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Drought and Wildfire

The current Californian drought presents more problems than are apparent at first glance.

In addition to causing problems for farmers, trees and lawns, the drought is that it predisposes the state to more frequent and more intense wildfires.

Not All Forest Fires Are Created Equally

It is important to distinguish between the different types and spreading characteristics of wild fires, as each has a different effect on the forests.

Ground fires are usually of low intensity, and although they can deplete the rich leaf litter and nutrients of the floor, they are not as hazardous to mature trees. Ground fires burn fuels found below the surface litter.

By contrast, surface fires use fuels found on the surface of the ground, including leaf litter, pine needles, bark, twigs, and fallen branches. Surface fires are of higher intensity than ground fires are, yet they are not as intense as crown or canopy fires. Crown fires are incredibly intense, but they typically require strong winds and plenty of fuel to perpetuate.

Forest Fires Are Natural

Wildfire is a natural component of many western ecosystems, and most native plants and trees have evolved mechanisms for perpetuating the species despite the challenge. For example, giant sequoias (Sequoiadendron giganteum) and ponderosa pines (Pinus ponderosa) have evolved thick bark to help protect their trunks from the heat of forest fires.

Other trees, such as Jack pines (Pinus banksiana), have evolved cones that only open and release seeds once they are exposed to the high temperatures of a fire. By releasing their seeds at this time, the seeds find a bare forest floor, which they need not share with competitors. Many other trees, such as coast live oaks, depend in part on the caching habits of jays, squirrels and other creatures to ensure some of their acorns survive fires, and can sprout in the aftermath.

Paying for the Past

One factor that contributes to the danger of wildfires is the fire-suppression strategies of the recent past. Operating under a philosophy to suppress all wildfires, large amounts of fuel accumulated in the forests, as routine, low-intensity fires were not allowed to clear out this dead wood. Accordingly, when a fire does occur, this plentiful fuel can cause the fires to grow in intensity. Rather than a low-intensity ground or surface fire, a raging canopy fire develops, which kills a great number of trees – even those that are adapted to fire. Current strategies seek to allow low-intensity fires to burn in a controlled manner, which may help prevent canopy fires.

Special Species

Some trees are especially problematic during droughts. For example, coastal redwoods (Sequoia sempervirens), which typically grow in the fog-drenched coastal regions, often go into decline during droughts, and many die. When they do, they increase the chances of a ground fire – which are normally of low intensity – leaping into the canopy, courtesy of the trees’ dead foliage. Of course, many other species can also help fire to ascend into the canopy, but the size of redwoods increases the potential for problems.

Moving Forward

As reported by Time.com, California state officials have already documented more than 120 wildfires on National Forest land.  To help reduce the chances of severe wildfires in the future, the Forest Service is trying to restore the ecological balance of many areas. This includes, among other measures, removing invasive species and planting natives, many of which have evolved various forms of fire resistance.

Most scientists predict droughts to become more severe, more frequent and longer in duration as the Earth’s climate continues to change. These droughts are sure to cause an increase in the frequency of wildfires, while non-native species and past fire management strategies are likely to exacerbate the fires that do begin.

Therefore, while it makes good sense to do what we can on a local level to address these problems, such as thinning overcrowded forests, taking steps to conserve water and planting native species, it is going to require a global effort to address the problems of climate change, and the sequelae that follow.