Trees Tell Us Much About Fire: What Will We Do About It?
In the Pacific Northwest, trees are abundant and wildfire is a constant presence. In fact, the region was beset with monumental wildfires in the summers of 2014, 2015, and 2017.
These days, wildfires are often catastrophic, but historically, fires were integral to a healthy ecosystem. Sparks generated by lightning went untamed. Native Americans also used fire to care for the land.
In the late 1800s, settlements, road-building, and livestock grazing began to impact the region’s forests. Logging removed the most valuable and fire-resilient trees, such as giant ponderosas in the east Cascade slope. After 1910, fire suppression became the norm for forest management, largely in response to catastrophic fires that tore through the landscape and claimed many human lives. This meant putting out any and all forest fires as quickly as possible. More recently, scientists and forest managers have reconsidered this strategy of excluding all fire.
Meet the Ponderosa Pine
While no human has lived through the storied history of fire in the region, we can look to an iconic tree to learn about the impact of fire suppression.
The Inner Tree
Imagine if you had your entire medical record, including all your checkups, physicals, and surgeries, inscribed on your skin, such that one look could provide a rough overview of all the times you were injured, stressed, or malnourished. A tree’s rings, which build just underneath the bark as seasons and years pass, are such a depiction. Cutting out a cross section of a tree’s trunk produces a “cookie” that gives us access to this story.
Each of the alternating light and dark rings is a year of tree growth. Although each ring will be naturally thinner as the tree ages, there is much that tree rings can tell us:
The cookie clearly indicates that the tree experienced regular intervals of fire until 1908, but that this frequency declined dramatically in the 20th century. What does this change mean for trees, and what are the implications for forests?
Living with Wildfire
When a ponderosa pine is young, it is susceptible to fire, but by the time the tree reaches 4 or 5 years, it has begun to develop a thick bark that protects it from low-intensity fires that may sweep through every few years. The same fires remove competition from shrubs and less fire-resistant trees, such as true firs like grand fir, and create the open…
