Glenn Ahrens, OSU Forestry and Natural Resources Extension Agent – Clackamas, Marion, and Hood River Counties
At Hopkins Demonstration Forest we have an area of maturing forest – 80 or more years old – that we would like to manage with continued thinning or selective cutting rather than clearcutting. As I discussed in Part 1 of this story, this is a common situation for family forest owners. Many are interested in periodic selective harvesting of trees or small patches and keeping options open for the future. There are many challenges and tradeoffs to consider, but now we have to choose an option for our Hillside Forest stand at Hopkins.
Like many woodland owners, we have to balance the need for revenue with our other goals for aesthetics, recreation, and wildlife. In our case, goals for education and demonstration are also a high priority. This year in particular, we have major financial challenges to sustaining our woodland enterprise due to the COVID-19 pandemic. We have accumulated valuable timber inventory over the years since we don’t cut all of our annual growth. So, we are considering how much to draw upon our timber account to get us through hard times. And what kind of silvicultural options do we want to demonstrate in the process?
Forest Stand Conditions – The forest stands in question are two units of similar size, collectively called the Hillside Forest, occupying about 25 acres on the slope from hilltop (700 foot elevation) to stream bottom (400 foot elevation). The stands are composed of second-growth western redcedar and Douglas-fir regenerated after logging in the late 1930’s. The stands have been thinned three times over the last 30 years, maintaining many well-spaced trees with good crowns. They should be relatively stable when they are retained after thinning. There are also clumps of intermediate canopy trees and scattered gaps with brush and bigleaf maples. Current stand density is approaching the upper end of the “optimal management zone” based on average DBH (22 inches) and trees per acre (100). Read more about competition levels and on this approach to density management here.
The forest type changes from a drier Douglas-fir/cedar stand on the upper slope to a more moist cedar dominated stand on the lower slope. While cedar grows a little slower than Douglas-fir, it is now a major co-dominant component of our forest because of the residual cedar left after logging in the 1930’s (many of the cedars are over 100 years old now). Shade tolerant cedar provides the opportunity to manage for regeneration and multiple aged cohorts with thinning and smaller gaps, while Douglas-fir requires larger openings for good regeneration.
Goals and Objectives – Hopkins is managed to provide an “accessible example of sustainable forestry” and to support “science-based education to enhance understanding of, and appreciation for the complexities and benefits of woodland management.” It is a working forest managed for multiple objectives including:
- hands-on woodlands education for diverse audiences,
- timber resources and revenue from timber harvests to help support the organization,
- wildlife and fish habitat to accommodate a diverse natural fauna,
- soil and water resources to maintain or enhance soil productivity and water quality,
- and recreation opportunities, in conjunction with project development and educational activities.
For the Hillside Forest stands, we are focused on demonstrating the “complexities and benefits” of trying to meet all objectives in one stand with thinning and selective management of a mature forest. On the majority of the Hillside Forest, we are planning a relatively light thinning, removing about 25% of the trees and a similar portion of the standing volume, to reduce stand density to the lower end of the “optimal density management zone”. Such that the trees we leave should be able to refill the growing space. While we are at it, extra work to clear some of the brushy gaps and provide new regeneration of cedar is also planned. In one area of about 5 acres, where trees are widely spaced and there are more brush-filled gaps, we will cut most trees and regenerate a mix of Douglas-fir and cedar. The target for timber volume removal is about 4,000-5,000 board feet per acre in thinned areas and 15,000-20,000 board feet per acre in the larger clearing.
A key question for the longer-term is how long to continue thinning the large overstory trees and whether or not to do more regeneration harvesting to start new stands of Douglas-fir. Theoretically, we could just keep thinning the overstory and grow the stand from the current 22 inch average diameter to 30 inches (~30-35 years out) or 40 inches (~70-80 years out), at which point about 30 to 35 trees per acre would fully occupy the site. Another option is to convert some areas to uneven-aged management, with individual tree selection to regenerate cedar, along with larger patches (>3 acres) of regeneration harvest to provide new cohorts of Douglas-fir. For now, the plan for most of the Hillside Forest is to maintain individual tree crown vigor with thinning and keep options open for continued thinning or uneven-aged management in the future.
Tradeoffs and Costs – Felling and yarding tall timber (100-140 feet tall) while protecting residual trees requires careful and skillful operations. That and the relatively low volume removed per acre will increase logging costs compared to clearcutting. But the larger, older Douglas-fir and especially the cedar have potential to be higher value. In terms of timber value, cedar logs are even more valuable than Douglas-fir ($1,000-1,500/mbf vs. $500-800/mbf delivered log prices over the last ten years). We also hope to produce higher value Douglas-fir sawlogs and transmission poles with this mature-forest management system.
While the planned thinning is relatively light, there is still a risk of loss or damage to residual trees from sudden exposure to sun and wind. The cedar may be particularly vulnerable to sun and heat exposure, which seems to be an increasing challenge for cedar at low-elevations in the Willamette Valley margins. There is also the potential for damage to soils, roots, stems, and crowns during thinning, especially with the large size of some trees being felled and yarded.
Educational opportunity – In keeping with our objective for hands-on woodland education and “learning while doing”, we would like to involve people in preparation and execution of the thinning project. Tasks include meeting with foresters, log buyers, and loggers to develop the operational plan for access, skid trails, and tree selection. We need help conducting pre-harvest inventory, marking stand boundaries, and selecting and marking which trees to leave or cut to meet our thinning target. Given the challenges of in-person events during the COVID-19 pandemic, we anticipate limited opportunities for a few people at a time in the woods. We also would like to capture some of the work on video to share with others online. If you are interested in participating, please contact me at email@example.com. To follow our progress, stay tuned for the next installment of this story.
We are pursuing this more challenging and costly style of management to see if we can “have it all” in one beautiful 25-acre hillside forest – timber revenue, species diversity, mature forest habitat, recreation value, and public education. Whatever happens, we will learn from the process.