The Impact of Excessive Fire Chaparral on its way to being type-converted to weedy, non-native grassland. The site in the image above is east of Alpine off Interstate 8 in San Diego County. The far left shows an old-growth chaparral stand last burned during the 1970 Laguna fire. The middle/left of the picture shows an area recovering from the Viejas fire of January 3, 2001. It is composed primarily of chamise, deerweed, and several other shrub species. To the right is a portion of the Viejas fire scar reburned in the Cedar fire October, 2003. As you can see the Cedar fire scar is now filled with non-native grasses. The majority of the resprouting shrubs have been killed and no obligate seeding species, such as Ceanothus, are present. The interval between the two fires was too short, causing the elimination of the chaparral plant community.
Aside from development, there are three basics threats to the chaparral ecosystem in California that ultimately lead to the type conversion of native shrublands to non-native weedlands.
Misconceptions about chaparral have the potential of being the most dangerous because they lead to irrational public policy that promotes destructive land management practices such broadscale destruction of native shrublands through prescribed burning, grinding, and the spraying of herbicides. In fact, the US Forest Service has recognized the threat of increasing fire frequencies on chaparral in their latest Leadership Intent policy document for California.
Please see our Help! CalFire EIR page for details on a proposed policy that unnecessarily targets millions of acres in California for clearance operations that will likely lead to type conversion.
TYPE CONVERSION OF CHAPARRAL
What is Type Conversion?
A common misconception is that chaparral is a "fire-dependent" plant community that supposedly needs to burn on a regular basis to remain healthy. It's much more complicated than that. Chaparral is not a simple, homogenous ecosystem. Each type of chaparral responds differently to fire depending on the species present, angle and direction of the slope on which it grows, local climatic conditions, and the frequency, intensity, and seasonality of the fire. The one factor all types of chaparral have in common, however, is that they are all sensitive to fire intervals shorter than 15-20 years. This is the minimal amount time it takes for a burned stand to recover properly and set enough seed in the soil to be able to bounce back after the next fire. As fire frequencies increase due to human caused ignitions, the intervals between fires have been contracting, causing the complete elimination of chaparral in some areas and serious degradation in others.
As can be seen in the photo above, non-native grasses quickly invade frequently burned areas, making it extremely difficult for a healthy chaparral to return. Areas where native shrublands have been replaced by non-native weeds include:
North side of Highway 52 in San Diego County next to between Lakeside and Mission Trails Regional Park. What was once a pristine stand of chamise chaparral is now being type-converted to non-native, weedy grassland. The 2003 Cedar fire probably sealed much of the area's fate.
Along State Highway 60 between Moreno Valley and Beaumont in Riverside County (see photo #4 below).
The foothills to the north of Interstate Highway 10 between San Bernardino to Banning in Riverside County.
Box Springs Mountains east of the city of Riverside (see photo # 3 below).
The east side of Interstate Highway 15 between Murrieta and Corona.
The hills along State Highway 91 between Corona and the 241 toll road.
Much of the landscape between Buellton and San Luis Obispo on State Highway 101.
Look along canyons, fence rows, and steep hillsides (where the cattle can't go) and you will see the remnants of the California sage scrub habitat that was likely the dominant plant community in this area prior to human arrival. The older oaks remain, but they are surrounded by a carpet of alien grasses. Much of the summertime golden hills landscape on the central coast is actually a disturbed ecosystem dominated by invasive weeds (see photos #5 and #6 below).
Also see our Desert Fires page for details concerning type-conversion in desert ecosystems.
More Examples of Type Conversion
1. Nearly the entire chaparral and coastal sage scrub ecosystem that once existed here has been eliminated and replaced by non-native weeds. The Witch fire swept through this area in 2007. Photo taken a year later. Location: Clevenger Canyon along State Highway 78 between Escondido and Ramona.
2. Remnants of chaparral are struggling to recover, surrounded by non-native weeds. Closely examine the area in the center of the photo where the shrubs are resprouting after the 2007 Witch Creek Fire. Notice there are few weeds in this area. The absence of weeds can be attributed to the intense heat released when the chaparral burned here. The heat eliminated any non-native weed seeds that may have been present. This is why hot, intense fires are beneficial in chaparral ecosystems. Location: a north facing slope in Clevenger Canyon (also see photo #1 above).
3. Box Springs Mountains, Riverside County. Excessive fires have eliminated native shrublands in these mountains and replaced them with an ugly coating of invasive weeds. Scenes dominated by weeds and concrete are becoming more frequent as poor land use policies continue to encourage habitat loss.
4. The wastelands along State Highway 60 in Riverside County. All that is left of the rich sage scrub and chaparral ecosystems that once decorated these hills are isolated clumps of sugarbush surrounded by a sea of invasive weeds. Fires often burn here every year because annual weeds create highly flammable "fine" fuels.
5. The impacts of destroying native shrubland ecosystems and replacing them with weeds go beyond just the visual loss of nature. Notice the slumping of the hillside on the right hand side of this photo. With the removal of native plant species that provide vital watershed protection via deep roots and vegetative cover, massive amounts of erosion can take place. This loss of watershed also causes drastic reductions in the underground water table since most of the rain water runs off instead of slowly filtering into the ground. Photo taken on US Highway 101 near Lompoc.
6. Cattle trails and the ghost of overgrazing and overburning past. The few oaks left on this hill were likely surrounded by a rich carpet of sage and chamise prior to the introduction of abusive land management practices. Near Buellton, California. Note chaparral covered hillside in the background and cattle trails on hill to the right. We obviously need to provide grazing land for livestock, however, we also need to acknowledge the damage grazing and excessive fires can have on the landscape and prevent such damage from spreading into healthy ecosystems.
7. Type conversion in the Trabuco Ranger District of the Cleveland National Forest. This is a fuel break along the ridgeline of the Santa Ana Mountains. All native vegetation has been eliminated by crushing and repeated fire. The effectiveness of this type of habitat elimination in terms of preventing the spread of wildfires is highly questionable because ridgelines are natural fire breaks themselves. However, the natural resource damage is unquestionably significant.
Quote from above paper: "At the interface between human development and chaparral vegetation, desirable management from biological and slope stability perspectives argues not for relatively short rotation hazard reduction burning, but for improving characteristics of the built environment (defensible space, structures, landscaping, safe evacuation means, etc.), in efforts to reduce the perils of fire posed by living near chaparral."
1. The natural fire return interval for chaparral is 30 to 150 years plus (today, there are more fires than the chaparral ecosystem can tolerate - see #2 below).
2. Fires more than once every 20 years, or during the cool season by prescribed fire, can eliminate chaparral by first reducing its biodiversity through the loss of fire-sensitive species, then by converting it to non-native weedlands (called type-conversion).
3. Being dense, impenetrable, and prone to infrequent, huge wildfires is the natural condition of chaparral (it's not the fault of past fire suppression, "unnatural" amounts of vegetation, or environmental laws).
4. The age and density of chaparral has little to do with the occurrence of such large fires (large fires in southern California shrublands are driven primarily by weather, such as Santa Ana winds and drought). 5. Chaparral has a high-intensity, crown fire regime, meaning when a fire burns it burns everything, frequently leaving behind an ashen landscape. This is in contrast to a "surface fire regime" found in dry Ponderosa pine forests in the American Southwest. Although there can be high-intensity patches where all the trees burn (high-severity), these fires typically burn at low-intensity, consuming mostly just the understory and leaving the larger trees unharmed except for occasssional fire scars.