Six Reasons Thinning Trees is Good for the Forest

Over the last few months, we have written extensively about the extreme wildfire season in the Pacific Northwest (PNW) and some of the lingering effects that the devastation will have in the near-term. The fires have been in the mainstream news for months, but a recent Wall Street Journal piece about the “controversial” subject of forest thinning and its impact on fire suppression simply gets it wrong.

In the article, journalist Jim Carlton failed to discuss the myriad benefits that regular thinnings have on the overall health of our forests and their peripheral ecosystems, wildlife habitats, and the safety and economic wellbeing of the communities that border them. Indeed, the only controversial practice in this case was giving credence to fringe environmental groups that have no tangible experience in forest management.

As a Forest America rebuttal to the piece noted, the process of thinning has increased in national forests more than 34 percent over the last decade. Forest America adds, “A forest that’s not managed and allowed to grow unchecked crowds out wildlife and becomes a tinderbox, susceptible to forest fires that cost the U.S. government billions to fight each year, to say nothing of the billions in damage to public and private property. State and local governments that once relied on the proceeds from the sale of timber from sustainable forest management, where trees are thinned and replanted, have lost this revenue under pressure from environmental groups who believe trees should never be cut unless diseased.”

Importantly, Forest America also notes that private forestlands suffer fire damage at a much lower rate than public forests, which is due to proper forest management (including thinnings) performed by private landowners. Despite the logistical challenges of maintaining millions of acres of public forestlands, the US Forest Service also understands the value of thinning, which is why the practice has increased within national forests over the last decade.

The Benefits of Thinning

Increased Growth

Private landowners have demonstrated repeatedly that properly managed, working forests have both economic and ecological benefits. Regular thinnings provide an improved environment for maximizing a site’s growth potential, which results in larger, healthier trees and more valuable timber. As a silvicultural practice, thinning allows for the continued growth of the healthiest preferred species within a timber stand while removing the suppressed, diseased and low-vigor trees that will impede the growth of the entire stand. Many of the low-vigor trees in such stands continue to grow at a reduced rate until competition claims them or they are removed via thinning. An integral piece of properly managing the forest is the removal of these trees, which can also serve as unnecessary fuel load during a fire event.  

Improved Utilization

While the economic benefits of regularly removing suppressed and dying trees are minimal, intermediate thinnings do pay for themselves and provide the economic advantage of improving the health of the entire timber stand. Arranged thinnings during growth cycles will yield wood that can be utilized for pulp, chip or pellet operations. Again, while the economic gain may be minimal in this case, the health of the overall stand is improved and thus, the value of the overall stand increases.

Reduced Vulnerability to Disease and Insects

Maintaining proper stand density is essential to reducing tree damage from both disease and insects. As a rule, healthy trees are less susceptible to insect infestation than unhealthy ones. For example, the Southern Pine Beetle (SPB) is the most harmful insect to forests in the US South—an area with a high proportion of pines. The University of Georgia Center for Invasive Species and Ecosystem Health notes that, “Uninfested trees are generally larger, have thicker bark, greater crown/bole ratios, larger crowns, and faster growth rates, and occur in less dense stands. The infested trees were usually located in heavily stocked stands that were under stress.” While other factors can also impact the health of a stand, “high stand density was the most important factor predisposing stands to SPB attack.”

Such pests are not only limited to pine trees in the US South; the US West and British Columbia (BC) are still reeling from a Mountain Pine Beetle outbreak that began in the early 1990s. This insect has since killed roughly 50% of the total volume of commercial pine in the province of BC.

Loblolly and slash pine in the US South are particularly susceptible to certain diseases that flourish in unmanaged forests. Annosum root rot is the most common of these diseases and once a tree in the stand becomes infected, the disease spreads to adjacent trees through root contact. In a dense forest, the root systems of the trees are intertwined providing an easy pathway for this disease to spread.As these systems deteriorate, the trees die and gradually fall over due to lack of support.

Genetic Enhancement

Genetic enhancement can also be achieved through proper and regular thinning. Trees removed in thinnings are usually inferior, diseased or have objectionable shape, which is sometimes due to genetics. By removing such trees early and prior to forest regeneration, the landowner or land manager can minimize the number of trees with undesirable traits in a stand.

Environmental Benefits

Thinnings will alter the environment of the forest, which is a good thing. Thinnings allow the penetration of light, which increases the temperature of soil as well as the availability of moisture and nutrients within the soil. With these changes, forest vegetation flourishes and produces a more favorable habitat for wildlife. Thinnings will invariably reduce the canopy of the forest, which allows a greater amount of rainwater to reach the forest floor as well. 

Fire Prevention

Despite the benefits of thinning listed above, opponents typically rely on the same, haggard argument that is not rooted in environmental science or best forest management practices. These same opponents typically believe that “letting nature take its course” is the preferred method of managing our forests, and they generally eschew any economic gain that might result from forest management and the sale of timber. While Mother Nature has indeed used fire to control forest growth for eons, managing the damage and mitigating the risk that extreme wildfires pose to communities is a challenge that must be addressed. The best available science (and experience) tells us that proper thinnings and controlled burns are the most effective ways to minimize fire exposure.

As the American Forest Foundation (AFF) recently noted, “The good news comes in research showing that managing western forests through thinning and prescribed burns can reduce the impact of these fires. A recent study by The Nature Conservancy and the U.S. Forest Service showed that a 12,000-acre ‘doughnut hole’ within the Carlton Complex fire zone remained untouched by the inferno. The area survived, the researchers believe, because it had been previously thinned and burned. They say that 9.5 million acres of Washington and Oregon forests would benefit from the same management that protected the doughnut hole.”

The AFF continues, “In Arizona, thinned forests and prescribed burns helped stop the huge 2011 Wallow Fire before it reached homes, according to ecologist Morris Johnson of the Pacific Wildland Fire Science Laboratory. ‘As it hit the thinning treatment there’s a transition in the fire type. It went from an active crown fire down to a passive crown fire,’ Johnson says.”

Conclusion

Thinning is an important silvicultural practice that increases the growth potential of the forest as well as the return on investment with higher-vigor and higher-value trees. As noted above, thinning is also a practice that improves the overall health of the forest by mitigating disease and insect susceptibility while minimizing catastrophic fire risk. An unmanaged forest is an unhealthy forest, as well as a potentially dangerous tinderbox of wildfire fuel. To ignore this overwhelming evidence and the advice of thousands of professional foresters throughout the world is irresponsible journalism.