Large-Tree Retention

Section 102(f) governs vegetation treatments in covered projects outside of old growth, and where the resource management plan does not contain old-growth management direction. The section requires such treatments to be carried out in a manner that:

• Will “modify fire behavior, as measured by the projected reduction of uncharacteristically severe wildland fire effects for the forest type (such as adverse soil impacts, tree mortality, or other impacts).” In achieving this objective, vegetation treatments are to focus “largely” on small-diameter trees, thinning, strategic fuel breaks, and prescribed fire (figures 14 and 15).

Figure 14—After decades of wildland fire exclusion, some ecosystems, such as
this ponderosa pine forest in southern Oregon, have become over­grown and
unhealthy, leaving them unsuitable for wildlife and hazardous to communities nearby.

Figure 15—Ecosystem health has been restored and the risk of high-intensity
wildland fire has been reduced after mechanical treatments, followed by
low-intensity burning, in the ponderosa pine forest shown above.

• Maximize “the retention of large trees, as appropriate for the forest type, to the extent that the large trees promote fire-resilient stands.”

The HFRA also states that the large-tree retention requirements of Section 102(f) must not prevent agencies from reducing wildland fire risk to communities, municipal water supplies, and at-risk Federal land.

In areas where large-tree retention requirements apply, resource managers should design projects that retain large trees to the extent possible, while they also:

• Are appropriate for the forest type
  
  
• Will reduce uncharacteristically severe wildland fire effects within the treated area
  
  
• Will meet the objective of reducing wildland fire risk to communities, municipal water supplies, and at-risk Federal land

Specific vegetation treatment methods to be applied within these areas should be guided by the key objectives described above.

Silviculture prescriptions should be designed for forest vegetation treatments that integrate fuel and other resource objectives to meet the resource management plan direction. The silviculture prescription should prescribe for retention of large, fire-resilient trees (generally intolerant tree species adapted to fire processes) and retain large trees to the degree this practice is consistent with the objective of maintaining or restoring fire-resilient stands. However, large trees of selected species that are not adapted to fire processes may need to be removed to promote greater fire resiliency. Similarly, the removal of small- to mid-sized trees will generally be needed to reduce fuel ladders within the treatment area, curtailing uncharacteristically severe wildland fire effects and enabling use of prescribed fire. Trees in a variety of size classes may need to be removed in these areas to reduce wildland fire risk to communities, municipal water supplies, and at-risk Federal land. These practices are allowed under the HFRA.

In determining characteristic large-tree sizes appropriate for the forest type, resource managers may explore using the ecological definition of old growth developed for the forest type as one means of identifying diameter ranges for the tree species covered by the definition. USDA Forest Service ecological definitions for forest types are listed in the References section.

Resource managers should consider using growth models and other simulation tools when developing treatment strategies for areas where large-tree retention provisions apply. Models, such as the Forest Vegetation Simulator coupled with the Fire and Fuels Extension (see References, Old-Growth and Large-Tree Retention, Project-Level Guidance), allow treatment scenarios to be analyzed through time to determine their effects on fire behavior at the stand level and to help predict fire effects. Through using this kind of model, practitioners can determine the optimal treatment or set of treatments within a particular forest type that will help achieve the objective of retaining large trees, to the extent that is consistent with the objective of promoting fire-resilient stands.