Treatment zones – This PM tracks fuels reduction treatments in four treatment zones, defined below.

• Built Environment – The built environment contains the areas of highest density of residences, commercial structures and critical infrastructure in the Basin. Publicly owned parcels in the urban core that are undeveloped receive fuels reduction treatment.
• Community defense zone – A strip that is generally ¼ mile wide (and sometimes wider) that surrounds the urban core and is in close proximity to communities. This zone represents the Community Wildfire Protection Wild-Urban Interface (WUI).
• Threat zone – A buffer extending from ¼ mile to 1.5 miles beyond the urban core, beyond the community defense zone. This zone allows for a greater capability of fire suppression, firefighter safety and community protection. The threat zone and the community defense zone together are known as the USFS WUI.
• General forest – All areas of the basin that are beyond the threat zone. The majority of the general forest is under USFS ownership. Generally, treatments here are strategically located to reduce fire potential on a landscape scale.

Treatment types – An area is considered treated if one of the following actions is performed:

• Chipping – Used to reduce ladder and surface fuels. Chippers are used to create chips of material that can either be removed from the site as biomass or spread across the ground.
• Hand thinning – Reduces the number of trees, which reduces potential for crown fire. Ground-based thinning is generally used for trees with diameter at breast height of less than 16 inches, on steeper slopes and in sensitive areas
• Mastication – Used to reduce ladder and surface fuels. Masticators grind up material into irregular-sized chunks which are left on-site.
• Mechanical thinning – Reduces the number of trees, which reduces potential for crown fire. Mechanical thinning is generally used for removal of larger trees. Ground-based mechanical thinning is used in areas that are sensitive or have slopes of less than 30 percent. Aerial-based mechanical thinning is used to remove trees from steeper slopes.
• Prescribed burning – Reduces fuels by burning them on-site and restores fire as an essential element within the fire-adapted ecosystem. Pile burning is used primarily in a suite of initial treatments as a means of reducing fuels that have been hand- or machine-piled and where removal is not feasible. Underburning is used generally as a maintenance treatment to reduce fuels and restore fire to the ecosystem. Typically, prescribed burning results in mortality of individual or small clumps of trees that provide wildlife habitat.
• Pruning – Removes lower branches from trees to increase crown-base height. Generally only used for small areas.
• Biomass removal – Material removed from treatment area to be utilized in the form of chip, mulch, small or large logs. This material may provide some revenue to reduce the net cost of fuels reduction projects

The Acres of Forest Fuels Reduction Treatment Performance Measure measures the number of acres of fuels reduction treatments performed in the general forest and the community defense zone (wild-urban interface). For accomplishments related to defensible space around structures in the urban core, refer to the Parcels Treated for Defensible Space Performance Measure.