Oak Trees & Fire

The survival of oak trees in a wildfire relies on many variables.

Fire ecology explains how the presence of fire affects the growth and survival of various trees and shrubs. Fire plays an important role in the overall selection and adaptions of plants in many types of life zones, including grasslands, pine forests, highland deciduous forests and even wetlands. Oaks are a large group of plants with hundreds of species, so several factors weigh on how a specific species will respond to wildfire.

White Oak in the Eastern Forest

The mature white oak is able to survive moderate fires, but the acorns are often destroyed by a ground fire. Moreover, conditions after a forest fire are often favorable for oak regrowth. Young shoots will sprout from the root crown of a white oak right after a major fire. The soils of a burn area are often hospitable to the next crop of acorns, which seem to easily take seed on burn sites.

Oak Savannahs

The bur oak stands of the Midwestern prairie are highly dependent on grass fires to get established and also for their continued survival. The absence of fire over a long period will lead to a takeover of more shade-tolerant trees, such as maple and basswood. The bur oak benefits from grass fires in two major ways. The bark of a mature tree quickly develops a thick outer layer, which can survive a major fire, while the young shoots will sprout vigorously from the stump or root crown after a fire. Since the arrival of settlers to the prairie and the resulting suppression of fire, the bur oak Savannah has been significantly reduced.

Fire in the California Oak Parkland

California oaks, including the blue oak, canyon live oak, valley live oak and California black oak, thrive amid the grasslands of central California when low-intensity burning is present. The fires help perpetuate the oaks while making it hard for competitive species to gain a foothold. Frequent fires can also aid in the prevention of diseases that are caused by fungi and insects, both of which are a growing problem in the United States.

Live Oaks

Live oaks have a high tolerance for salt, but a low adaptability to fire. As a result, a crown fire in a forest with a live oak canopy will likely result in significant damage to the live oak trees, followed by new growth of different species. However, once the live oak establishes itself as the dominant species, it has several means of discouraging forest fires.
For the live oak, the thick evergreen leaf is the key to keeping fire away. The dense, year-round canopy prevents the growth of a significant understory, which can turn into highly flammable material during a drought. Also, the canopy creates a humid micro-climate, which again acts as a fire deterrent. Finally, the leaf of the live oak burns at a such a low temperature that a ground fire seldom damages the taller trees.

Firewood

Because most oak trees have a dense wood, they burn well when ignited. Of course, the lower the moisture content, the better the fire. For this reason, oak wood is cherished as firewood and a source of heat. Both the red and white sub-families of oak consist of numerous woods with a high BTU/pound rating. Older trees are sometimes cut for firewood, but only after they have been determined to be unusable as lumber because oak boards command a high price at the lumber yard.

References

• USDA Forest Service: Fire Ecology of Live Oaks
• University of Minnesota Forest Ecology Lab: Oak Savanna and Fire
• USDA Forest Service: Fire Ecology of White Oak