Leaving an Uncut Tree Facilitates Tree Seedling Diversity in Forest Openings

Research Issue

Forest gap with legacy tree in gap.

Northern hardwood forests aren’t regenerating the way they used to. Changes in soil chemistry and structure from non-native earthworms, proliferation of deer herds and invasive grasses, and shifts in land use and management are reducing both the number and variety of tree seedlings surviving to adulthood.

Researchers with the Northern Research Station and Michigan Technological University experimented with harvesting configurations and resurrected a century-old logging practice to devise a strategy that could preserve the long-term health and diversity of future forests.

Our Research

Conventional harvesting practices in northern hardwood forests often focus on the repeated removal of a particular species (“single-tree selection”). However, the openings in the forest canopy from such treatments have become increasingly insufficient at providing enough sunlight to successfully regenerate sun-loving (“shade-intolerant” and “-midtolerant”) tree species.

Researchers experimented with combining single-tree selection with “group selection” harvesting methods, in which groups of trees were removed to create larger openings in the forest canopy. In 2003, researchers created 49 group selection openings that tested three different size categories: small (about 1/10th of an acre), medium (about 2/10th of an acre), and large (4/10th of an acre).

Scientists also revisited research from the 1920s that explored the effects of “legacy trees” in facilitating the establishment or dominance of a particular species following a timber harvest. The idea of a legacy tree was to log around a single tree, creating an opening with one tree left at its center to serve as a seed source for future propagation. In the current experiment, shade-midtolerant yellow birches (Betula alleghaniensis) were used as legacy trees.

Expected Outcomes

Researchers revisited the test sites 15 years later and found the largest group selection openings also had the greatest number and diversity of regenerated seedlings. Little differed between the smallest gap opening and the control group, which consisted only of single-tree treatments.

Legacy trees were also found to be most successful in propagating themselves within the largest gap size. Research from other studies also suggest legacy trees can benefit most other seedlings at a site by providing a favorable microclimate of cooling shade, reduced wind force, and increased soil moisture.

Research Results

Knapp, Samuel P.; Kern, Christel C.; Webster, Christopher R. 2021. Harvested opening size affects cohort development and failures in a second-growth northern hardwood forest. Forest Ecology and Management. 482: 118804. 10 p. https://doi.org/10.1016/j.foreco.2020.118804.

Knapp, Samuel P.; Webster, Christopher R.; Kern, Christel C. 2019. The Composition and Height of Saplings Capturing Silvicultural Gaps at Two Long-Term Experiments in Managed Northern Hardwood Forests. Forests. 10(10): 855. 23 p. https://doi.org/10.3390/f10100855.

Knapp, Samuel P.; Webster, Christopher R.; Kern, Christel C. 2019. Can group selection with legacy retention change compositional trajectories in conventionally managed hardwoods? Forest Ecology and Management. 448: 174-186. https://doi.org/10.1016/j.foreco.2019.06.005.

Research Participants

Principal Investigator

  • Christel Kern, USDA Forest Service Northern Research Station, Research Forester

Research Partners

  • Samuel Knapp, Michigan Technological University, M.S. Applied Ecology Student
  • Christopher Webster, Michigan Technological University - College of Forest Resources and Environmental Science, Professor
  • Last modified: December 16, 2020