Window on Nature
By Lowell & Kaye Christie, F47246
August 2005
Naturally occurring wildfires have been caused by lightning and volcanoes for millions of years. However, archaeologists have found evidence that parts of North America have been intentionally burned for more than 5,000 years. Early Americans periodically set fires to thin the forests so they could spot game animals, grow edible plants, and just get some elbow room.
Since the landscape burned periodically, many of the plants and animals became genetically adapted to fire. These species, also known as pyrophytes, still depend on periodic fires to survive.
Early settlers from across the Atlantic Ocean didn’t realize the importance of setting intentional fires and brought the practice to a halt by the middle of the 18th century. But now, after 2-1/2 centuries of fire suppression, some of the plant and animal species that rely on fire may be destined for extinction. The idea of setting a fire to benefit native plants and animals is a tough concept to accept, especially when the burn is scheduled for an area near you. The natural human reaction is to think, “Quick, call the fire department!” But there are considerations beyond our own needs.
Periodic burning brings tangible benefits. For one thing, ashes provide terrific nutrients for the soil, allowing fire-adapted plants to grow with more gusto and to produce bigger, brighter flowers, resulting in more and better seeds.
Intentional (controlled) burns are used to prevent the domination of undesirable non-native plants, as well as to stimulate the native ones. These fires also help to clear dry material that could potentially act as kindling for a more dangerous wildfire. Besides enriching the soil, it lengthens the growing season by raising the ground temperature.
No matter where you live “” except in the middle of a city, perhaps “” you can see where fire-intolerant, non-native plant species have gradually overwhelmed the natives. Once-natural areas have become dense thickets with very little diversity. Fire is needed to keep these plants under control. It’s impossible to completely revive the look of the past, but at least what remains can be protected.
During your travels you probably have come across recently burned areas. Seeing the scorched land can be very depressing. We live near Yosemite National Park, where less than a decade ago wildfire swept across the park’s west side. But come spring, the burned areas began to heal. Solar heat absorbed by the blackened surface warmed the soil early on in the healing process, making the vegetation respond rapidly, with seeds sprouting and still-living shrubs sending up shoots. Each spring is greener than the last, but unfortunately, the acres and acres of dead pine forest will take much longer to regrow.
To survive a fire, a healthy tree must insulate itself from the heat of the flames. Bark thickness is a major factor in determining fire resistance. In the West, ponderosa pine, Douglas fir, longleaf pine, and the giant sequoia are examples of trees whose thick bark provides both insulation and fire resistance.
Small woody plants and shrubs usually have thinner bark, so they rely on their thick roots and the insulation of the soil to protect them. That way, come spring, many can produce new growth.
A special survival method used by seed-bearing species is to retain their seeds until a fire stimulates their release. A number of pine species have pinecones that don’t open for many years, because they require the heat generated by a fire.
A unique climatic condition in Southern California is caused by the Santa Ana winds “” hot, dry blasts from the desert that can dry out vegetation. Those winds set the stage for massive and destructive blazes in the autumn. Entire mountainsides once covered with healthy forests can become blackened in a day.
The destruction would be more than a little depressing except for one thing. The following spring, fire-adapted plants spring into action, producing an incredible display of wildflowers that spread across the charred soil, while the surviving shrubs and trees produce surrounding greenery.