The Crestone Eagle • July, 2021

To prune or not to prune

by Daniel S. Johnson,


One of the questions I’ve heard recently concerning fire mitigation is about pruning ladder limbs. The lowest limbs on a tree commonly allow fire to climb into the higher branches, then into the crowns. With a strong wind, fire can jump from tree top to tree top without ever touching the ground again in a running crown fire.

It has been a best practice for decades to remove the lowest limbs up to a height of 2 1/2 times the height of the surface fuels beneath them. In our region, this is mostly grasses, weeds and brush models. So, if the grasses under a tree are 18” high, branches must be raised to around 4 1/2 feet. Pinyons and junipers often kill grasses beneath them by a layer of duff, needle castings which build up over the years and compost slowly. The duff layer can carry fire to a height of 1 foot or slightly more, requiring the lowest limbs to be removed up to 3 feet to be safe.

To prune properly, make the cut ½” to ¾” from the trunk or larger branch you are removing the smaller branch from. This will help the tree to heal. Do not leave long staubs which will bleed more.

With proper pruning, a fire passing through your property should stay on the surface in the grasses or duff with only a few isolated trees torching off. The effectiveness of this technique is diminished if neighboring lots have not been pruned to Firewise standards. A crown fire coming off an unmitigated lot can take out homes upslope as if they were never treated.

This is one reason we thin out smaller trees which are misshapen or leaning, trying to find sunlight, in an attempt to get back to the historic spacing of 20-30 feet between old growth trees. The other major reason is that the root spread beneath a tree is usually as large or larger than the tree we see above ground. Properly spaced trees barely touch roots, while unnatural overgrowth creates unhealthy forests of crowded trees in competition for sunlight, nutrients and water. Stressed trees are more susceptible to wildfires, diseases and insects.a

A pinyon pine rejects its lowest branches, making it less available to burn. Pruning the dead branches helps even more.

I’ve recently heard a theory propounded locally that says removal of lower limbs will allow sunlight to dry out and kill a tree. In actuality, many species of trees reject their own lower limbs naturally, which ultimately protects them from surface fires. All trees, with lower limbs or not, are affected by sustained drought but our local P&J forests are good at retaining water in the roots under the protection of the duff layer (natural mulch). I only suggest removing the duff layer if a fire is imminent and, even then, only pull it back a foot so you can replace it if the fire does not reach the trunk.

With fire season solidly upon us, many of our fire mitigators will be called to work on large national fires soon. We have tried to get everybody who has called an assessment and an action plan for protecting their house, but folks are calling every day now that there is smoke in the area. If you wish to mitigate around your own house, please watch the YouTube video, Preparing For Wildfire, by Daniel S. Johnson, to show you what we look for and how to remove certain hazards. Even if we can’t get to you until the fall, you can call me at 719-480-9764 to get on the waiting list. And please let your county commissioners know that you are in favor of funding our program again if further grant money comes available.