It started in the early morning of Augwhen the remnants of Tropical Storm Elida swept across Central California and generated nearly 11,000 dry lightning strikes. The CZU Lightning Complex Fire was not a typical redwood fire. Furthermore the growth in height of a tree and its ability to sequester new carbon as wood is temporarily impaired until it has recovered from the fire, typically requiring multiple years if not decades.
A severely burned forest releases large amounts of stored carbon from its branches, understory vegetation, litter layer, and soil. On the other hand, old-growth Douglas-firs will likely succumb to the fire and their falling may knock down other trees including redwoods. Dormant buds beneath the bark survive and send out new branches so that a new, (albeit thinner) live crown would form. Mature trees also have a thick bark layer that protects the cambium layer inside the trunk so that even a crown fire that burned all the branches off the trunk would not kill the tree. Redwoods themselves are resistant to death by fire, having the ability to send up sprouts from the root collar. Consequently, these types of fires did not have serious long-term adverse impacts on the redwood forest biotic community. The unburned areas along with the unburned down logs would serve as refuges from the fire for small animals, invertebrates and mycorrhizal fungi. These fires would typically skip over areas thereby leaving behind a mosaic of burned and unburned patches. Most importantly, they served to reduce the fuel build-up on the forest floor and remove ladder-fuels that, if allowed to persist, could carry fire into the tree canopies. They would burn up the litter layer but not be so hot as to completely sterilize the organic soil layer below. They would scorch the large down logs on the forest floor but not devour them. They would blacken the thick outer bark of the old-growth Douglas-firs but not kill the trees. Only rarely would they enter the redwood and Douglas-fir tree crowns. Until the recent period, most fires would stay low and burn with much less severity than the CZU fire. Fire suppression has likely led to an increase in highly flammable fuels which has been aggravated over the last 20 years by the deaths of many tan oak ( Notholithocarpus densiflorus) trees in the understory layer due to arrival and persistence of the Sudden Oak Death pathogen.
In recent times, at least up until the 2000s, fires in the redwood forest have been suppressed, and fire frequency lowered to about one fire every 130 years according to a study by Greenlee and Langenheim (1990). During the early Anglo-American period (1848 – 1929) the fire return interval was between 20 – 50 years as much of the forest was clearcut and fire was used as a tool to clear brush and debris and ease the extraction of downed trees. Fire frequency increased during the Aboriginal period (11,000 BP – 1792 AD) to a value between 17 and 82 years apart as fires set by indigenous people to promote and retain grasslands sometimes spread into the redwood forest. Lightning was the primary source of ignition, but lightning was a rare event in the Santa Cruz Mountains. Prior to the arrival of Europeans, fires in the redwood forest were mainly low to moderate intensity ground fires that burned the litter layer, forest floor vegetation, shrubs, and small trees, but seldom entered the canopy of the dominant redwoods and Douglas-firs. Redwoods are adapted to fire, but their forest associates are not. They’ve told the public that redwoods need fire to reproduce or that redwood forests are well adapted to fire. Many local land conservancies and conservation groups that focus on redwoods have down-played the seriousness of this fire.
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