Cost and efficacy of combining understory resilience treatments with sawlog harvesting operations in the Dry-Belt Douglas-fir

Project Title: Cost and efficacy of combining understory resilience treatments with sawlog harvesting operations in the Dry-Belt Douglas-fir

Recipient: Clinton Community Forest

Region: Cariboo

Theme(s): “Thin it to win it”; “Beyond the sawlog”

Awarded Amount: $50,000

Project period: 2025-2026

Description: Uneven-aged forests of the dry interior contain most of the population and infrastructure throughout the southern interior. These forests are ingrown and subject to uncharacteristically severe fire effects due to the 150 year absence of traditional cultural burning. Cariboo Forest Region has drafted a strategy and best management practices to improve resilience of these forests. The Clinton CF will pilot the application of “Restoration Thinning” from the draft best management practices produced by the Cariboo Forest Region for Dry-Belt Douglas-fir. Planning will include cruising for whole-stand stand and stock tables. The prescription will be implemented in two ways: 1) thinning in the understory is concurrent with overstory thinning; and 2) understory thinning is implemented separately. Shift-level costing will be tracked and submitted to Timber Pricing Branch. Field tours for practitioners and contractors will be offered.

Halfway Reporting:

The following is based on halfway reporting by the grantee.

November 24, 2025

Dry Douglas-fir forests in South Cariboo have it hard. Growing season frost, heat injury, drought, bark beetles and spruce budworm contribute to a hard life. Forests were historically quite open under the influence of the cultural use of fire. But currently, stands are generally made up of a low volume overstory and a very high-density understory. Where unsalvaged patches of lodgepole pine have been killed by pine bark beetles, they are now on the ground as an elevated fuel bed. Without intervention, these forests will burn with high intensity and high levels of mortality.

Under this project the Clinton Community Forest and its contractors are working to combine overstory and understory thinning, to improve:

• the resilience of stands to wildfire;
• the growth of understory trees; and
• the resistance of trees and stands to spruce budworm and Douglas-fir bark beetles.

We think our best opportunity is to treat the understory in combination with commercial logging, or a combination of modified logging practices combined with mulching to reduce understory density, and we have tested several methods to look for the best outcomes at least costs. Most of our effort has been focused on using the feller buncher to reduce the understory density and add the small trees to the commercial logs for skidding to the landing where they can be ground up for hog fuel, along with the tops and branches of the commercial logs. We have also used two different mulching machines after logging, felling much of the understory and breaking it up to be left on the ground.

The Clinton Community Forest public field tour visited the site in September during operations, and the visitors reacted favorably to the results of the work. Partial-cut harvesting that removes only a portion of the stand is always appreciated. The reduction of the understory opens the stand up and gives us hope that the residual stands will be much more productive. It was interesting for the public to be able to see the specialized equipment used for mulching.

We have measured the stands before logging, and we will remeasure after logging so that we can understand the impacts of our work on stand volume, understory density and surface fuel loading. We have been keeping detailed cost and harvest volume records, so that we can report confidently on the cost per hectare and the cost per cubic metre of logs and hog fuel in this project.

We appreciate financial support for this project from SIP, 100 Mile House Forest District and the Forest Enhancement Society of BC. We also value the collaboration of the Cariboo Natural Resource Region and the Tree Ring Lab at UBC Forestry. We particularly appreciate the contractors and the workers who have contributed their skills, knowledge and equipment to this project.

Photo: Untreated stands have an open overstory over a very dense understory with chronic spruce budworm defoliation and a lot of ladder fuels. Credit: K. Day

Photo: Block 7 untreated (left) and treated (right) after logging and mulching understory.. Credit: K. Day

Photo: Public field tour visited the various treatment combinations on Sep 27, 2025. Credit: S. Law

Photo: Block 3 was bunched and understory thinned at the same time, with biomass piled with sawlogs for skidding. Credit: S. Law

Photo: Block 3 buncher operator Lance Bob cutting understory and sawlogs at the same time. Credit: K. Day