The Truth About Wildfires In California
By Paul Homewood
WUWT does a nice debunk on the latest attempt to link wildfires to global warming.
Nationally, according to the National Interagency Fire Center, so far this year wildfires are down on recent years, and there is no evidence of any trend to them becoming worse.
There is no state by state analysis for the YTD, but the Interagency has annual data for California since 2002. There are the usual ups and downs, but no obvious trends.
The study quoted by the LA Times is, naturally, all based on computer modelling, but perhaps we should pay more attention to what the forestry experts themselves have to say.
This is what the California Department of Forestry and Fire Protection wrote in their Environmental Impact Report back in 2012. (My bold)
Over millennia, fire has played an integral role in regulating the spatial pattern, composition, and structure of California’s natural resources. With its Mediterranean climate, productive soils, and frequent ignitions from lightning and Native American peoples, fire has been an endemic force shaping the landscapes of California. From coastal grasslands to sub-alpine forests to the Mojave Desert, fire has been an active ecological agent in almost all vegetated areas.
Fire provides an essential ecological function by cycling nutrients, changing plant composition and structure through mortality and fire induced regeneration, modifying habitat for wildlife, and increasing forest health by consuming fuels, thereby making forests less susceptible to unnatural fire severity, pests, diseases, drought, and pollutant stresses. Many tree and shrub species depend on fire to expose bare mineral soil and create gaps for seedling establishment and reduce shade-tolerant competition.
Fire helps maintain a mosaic of habitat conditions in the landscape and preserve biodiversity. Within fire adapted ecosystems, many common plants exhibit specific fire-adapted traits such as thick bark and fire-stimulated flowering, sprouting, seed release and/or germination (Chang, 1994). Some understory shrubs and herbs require the direct effects of fire (heat and/or smoke) to stimulate germination. Where fire return intervals were short, such as ponderosa pine forests, surface fires of low intensity removed seedlings and saplings, consumed accumulated tree litter and downed woody material, and accelerated the return of nutrients to the soil. In frequent fire-adapted communities this maintained an open, park-like forest stand with a continuous ground cover of grasses, herbs, and shrubs beneath the forest canopy (Kaufmann and Catamount, [nd]; Parsons and DeBenedetti, 1979).
For purposes of analysis, the history of wildfire in California can be loosely categorized into pre-European settlement fire regimes and post-European settlement fire regimes, especially the last fifty years where rigorous fire suppression efforts have been undertaken.
Natural fire regimes that existed prior to European settlement in California (pre-1700) involved a wide range of fire frequencies and effects on ecosystems; roughly one-third of the State supported frequent fire regimes of 35 years or less. Some areas likely burned on an almost annual basis. Pre-European settlement fire patterns resulted in many millions of acres burning each year, with fire acting as a major ecological force maintaining ecosystem vigor and ranges in habitat conditions. The pre-settlement period is often viewed as the period under which the “natural” fire regime standard for assessing the ecological role of fire developed.
In the suppression (modern) era, statewide fire frequency is much lower than before the period of European settlement. Between 1950 and 2008, California averaged 320,000 acres burned annually, only a fraction of the several millions of acres that burned under the pre-settlement regimes.
Before the twentieth century, many forests within California were generally open and park like due to the thinning effects of recurrent fire. Decades of fire suppression and other forest management have left a legacy of increased fuel loads and ecosystems dense with an understory of shade-tolerant, late-succession plant species. The widespread level of dangerous fuel conditions is a result of highly productive vegetative systems accumulating fuels and/or reductions in fire frequency from fire suppression. In the absence of fire, these plant communities accrue biomass, and alter the arrangement of it in ways that significantly increase fuel availability and expected fire intensity. As such, many ecosystems are conducive to large, severe fires, especially during hot, dry, windy periods in late summer through fall. Additionally, the spatial continuity of fuels has increased with fewer structural breaks to retard fire spread and intensity. The increased accumulations of live and dead fuels may burn longer and more completely, threatening the integrity and sustainability of the ecosystems.
Species composition within these forests is also rapidly changing. Plant and animal species that require open conditions and/or highly patchy edge ecotones are declining and streams are drying as evapotranspiration increases due to increased stocking. Additionally, streams are being infiltrated by silt and debris following high severity fires, and unnaturally severe wildfires have destroyed vast areas of forest (Bonnicksen, 2003). Some insects and disease have reached epidemic proportions in parts of the State and forest conditions are conducive to more outbreaks. The understory of these once open forests is now dominated by smaller shade tolerant trees that would have previously been thinned and/or consumed by fire.
As Ristvan points out:
There is another part to the story. Only the last 30 years were looked at. Annual forest fire acreage actually declined steadily from a peak in the 1930s until the 1980s, when fire suppression caused fuel loads to grow and acreage started to expand again. Nothing to do with climate change. Everything to do with Smokey Bear and poor forest management.
David South, Professor of Forestry at Auburn University, made this case in a powerful testimony to Congress in 2014 – details here.
He included this graph, which could not better sum up what has been happening: