Scars Link Fire History to Tree Survival
Scars at the base of surviving trees injured by fire record the distribution of fire in space and time. From the outside of a tree, a fire scar is an arc of killed tissue around a portion of the stem, bounded to the outside by ribs of woundwood formed after the fire. Dendrochronologists read the internal record of fire scars in tree rings to establish the extent of past fire and to estimate the environmental conditions that lead to wildfire. Recent research on wood anatomy in ponderosa pine, Douglas-fir, and western larch indicates that fire scars can be hidden by intact bark 8 years after fire injury, which could result in under-reporting by visual field surveys. Rather than being just a passive record of fire exposure, scar formation is a survival process involving tradeoffs of growth and defense. This dynamic process enables individual trees to witness and record multiple, even many, fires throughout long lifespans. The tradeoffs are investment strategies that parallel others in tree development such as safety versus efficiency in water conduction and growth versus protection from herbivory. Understanding these dynamics in wood structure and function will enhance the development of tools both to assess fire history and to understand mechanisms of long-term tree survival in stressful environments.
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