Peter Hess's picture

Evolution, Fire Ecology, and Climate Change

“Gnats flitted on the warm, dry, summer breeze, some settling on the surface of Pinecrest Lake. It was strangely overcast, as if storm clouds were gathering over the western foothills of California’s Sierra Nevada. However, before long the unmistakable odor of distant wildfire smoke filled the air, and the gnats flying over the lake were revealed to be flakes of ash falling as thickly as snowflakes. Then, as ghostly fragments of charred pine cones and conifer bark floated down, we knew that the Rim Fire was getting close.”

The above is my summary of a story recounted to me by a fellow parent on our sons’ first day of school last week. His family vacation at Pinecrest Lake in Tuolumne County had been abruptly curtailed by the “Rim Fire” that started near Groveland in the Sierra Foothills on August 13. As of September 3 this had become the fourth largest wildfire in California history, scorching well over 235,000 acres.

It’s now late summer in California, and it’s business-as-usual with wildfires. We don’t yet know how the Rim Fire was ignited—perhaps it resulted from a lightning strike or perhaps it had a human cause. But the significant point is this is wildfire season. From now until the first good rainstorm of October, our days are likely to be hot and windy—and we are in our driest year in more than a century.

California is among the numerous places on earth where fire ecologies have evolved (others include the South of France, Australia, and parts of Siberia). California is characterized by mixed forests, brushlands and grasslands, many elements of which are inextricably bound up with fire. Pinus attenuata or Knobcone pine has very hard cones sealed with heavy sap, that can only release their seeds when the heat of a wildfire burning beneath them opens them up. Species of brush that make up chaparral—scrub oak, manzanita, chamise, ceanothus, mountain mahogany, pickeringia—these cannot reproduce easily unless the land is swept clean by fire every quarter or half century.

A fire ecology is an intricately evolved piece of the tangled bank of nature. It supports a great deal of biodiversity, as does a tropical moist forest or a desert or a tundra. The main difference is the way in which it functions with respect to growth and reproduction.

When humans decide to inhabit this ecology without adequately considering how it works, the results can be traumatic. We tend to think of Homo sapiens as invulnerable, as masters of our world. But that is not always the case, as recent disasters such as the Waldo and Black Forest Fires near Colorado Springs demonstrate. Much of the human and property loss involved in those fires resulted from housing developments having been built in flammable brush and timberlands without taking appropriate precautions against fire. These precautions include clearing a defensible space around every house, and having adequate on-site water storage capacity for the safety of fire fighting crews.

Climate change is likely to exacerbate this situation by changing many of the variables influencing fire behavior. Some regions will no doubt experience prolonged droughts (e.g. Arizona, New Mexico, and Colorado), leading to pine and fir beetle infestations that will kill thousands of trees. This increased load of dead and downed fuel will amplify fire potential, and when a fire is started we may find that a changed climate has altered patterns of humidity, air temperature, and wind speed. Fires will burn hotter and more destructively, delaying or even preventing full recovery after an area has been burned.

None of this is to say that humans should not live in temperate dry forests. We love the beauty, peace, and tranquility of living in the woods, and it would be a shame to abandon them outright. But we need to rethink how to inhabit fire-prone regions rationally. Just as there are areas below sea level where it would not be advisable to live in an era of sea level rise and change in hurricane intensity, so there may be areas of fire ecology where it would be wise not to build extensively and without foresight.