Evidence, Exaggeration, and Error in Historical Accounts of Chaparral Wildfires in California

Abstract

For more than half a century, ecologists and historians have been integrating the contemporary study of ecosystems with data gathered from historical sources to evaluate change over broad temporal and spatial scales. This approach is especially useful where ecosystems were altered before formal study as a result of natural resources management, land development, environmental pollution, and climate change. Yet, in many places, historical documents do not provide precise information, and pre-historical evidence is unavailable or has ambiguous interpretation. There are similar challenges in evaluating how the fire regime of chaparral in California has changed as a result of fire suppression management initiated at the beginning of the 20th century. Although the firestorm of October 2003 was the largest officially recorded in California (approximately 300,000 ha), historical accounts of pre-suppression wildfires have been cited as evidence that such a scale of burning was not unprecedented, suggesting the fire regime and patch mosaic in chaparral have not substantially changed. We find that the data do not support pre-suppression megafires, and that the impression of large historical wildfires is a result of imprecision and inaccuracy in the original reports, as well as a parlance that is beset with hyperbole. We underscore themes of importance for critically analyzing historical documents to evaluate ecological change. A putative 100 mile long by 10 mile wide (160 x 16 km) wildfire reported in 1889 was reconstructed to an area of chaparral approximately 40 times smaller by linking local accounts to property tax records, voter registration rolls, claimed insurance, and place names mapped with a geographical information system (GIS) which includes data from historical vegetation surveys. We also show that historical sources cited as evidence of other large chaparral wildfires are either demonstrably inaccurate or provide anecdotal information that is immaterial in the appraisal of pre-suppression fire size. Since historical evidence is inadequate for reconstructing a statistical distribution of pre-suppression fire sizes to compare with post-suppression data, other more propitious methods of evaluating change are discussed.

The impact of over 100 years of wildfires on mercury levels and accumulation rates in two lakes in southern California, USA

“…4d), which was one of the largest and longest fires in the Angeles National Forest (240 km 2 , burned all summer), and occurred within 20 km of Crystal Lake (Minnich 1987;USDAFS 2008). It is possible the perimeter of the fire was closer to the lake, as the location and area burned were not accurately recorded at the time of the fire; more precise record keeping did not begin until the instigation of fire suppression management in 1895 (Goforth and Minnich 2007). RDL-3 (1938) was the only sediment layer not associated with a fire; however, a spike in total carbonate (32-34 cm, LOI, 950°C [18%, Fig.…”

“…Based on the age model, the sedimentation rate between 1950 and mid-1960s (32-52 cm) was 1.4 times greater compared to the mid-1960s to the present (0-31 cm) (1.5 cm year -1 vs. 1.1 cm year -1 ), indicating rapid accumulation of finer grain particles as lake levels increased, which led to increased Hg concentrations. Table 3 Within Crystal Lake, comparison between dates for rapidly deposited layers (RDLs, i.e., turbidites) estimated from the 210 Pb age model ± 1 standard deviation (sd), and historical events within the lake's drainage basin, including fire history in the last century (US-DAFS 2008), store construction (Conrad 2003), and the 1878 unnamed fire (Minnich 1987, Goforth andMinnich, 2007) Two large fires occurred \10 km from Big Bear Lake, (1970Bear Fire, 1999 (Table 1a; USDAFS 2008). There was a spike in Hg levels near the top of the core (Fig.…”

Granitic Boulder Erosion Caused by Chaparral Wildfire: Implications for Cosmogenic Radionuclide Dating of Bedrock Surfaces

“…many fires that were slow moving (Minnich 1987). These fires would last for weeks and months, were small in area compared with recent extreme wildfires, and resulted in a patchwork of chaparral stands of differing ages (Minnich 1987;Goforth and Minnich 2007). The slow-moving wildfires are characterized by braided, reticulate configurations with numerous islands of unburned cover (Minnich and Chou 1997).…”

Degraded or just dusty?: 150 years of ecological change in inland eastern Australia

“…Across rangelands in Australia and North America, where the spread of European pastoralism was omnipresent and abrupt, recurring arguments about the cause and magnitude of landscape change are frustrated by the rarity of records that predate this momentous biogeographic watershed (Swetnam et al 1999;Witt et al 2000;Goforth and Minnich 2007;MacDougall 2008). In the absence of reference sites unaffected by pastoralism, ecologists have turned to the historical record to better understand contemporary ecosystems and their dynamics (Swetnam et al 1999;Foster 2000;Bowman 2001).…”

“…In the absence of reference sites unaffected by pastoralism, ecologists have turned to the historical record to better understand contemporary ecosystems and their dynamics (Swetnam et al 1999;Foster 2000;Bowman 2001). Historical sources provide a temporal perspective far exceeding that enabled by long-term field studies, and are especially valuable where ecosystem alterations or upheavals predated formal studies (Jackson et al 2001;Goforth and Minnich 2007;Luiz and Edwards 2011). Historical ecologists have employed a diverse array of sources spanning timescales from millennial to centennial and decadal, encompassing natural and documentary sources.…”