Los Angeles Shrub Lands: Why park managers are holding their breaths

By Lily Kerrigan

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If you asked a US Forest manager today about the future of Western landscapes, you may start planning a camping trip to catch a last glimpse. That’s because the forest manager would probably tell a cautionary tale about the future of Western forests, describing a frightening “new normal” that, for all practical purposes, cannot be stopped.

Wildfire in Jemez Mountains, New Mexico; the beginning of the ‘new normal.’ Image: Paul Asman and Jill Lenoble.

Well, maybe that’s overreacting. But, as reported in the journal Nature (Vol 489, 352-354) these gigantic shifts in forest ecosystems describing how the prevalence of uncontrolled, destructive fires will create rapid and unprecedented ecological shifts within Western American forests. By and large, in the United States, hot fires fueled by changing climatic conditions and a history of flawed fire management techniques will render some forest areas unrecognizable, as we know them today. Many forest landscapes will become shrub land, dominated by low-lying shrubs and grasses. Everything we associate with forests (e.g., shade, smells, framed views, etc.) will go out the window.

In California the story isn’t that simple. Recently, Westerling and colleagues (Science, Vol 313, 940-943) modeled the effects of climate change on California wildfires. Using four different climate change scenarios, the authors showed that landscapes (especially the Sierra Nevada) in the Northern part of the state are at extreme risk to wildfire. This is, in part, because forested areas in this region are characterized by a large amount of leaf litter (fallen leaves and bark), which is an ideal source of ignition under the hot and dry conditions (the “new normal”) we can expect from changing climatic conditions. Interestingly, the story for Southern California is much more variable. The same conditions that increase the probability of fire in Northern California can actually decrease the probability of fire in Southern California. In these scenarios, familiar locations within the Los Angeles area such as Griffith Park and the Santa Monica Mountains are 28% less likely to be impacted by a large fire, while landscapes in Northern California are 95% more likely to succumb to a wildfire hazard.

In the Los Angeles area, fast growing, non-native grasses act as a medium for fire to move through. Image: Brian Lee Clements

So why is Southern California at a lower risk of large wildfires than Northern California? While leaf litter is a likely ignition source and one of the major factors when considering wildfire risk in Northern California, the risk of wildfire in Southern California is much more dependent on shifts in climate (i.e., specific cycles of rain, drought). Typified as a Mediterranean climate, plants found in the Southern Californian locale are, by and large, compact, short, and shrubby. Add to this the continuous coverage of low lying grasses, which grow at their peak rate after seasonal rains, one is essentially left with the string leading the charge to a few sticks of dynamite; it is the medium the fire moves along to create destruction. So, while it may seem counterintuitive, an extremely wet season (i.e., El Niño) could herald a season of large wildfires in Southern California, while a prolonged dry spell (i.e., La Niña) would vastly reduce this risk.

But the fluctuations in the outcomes of the risk models discussed above – something perhaps even more frightening than the increased probably of large-scale fires: the uncertainty of future climate conditions in California. While the effects of climate change on temperature are understood, the effects of climate change on precipitation are relatively unknown. With this uncertainty, environmental risk can really only be determined in real-time, putting a cap on our ability to act preventatively to stop fires from destroying both human developments and ecology.

About the Author: Lily Kerrigan is a graduate student in the three-year Landscape Architecture (MLA+3) program at the University of Southern California. She is taking classes at the Dornsife Environmental Studies program to further her Directed Design Research project in the MLA+3 program. Her project focuses on designing environmental resilience in fire-prone landscapes within the urban-wildlife interface in Southern California.

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