The NFPA recommends creating defensible space by maintaining specific tree spacing and pruning to reduce wildfire risk. Key guidelines include pruning lower branches at least six to ten feet from the ground, ensuring at least ten feet of separation between tree canopies and structures, and maintaining horizontal spacing of at least 18 feet between mature tree crowns, increasing on slopes
Defensible space is the buffer between your structure and the surrounding area. Adequate defensible space acts as a barrier to slow or halt the progress of fire that would otherwise engulf your property. It also helps ensure the safety of firefighters defending your home.
Pruning Guidelines
To prune a tree, first identify and remove the “three Ds”—dead, diseased, or damaged branches—using sharp tools. Then, use heading cuts to shorten branches by cutting above an outward-facing bud or a side branch, or thinning cuts to remove branches entirely at their origin, leaving the branch collar intact. Make cuts for larger branches using the three-cut method to prevent bark tearing. Prune when the tree is dormant in late fall or winter to maximize energy reserves, and never remove more than 25% of a young tree’s canopy or 10% of an older tree’s canopy in one year.
- Clear “Ladder Fuels”: Remove all dead vegetation, tall grasses, shrubs, and tree branches from the ground up to 6-10 feet high to prevent fires from climbing from the ground into the tree canopy.
- Structure Clearance: Prune all tree branches that overhang roofs, chimneys, or other structures.
- Objective-Based Pruning: Ensure you have a clear objective before pruning, such as removing dead or diseased limbs or improving tree health.
Tree Spacing Guidelines
- Defensible Space Zones:
- Zone 1 (0-30 feet): Thin out trees and shrubs and maintain low, well-watered, and less flammable vegetation.
- Zone 3 (30-100 feet): Create fuel breaks with non-combustible or low-fire-risk ground covers and ensure canopies are spaced appropriately.
- Horizontal Spacing: Maintain a minimum of 18 feet between mature tree crowns, with increased spacing (20 feet or more) on slopes to reduce the spread of crown fires.
- Vertical Spacing: Create vertical space by maintaining a minimum of 6-10 feet from the ground and ensuring tree branches are not too close to each other to prevent future interference.
- Focus on Deadwood: Remove all dead wood from trees to reduce their ability to burn.
- Professional Arborist: For safe and effective pruning, enlist a certified arborist to assess tree health and execute precise techniques, especially for larger projects.
- Follow ANSI A300: For professional pruning specifications, adhere to the ANSI A300 standards for tree care operations.
Key Takeaways
- Create Defensible Space: The primary goal is to create a defensible space around your home, which is the area managed to reduce the likelihood of a structure igniting from a wildfire.
- Thin Trees: Thin large clusters of trees and remove dead vegetation to break the continuity of fuel and reduce the potential for wildfire spread.
- Understand Your Environment: The exact spacing requirements for trees can vary based on factors like topography and the density of vegetation in your area.
