plant and animal life, the rate of tree growth, and many other parts of a forest's ecology. This kind of research can help improve forest management approaches aimed at supplying wood reliably to the economy while guaranteeing a healthy ecosystem for future harvest and enjoyment.

Old-growth white pine and red pine forest near Grand Rapids, Minnesota, <em>circa</em> 1900.
Old-growth white pine and red pine forest near Grand Rapids, Minnesota, circa 1900.

Old-growth trees harvested and ready for market, circa 1900.
Old-growth trees harvested and ready for market, circa 1900.

Modern white pine harvesting.
Modern white pine harvesting.

A second value of old-growth forests to modern forest management is to recreate in scattered locations the conditions found in Minnesota's forests of the 1850's, before large-scale commercial logging began. Old-growth forests provide unique habitat, sheltering species which do better in old forests than young, and serving as genetic reservoirs--just some of the benefits researchers have discovered.

Unique habitat

  • Snags provide nesting, foraging, and denning sites for more than 40 species of forest birds and mammals.
  • Fallen tree trunks and large branches provide shelter and foraging grounds for salamanders, small mammals, and arthropods (e.g., beetles, spiders).
  • Old pine trees provide nesting sites for bald eagles and ospreys, and escape routes for young bear.

Species benefits

  • More kinds of lichen and fungi species live in old-growth forests than younger ones.
  • A larger amount of nitrogen-fixing lichens--organisms providing critical nutrients--is found in old-growth forests than younger ones.
  • Many beetles live in old-growth than other forest types.
  • Dragonflies are more common and in greater variety where streams and lakes are next to old-growth forests.
  • Woodpeckers and 39 species of songbirds are more frequent in older forests than younger.
  • Several kinds of hawks and owls prefer older forests.

Genetic reservoirs

Supercanopy red pine towers over its neighbors.
Supercanopy red pine towers over its neighbors. (photo by Jon Rosales)

We are just beginning to understand the full implications of preserving genetic diversity. But what is understood points toward the importance of genetic diversity for forest health, forest research, and forest restoration and conservation.

  • The tallest, straightest trees in Minnesota's forests were cut between 1850 and 1920, and often their offspring were destroyed by fire, plowing, or subsequent timber cutting. We do not know whether the forest's remaining trees have the same genes as those that disappeared, but some researchers suspect they do not. Dr. Lee Frelich at the University of Minnesota who studies old trees in areas that were never clear-cut, suspects that the old trees are genetically predisposed to grow taller than trees in surrounding heavily cut landscapes that are often established from seed from trees by-passed by loggers. This theory can be tested by comparing remaining old-growth stands to those managed using traditional forestry and timber practices.
  • Old-growth forests can thus serve a source of biological restoration. Thousands of years of genetic heritage are embodied in these stands. Having survived under changing conditions, old-growth trees may contain genes that will enable them to survive global climate change, new diseases, and the uncertainties of the future better than their neighbors. These stands could be invaluable for the restoration fo commercial forests, agricultural lands, and urban forests.