Chaparral and climate change
What will global warming bring to Earth's most famous (kinda) plant community
Wildfire
Wildfire is a part of our lives for us southern Californians. Sometimes small, burning a few acres of grassland, but just as often huge conflagrations with great columns of smoke billowing up into the sky, one bit of comfort has been that wildfires were limited to late September and October. Outside of that six to seven week period wildfires have been rare or nonexistent.
Rains come to southern California in November and last through March, sometimes April. Six months of drought follow, through summer and early fall. September and October bring the Santa Anas, high-speed winds (sometimes up to 50 to 60 mph or more) that blow in from the desert that are very hot and very dry. Temperatures may be in the 90s Fahrenheit with single digit humidity.
It is the perfect formula for fire: six rainless months punctuated by hot dry winds. Under Santa Ana conditions any spark can ignite the very dry brush. The high-speed winds then spread the flames like, well… wildfire.
Chaparral
Our oak woodlands and pine forests burn during the Santa Ana winds, but most of southern California is covered in chaparral. That is what mostly burns in the wildfires. Chaparral is greatly misunderstood and, ironically, is one of the most seen plant communities ever. Luke and Bo Duke racing their Dodge Charger through Hazard Kentucky? They are actually driving through landscapes of chaparral. Watch the opening of the old TV show MASH. The hillsides of Korea are actually the chaparral landscape outside Los Angeles. For the movies, Roman soldiers have marched through chaparral, and Nazis have driven tanks through it.
Californians have come to associate chaparral with fire, but historically, chaparral didn’t burn much. Chaparral grows in semiarid conditions, and hence experiences few thunderstorms. There are therefore few natural sources of ignition. As well, almost all chaparral plants are evergreen. During late fall, winter, and spring the water content of the plants increases so much that it is next to impossible for chaparral to burn. Without people starting fires, stands of chaparral will grow without experiencing a fire for 60 to 120 years; in some places it may be even longer between fires. When it does burn, chaparral burns in crown fires, in which all vegetation is consumed in the blaze.
Just as forest does not refer to one type of tree or a specific group of trees, chaparral can be a wide array of Western state shrub plant communities. Close to where I live there are hillsides of chaparral dominated by chamise, a short leafed evergreen that can look like a miniature pine tree. A few months ago my wife and I hiked through fields of chaparral dominated by manzanita. Chaparral is also very beautiful. Don’t let anyone tell you any different.
Chaparral and climate change
Scientists recently looked into the possible effects climate change will have on chaparral wildfires in southern California, predicting that climate change will lead to a longer fire season.
The scientists conducted their study at the Stunt Ranch Santa Monica Mountains Reserve, a 310-acre biological study area in the Santa Monica Mountains between Los Angeles and Oxnard. The ranch is overseen by the University of California and is used for such research projects. Plants studied included chamise, manzanita, mountain mahogany, scrub oak, sugar bush, and six other plant species. The scientists published their findings in the Journal Biogeosciences
The scientists looked at three factors brought about by our increase of greenhouse gases: changes in precipitation, increased temperatures, and increased availability of CO2. All three of these affect the water content of plants, and the lower the water content, the more likely it is that a fire will be able to ignite the leaves and branches of a plant. The team measured the chaparral plants water content and then used hydrological modeling to predict the plants’ reactions to future climate predictions.
Though increased levels of CO2 warm the planet, a lot of plants appreciate having more CO2 around, (Psst. Please don’t let this dirty little global warming secret out to your climate change denying friends.), including chaparral plants. More carbon dioxide means that plants can photosynthesize more, and it also helps plants hold onto water in their stems and leaves. The scientists found this to be a mitigating factor in chaparral being prone to burn.
Climate scientists anticipate that much of southern California will actually get wetter, experiencing more precipitation. That increased precipitation, however, is expected to fall outside of the normal rainy season of late fall through the spring, and there will actually be less precipitation during the normal rainy season. Although there will be more water, similar climate induced changes to precipitation have been shown to increase fire frequency in ponderosa pine forests, and the researchers anticipate that the change in precipitation patterns will also be detrimental for the chaparral.
The hydrological modeling indicated that the biggest driver of the chaparral becoming fire prone will be the increased temperatures in southern California. Once they considered all factors, the scientists predict that southern California’s fire season will increase by 24 to 33 days, another month of fires.
Further ramifications
Left out of the scientific paper are the implications for the chaparral as well as the people who live in southern California. Increased fires are real bad news for chaparral. Chaparral plants are adapted to living with fire, but if fires come along too frequently, they do not have the chance to mature and reproduce, leaving an opening for nonnative grasses. The grasses wind up replacing the chaparral, leading to acres and acres of nonnative grasses. This process is called type conversion, and has lead to an enormous amount of southern California being turned into the brown hillsides that are so often seen in movies and television.
The change to nonnative grasslands further exacerbates the fire problem. The grasses quickly dry up in mid spring, leaving tinder that can easily be ignited. This is a far more dangerous environment than the native chaparral, which is resistant to fire.
Increase fires also have grave implications for the people who live in southern California. As so much of the development of southern California sprawls into the chaparral, more fires mean more fire evacuations, higher premiums on fire insurance, and more danger to those who live in these neighborhoods.