Hazard Tree Mitigation

How Much Risk is Acceptable?

If absolute maximum safety is the goal and no risk is acceptable, don’t bother doing an inspection.  Just cut all the trees down near any targets, or eliminate the targets.  After all, any tree could fall.

But in the real world, we balance the risks posed by trees with the benefits they provide.  The manager or owner, in consultation with a forest pathologist or other hazard tree expert, must decide what level of risk (hazard rating) they can accept.  This decision can be made:

  • Before inspection.  If there are many trees to be inspected and efficiency is desired, this could be a useful approach.  Trees at and above that level can be marked for treatment during inspection.
  • After inspection.  This allows for a more informed decision. The manager will know how many trees there are at each hazard rating, the species, the size of the trees, and what kinds of defects are involved.

Approaches to Treatment/Mitigation

Tree removal is overwhelmingly the most common approach and will likely remain so, but sometimes it is worth considering other options. These possibilities should be considered in some cases:

  1. Pruning can take care of large dead branches and tops, though it is expensive, requiring a tree climber or bucket.
  2. Topping. This means cutting off the live crown or more, leaving a partial snag that is short enough that it will no longer reach the target or it will likely ‘melt’ in place rather than fall over. An experienced tree climber/sawyer is needed, but leaving residual stem provides:
    1. tree-like, vertical structure where it is needed because of lack of trees
    2. may provide esthetics of old-growth forest appearance
    3. target for those who must practice their hatchet-throwing and chopping
    4. wildlife habitat
  3. Removing target. This means closing certain campsites, trails, roads, moving structures, and in some cases entire sites. These measures are often necessary in the short term when serious hazards are discovered and other treatment is not immediate. But sometimes they are reasonable long-term solutions. For instance:
    1. Campground capacity greatly exceeds demand anyway.
    2. Very large trees that have great esthetic, wildlife, or even historical value.
    3. Resources are simply not available for active forms of treatment.

Finally, a pitch to consider another nontraditional practice. Normally hazard trees, after felling, are removed from the site. Certainly most of them must be removed to clear roads, etc. However, consider leaving some large logs on the site in positions where they will not interfere with designated sites and traffic. If the trees are being sold, cull logs can be used. Benefits:

  1. Give campers targets for chopping with hatchets and such.
  2. Break up excess traffic, allowing ground vegetation to recover.
  3. Provide protected sites along logs where tree seedlings can establish without being trampled and, where necessary, some protection from the sun.
  4. Some consider it an esthetic benefit. Many campers prefer sites with large logs, using them for benches.
  5. Over the long term, decaying logs greatly benefit soil properties by adding organic matter, improving moisture holding capacity and countering the negative effects of soil compaction.

Caveats:

  • Certain bark beetles or disease vectors may breed in downed trees. Obviously this needs to be taken into account.
  • Downed trees may be used by campers for firewood. In that case, only larger logs may be left after a year or so.