Misunderstanding Natural Fire Return Intervals
Many chaparral stands in California are either moderately or significantly altered from their historical fire regime range. Unfortunately, some classification systems currently under development, such the multi-agency Fire Regime Condition Class (FRCC) model and the LANDFIRE project, thus far fail to distinguish between altered by too few or too many fires. Vegetation communities are classified on a scale from 1-3. "1" meaning a community is within its natural fire return cycle, "2" for having missed several natural fire return intervals, and "3" for a community severely out of its natural cycle.
The basic problem of these determinations is they are based on forest studies and are not applicable to chaparral or other shrubland type systems. In addition, the baseline reference point is "pre-settlement" conditions which ignores the potential negative impacts Native American burning may have caused to native ecosystems.
All of the chaparral in California has been classified as either condition class 2 or 3 under these classification systems. Consequently, there is a presumption that all chaparral “needs” to be burned in order to remain healthy and that increasingly rare, old-growth chaparral is “decadent” and has little, if any, resource value. Such perceptions completely misinterpret chaparral ecology and are not supported by current scientific research nor the natural resource or recreational needs of future citizens.
Although the term “decadence” may be helpful to wildland firefighters when describing chaparral stands that have accumulated dead material, it has pejorative connotations and does not reflect our current understanding of the chaparral ecosystem. Specifically,
- The continued ability of chaparral stands nearly a century old to maintain productive growth has been confirmed by multiple investigations (Hubbard 1986, Larigauderie et al. 1990),
- The accumulation of biomass steadily increases for at least 45 years in chamise chaparral (Specht 1969) and probably more than 100 years in other types, especially north facing stands and,
-Shrubs in older chaparral communities are not constrained by limited soil nutrient levels (Fenn et. al. 1993).
While it is true most obligate seeding Ceanothus species will die as a stand reaches 30-60 years of age, others remain an important part of chaparral stands over 90 years old (Keeley 1973, 1975). All of these species have dormant seed banks that ensure their long term persistence in the ecosystem even if fires only occur every century or so. When spaces do appear in the chaparral, living plants quickly fill the void. For example, chamise shrubs that have not experienced fire for at least 80 years continually send up new stems from their base (Zedler and Zammit 1989).
Not only do mature shrubs continue growing over time, but seeds from the majority of species common to north facing, mesic chaparral stands require long fire-free environments before being able to germinate. Moisture protecting shrub cover and leaf litter are needed to nurse the seedlings along. Plants such as scrub oak (Quercus berberidifolia), holly-leafed cherry (Prunus ilicifolia), and toyon (Heteromeles arbutifolia) fall into this category. So rather than being a “decadent” habitat of dying shrubbery, many mature chaparral stands are just beginning a new stage of growth after fifty years of age.
Although chaparral is considered a “fire-adapted” ecosystem and some types do accumulate significant amounts of dead wood, the system certainly does not need human caused ignitions to remain healthy especially in light of the increased number of fires occurring in shrublands today, especially in Southern California. The idea chaparral needs to burn is related more to human misconceptions than any ecological process (Halsey 2005).
Senescence risk, which is the risk of loosing species if fires are too infrequent, has never been demonstrated for any chaparral in any part of the state. In fact, studies show excellent ecosystem post-fire recovery following 150 years without fire. Based on our knowledge of historical burning in chaparral, old-growth stands are clearly within the range of historical variability. Immaturity risk on the other hand, which is the risk of loosing species if fires are too frequent, has been repeatedly demonstrated in countless studies.
Unlike forests, we don’t really know what the natural fire return interval is for each type of chaparral, but we have convincing evidence that fires occurring closer than 15 - 20 years apart can threaten many of them (Zedler et al. 1983, Haidinger and Keeley 1993, Keeley 1995, Zedler 1995, Jacobson et al. 2004). Local extinctions of certain species can also occur if some chaparral types are not allowed to exist past 50 - 75 years. In fact, even the California Fire Plan acknowledges that,
“California has a complex fire environment, with multiple climates, diverse topography and many complex vegetation communities. CDF data on assets at risk to damage from wildfire is incomplete.” And, “unnaturally frequent patterns of fire can overwhelm the inherent ability of many fire adapted species of plants to sustain themselves.”
Applying the right knowledge with the appropriate ecosystem is crucial if we want to properly manage our state’s wildlands. Since chaparral is California’s most extensive plant community, it is prudent to make sure we understand both its particular fire regimes and its sensitivities to changes in those regimes.
There was a period during the last century when one of the primary objectives of land managers was to increase and “improve” range land by eliminating chaparral through increased fire frequency. With growing population pressures, the increasing need for open space, and an expanding wildland/urban boundary, the expectations of land managers is quickly changing. They need to not only protect life and property from wildfire, but also to properly evaluate the demands of competing interests in order to prevent the wholesale elimination of California’s native landscapes.
We need to move away from viewing chaparral as merely fuel and instead begin to appreciate its significant natural resource value.
-Richard W. Halsey
