Tree plantations (resulting from clearcutting) intensify fires.
-
Fire is a natural component of a forest ecosystem. However, the widespread practice of clearcutting on private lands in California creates conditions for much more catastrophic, less-controllable fires. These high-intensity fires not only destroy wildlife habitat and precious forest resources, but threaten the homes of families and businesses in rural areas.
- Clearcutting negatively impacts the natural balance of fire activity. Clearcutting releases large quantities of carbon dioxide into the atmosphere, thus accelerating the pace of climate change. In turn, climate change is raising temperatures that increase the frequency and intensity of forest fires.
- In the first few years after a clearcut, fire danger is actually low because there is a lot of bare soil and small trees are far apart. But after about 8 years, fire danger increases and fires are likely to burn far more intensely. Plantation trees are very susceptible to fire because they are lower in height and size than the trees they replaced. Furthermore, they are closely spaced, with intertwined branches, and their thin bark is less protective than older trees.
- A recent study by the US Forest Service found that industrial tree plantations are prone to severe, stand-replacing fires. In the 2002 Umpqua National Forest Fire, for instance, “Plantations experienced a disproportionately high amount of stand replacement mortality caused by crown fires as compared to older unmanaged forests.” After a forest fire, government evaluations find that tree plantations have a higher mortality rate and actually spread fire.
Plantation trees are less fire-resilient.
- Clearcutting removes all fire-resilient trees and replaces the entire area with younger trees in plantations, which are a high-fire risk. Over many years, the bark of mature trees thickens and becomes more resistant to fire. In a lower-intensity fire, they naturally lose scraggly lower limbs near the ground but otherwise remain unharmed. Plantation trees are of lower height, have thinner bark, and share a uniform crown, increasing their propensity to combust and spread fire, even in a low-intensity fire.
- Tree plantations comprised of densely-stocked, even-aged stands of young conifers are extremely flammable and vulnerable to catastrophic fire effects. When plantations burn they normally result in 100% mortality of trees, and have no native seed sources to naturally regenerate stands.
Uneven-aged, diverse forests have the best chance of surviving fires.
- A California study clearly suggests that multi-aged, diverse forests (not tree plantations) have a higher probability of survival with less bug infestation and fire risk. Planting mixtures of species, maintaining multi-age classes, reducing tree density, and pruning trees at strategic intervals are examples of cultural practices that could improve timber yields.
- A spatially mixed forest limits the spread of both pathogens and insects. Lower tree densities reduce fuel loads and competition, providing structures that are more resilient to catastrophic events like fire and epidemics. In contrast, a fire that burns in a multi-age diverse forest often leaves behind large older trees with thick bark than can survive the next fire. Even when trees die from a fire, large dead trees are especially valuable as they decay and replenish the soil and foster regrowth.
For fire to gradually be able to return to its natural role of rejuvenating California’s forests, we need to be far more carefully managing prescribed burning in overly dense forests to help consume some of the decades of accumulated fuels and to reduce fire severity when wildfires do ignite. By halting the practice of clearcutting and the resulting even-age tree plantations, California could reduce the risk of severe wildfires.