UM Study Finds Effects of Thinning Improve Old-Growth Forest Restoration

By Beacon Staff

Thinning treatments helped restore old-growth forest conditions in a restoration project on the Flathead National Forest, according to a team of researchers from the University of Montana. The study, which was published recently in the Canadian Journal of Forest Research, is being called the most detailed analysis yet of restoration treatment effects on forest spatial patterns.

Andrew Larson, a UM assistant professor of forest ecology and the lead author of the study, said monitoring results from the Meadow Smith old-growth restoration project show thinning treatments successfully restored spatial elements of old-growth forests.

Larson and his co-authors, former UM graduate student Kyle Stover and UM associate research professor Chris Keyes, examined how thinning treatments changed tree patterns in the Southwestern Crown Collaborative (SWCC) project area, a 1.5 million acre area spanning the Blackfoot, Clearwater and Swan river valleys that encompasses portions of the Flathead, Helena and Lolo national forests. In a second analysis, they compared tree maps from restored forests to tree maps from historical old-growth forests to evaluate how effective the treatments were at restoring old-growth conditions.

The U.S. Forest Service identified forest restoration as a top priority in 2009. Following U.S. Secretary of Agriculture Tom Vilsack’s lead, Congress created the Collaborative Forest Landscape Restoration Program (CFLRP).

Vilsack identified restoration as a driving principle of forest management, and the CFLRP provides additional funding for the Forest Service to implement large restoration projects, including the SWCC.

Incorporating spatial heterogeneity into forest restoration treatments has been a longstanding challenge for foresters. Spatial heterogeneity refers to variation in how trees are spaced with respect to each other. Variable tree spacing causes different levels of canopy closure within forests, which regulates important ecological functions.

“While this project successfully restored spatial aspects of old-growth forests, it was largely due to the presence of many live, old ponderosa pine and western larch trees in the project area and their designation for retention in the thinning treatments,” Larson said.

At many sites where restoration is planned, the largest pine and larch trees have been harvested or the pines were killed by beetles. He said restoring spatial heterogeneity at such sites will be much more challenging.

“The clear implication is that foresters will need to directly address spatial patterns in the design and implementation of restoration treatments,” Larson said.

The Meadow Smith project was designed before the Forest Service received funding for SWCC, but it was one of the first forest restoration projects to be implemented in the SWCC project landscape. The monitoring results provide new information for the collaborative and the Forest Service that will help fine-tune future jointly designed restoration projects. Monitoring of understory plants, surface fuels and large down wood is also under way but was not part of the results published July 18.