This is a blog about the native conifers of the Pacific Northwest. It is a companion to the Northwest Conifers site. The blog will focus on timely and interesting details about our conifers, their connections to the rest of the environment, and our connection to them.

Wednesday, October 11, 2017

Forest Fires

Recently, the Eagle Creek fire in the Columbia Gorge burned over 48,000 acres. It was disheartening to see so many beautiful trees along familiar trails go up in flame. But it also has been an opportunity to reflect on the nature of forest fires and their effects on forest ecosystems. Here are some reflections.

Forest fires happen. Well, accidents happen, too. But we try to avoid them. We try to avoid forest fires, too. And for the past 100 years, we have aggressively tried to put them out when they do happen. We had good reason to do so. After all, it is a disaster when a forest fire also burns down our house, or when a fire burns trees we were about to use for lumber to build houses. However, when I say that forest fires happen, I want to think about them differently. I want to think about forest fires in a natural forest. The key to thinking about forest fires is that in nature, forest fires happen. That is, forest fires are a natural, recurring event, usually caused by lightning. 

What does it mean? Now, let’s think about the consequences of recurring forest fires: If forest fires are a natural occurrence, then it should be no surprise that the forest has adapted to these fires. And this is just what has happened.   Trees have adapted to deal with fire in different ways. Some grow thick bark that protects them from fire. Others wait for a fire to release their seeds. These seeds are the key to generating a new forest.

Fire is necessary. Forests have not only adapted to tolerate fire. Fire is necessary to the healthy development of the forest. We often think of forests growing to their final mature state and living in perpetuity as old growth. We celebrate old growth as the ultimate state of a forest. We love the huge, mature trees and the diversity of life in a mature forest. However, such a forest is not sustainable. It may live in this mature state for hundreds of years, but eventually it will be altered by fire or some other disturbance. So it’s no surprise that some tree species not only tolerate fire, but depend on it. For example, Douglas fir needs bare earth created by a hot fire for its seeds to germinate. Trees that wait for fire to release their seeds also depend on fire. Many forest types depend on a large fire disturbance to regenerate. 
New life after a fire
Some trees depend on smaller fires to maintain the nature of the forest. For example, ponderosa pines have thick bark that resists fire. Not only do they survive frequent fires, but they depend on those fires to suppress competing vegetation. These fires are necessary to maintain the open pine forest. When we suppress the fires as we have done for over a century, competing shrubs and trees grow and provide so much fuel that, when a fire starts, it burns so hot that it kills even the large ponderosas. In the ponderosa pine forests and many other forest communities, fire suppression has actually caused larger and more destructive wild fires.

Forest ecologists now recognize that fire is a natural and necessary part of a forest ecosystem. So how should we think about the recent fire in the Columbia Gorge? It’s natural to think that our beautiful forests have been ruined. No one wants to hike through such a scorched and destroyed landscape. Well, we can take heart that not all the area the fire touched has been torched. And although some areas appear to be devastated now, they will regenerate. I saw this three years after the Dollar Lake fire on Mt. Hood. We can look forward to observing the same results in the Columbia Gorge. There is much we can learn about a forest when we see how it recovers from a fire. 
Three years after the 2011 Dollar Lake fire on Mt. Hood
Not all fires are natural. On the other hand, the Eagle Creek fire should give us pause. It is significant that this was not a natural fire. It was not caused by lightning. It was, rather, caused by teenagers setting off fireworks. So why is that important? First, the fire was started at the bottom of a canyon. This enabled the fire to quickly race up the steep slope of the canyon and spread from there. Lightning fires are more frequently started on ridge tops at higher elevations where the forest is thinner so the fire starts more slowly. Human-caused fires have also increased the frequency of wildfires. A recent study found that humans started 84% of wildfires in the U. S. over the past two decades. This raises the frequency of wildfires. Natural systems adapted to naturally-caused fire will not easily recover from the increase caused by human-started fires.
Eagle Creek Fire Soil Severity Map
Fire and Global Warming. Now we are faced with another challenge to our forests that is also human caused: Climate warming is changing the behavior of these fires. Warmer temperatures have caused the forests to become increasingly dry in the hot summer. Snow is melting sooner, creating a longer fire season. Over the past 40 years wild fires have become more frequent and more destructive. Wildfires may the biggest threat that our forests face in a changing climate. 

Controlled fires. One strategy for dealing with wildfires is to set smaller controlled fires. The controlled fires remove the excess fuel form the forest, allow the forest to recover, and help prevent hot-burning wildfires. People often object to the smoke caused by controlled fires, but wildfires produce about 10 times the amount of smoke per acre compared to controlled fires. Controlled fires, by their nature can be set at times when weather conditions are conducive to good smoke dispersal and when the winds blow the smoke away from populated areas.

What can we do? We can speak up in favor of forest practices based on recent research for managing forests as an ecosystem that naturally includes fire. This may include the use of controlled fires in some cases. We can point out that these fires are healthy for the forest and healthier for people who live nearby. And most of all, we can avoid starting fires in dry canyons that all too often become destructive wildfires.
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Sources and More Info.
Human-started wildfires expand the fire niche across the United States
How Will The Wildfires Of Today Fuel The Fires Of Tomorrow?
Western Wildfires and Climate Change
Eagle Creek Fire Soil Severity Map
After the Dollar Lake Fire