Despite the interest in heterogeneous fuel and fire treatments in California (See GTRs 220 and 237), there are few on-the-ground examples of finished treatments for managers to visit and learn from. On August 24th, 2012 Erick Knapp (USFS PSW) and Maria Benech (USFS Stanislaus NF) led a CFSC-organized field trip to the Stanislaus-Tuolumne Experimental Forest (STEF), where their crews have finished thinning treatments on one of the largest variable-density thinning projects currently underway in the state. The different treatments (variable thin-no burn, variable thin-burn, control) are part of a study intended to investigate the ecological effects of structural variability through forest thinning and burning operations.
One of the main goals of the project is to try to recreate a similar variable stand structure to what was found in the central Sierras prior to fire suppression and logging. In 1929 an inventory was taken of the same STEF lands for a “methods of cutting study”. Then, much of the forest area exhibited distinct gaps and patches of trees - separate groups of trees each with similar density, basal area, and canopy cover, along with gaps of understory vegetation with little to no trees mixed in to the overall stand.
The August field trip visited four different areas within the experimental forest. At each stop the group walked through different treatments and controls to discuss topics ranging from operational considerations to wildlife habitat. The variability within each treatment was obvious – there would be open patches with one to three large trees and snags next to dense groups of small firs and cedars. The thinned stands also provided a stark contrast to the untreated control stands, which were generally were dense with shade-tolerant understory trees and ladder fuels throughout, in addition to the larger legacy trees common throughout the STEF.
The high-variability treatment prescription evolved over 3 years after much discussion and planning with staff and stakeholders. Working with all the marking crews at once to mark sample treatments, before each crew went off to work individually, helped create a shared baseline of how to mark the treatments. Additionally, the marking crews included an assemblage of wildlife biologists, botanists, fuels specialists, silviculturalists, and planners. Most of the treatments used a leave-tree marking guideline, while cut-tree guidelines were used in some of the old-growth stands.
Knapp and Benech emphasized that the marking guidelines are flexible – “this means few black and white decisions and no right or wrong answers, which was initially frustrating for some.” Often, certain stand characteristics such as remnant black oaks, root disease pockets, or legacy trees would be used as “anchors” to plan around. This fluid approach draws a contrast to the standardized thin-from-below treatments commonly used in traditional thinning projects. While more time-consuming at first, as the crews become more experienced at marking these complex treatments the rate of marking progress grew closer to the rate for more traditional treatments.
Creating suitable wildlife habitat and refugia was a factor that helped guide the creation of patch and gap sizes and distributions. This was evident during the field tour: treated stands showed a variety of large-diameter and course woody debris on the forest floor as well as a spectrum of different tree sizes and crown densities. As such the treatments were designed to provide cover and habitat to a wide range of wildlife, and to avoid single-species management practices. The concept of this design is “not to manage every slice of pie for every species,” said Eric Knapp during the tour.
Outreach to stakeholders was key to successfully implementing these treatments, particularly in regard to the lack of diameter limits on tree removal in the experimental forest. Throughout the planning process, meetings and field visits were held with stakeholders to help build trust and accountability. Showing a comparison of current density, tree arrangement, and understory vegetation to the 1929 stem maps of the forest helped to visualize and contextualize planned treatments.
Prescribed burns of some of the treated stands at the STEF are scheduled for this fall. Hopefully we’ll be able to plan another field visit afterwards or in the spring, so stay tuned.