This week Leonard and I revisited the Cove Fire site that we are monitoring along Modoc National Forest Road 40N11. The Cove Fire in late July and early August of 2017 burned over 30,000 acres in Modoc County CA, including parts of the Modoc National Forest.
On this trip, since much of the flora is not actively growing during the winter, we particularly noticed the burned and scorched trees, mostly ponderosa pines, incense cedars and Oregon white oaks. Some trees were not burned at all, others were totally consumed by the fire and others displayed varying degrees of crown (needle and leaf) scorch. We began to wonder which of the damaged trees will survive.
The ability of a conifer to withstand fire damage depends on its bark thickness, the needle length and thickness, the root depth and bud size. The amount of damage to the roots, trunk and crown through heat, scorch and burn determines whether a tree will survive.
Many of the ponderosa pines (Pinus ponderosa), to which this post will be confined, were completely undamaged or scorched, even though nearby trees were badly scorched or completely burned. The unscorched tree will probably survive while the burned tree definitely cannot survive.
Generally most ponderosa pines with zero to less than 50% crown scorch will survive while trees with 90% or 100 % crown scorch may survive if they are over 9 inches in diameter and the fire is of low to moderate intensity.
Ponderosa pines do not sprout from underground roots undamaged by the fire, yet they are uniquely able to survive wildfire injury. Some of their roots go very deep. Although the shallow roots may be destroyed, the deeper roots can survive a fast-moving fire.
If about 25% of the cambium (the portion of the tree under the bark that adds woody growth) is damaged, then the tree will not survive. Ponderosa pine bark is very thick (1″ to 3″) with a plate-like structure that resists heat and insulates the cambium from the injurious heat, aiding in limiting fire damage.
The cambium at the base of the tree on the left in these pictures is scorched while the ponderosa pine on the right shows no obvious cambium damage and thus has a better chance of survival.
Bud damage also is a factor in ponderosa pine survival after a wildfire. The buds occur at the terminal ends of branches and are responsible for the following year’s growth. If a wildfire occurs in the early summer before bud development, the tree’s survival is compromised. By late summer and early fall buds have formed. If these buds are not damaged by a late season wildfire, the chance of the tree living is increased. The needles of ponderosa pines are clustered and long, providing some protection to the buds.
Will this tree with crown and bark scorch survive the Cove Fire? Leonard and I will be interested in following certain scorched trees to see if they remain alive.
More information on the Cove Fire can be found in earlier posts including: Ponderosa Pine Regeneration on 12-11-17, Resilience on 08-28-17, Recovering on 10-06-17, and Reaction to Stress on 10-09-17, among others.