Late Holocene geomorphic record of fire in ponderosa pine and mixed-conifer forests, Kendrick Mountain, northern Arizona, USA

Abstract

Long-term fire history reconstructions enhance our understanding of fire behaviour and associated geomorphic hazards in forested ecosystems. We used 14C ages on charcoal from fire-induced debris-flow deposits to date prehistoric fires on Kendrick Mountain, northern Arizona, USA. Fire-related debris-flow sedimentation dominates Holocene fan deposition in the study area. Radiocarbon ages indicate that stand-replacing fire has been an important phenomenon in late Holocene ponderosa pine (Pinus ponderosa) and ponderosa pine–mixed conifer forests on steep slopes. Fires have occurred on centennial scales during this period, although temporal hiatuses between recorded fires vary widely and appear to have decreased during the past 2000 years. Steep slopes and complex terrain may be responsible for localised crown fire behaviour through preheating by vertical fuel arrangement and accumulation of excessive fuels. Holocene wildfire-induced debris flow events occurred without a clear relationship to regional climatic shifts (decadal to millennial), suggesting that interannual moisture variability may determine fire year. Fire-debris flow sequences are recorded when (1) sufficient time has passed (centuries) to accumulate fuels; and (2) stored sediment is available to support debris flows. The frequency of reconstructed debris flows should be considered a minimum for severe events in the study area, as fuel production may outpace sediment storage.

Do thinning and/or burning treatments in western USA ponderosa or Jeffrey pine-dominated forests help restore natural fire behavior?

“…Frequent fires maintained relatively open uneven-aged forests with abundant, diverse understories over most of the landscape (Cooper, 1960;Minnich et al, 1995;Brown and Cook, 2006), although some areas may also have experienced infrequent highseverity fires (Sherriff and Veblen, 2007;Pierce and Meyer, 2008;Brown et al, 2008;Jenkins et al, 2011). Forest structure, composition, and disturbance patterns across the vast range of these species were affected by impacts associated with industrialized society: grazing of large herds of introduced livestock (Belsky and Blumenthal, 1997), logging and conversion to even-aged forests (Naficy et al, 2010), and extended fire exclusion starting as early as the mid-19th century (California, Oregon, South Dakota) or beginning as late as the mid-20th century (northern Mexico) (Allen et al, 2002;.…”

Sequentially contingent fires, droughts and pluvials structured a historical dry forest landscape and suggest future contingencies

“…Mixed‐ and high‐severity fires in dry forests were historically infrequent, but were not unprecedented or precluded post‐fire tree recruitment (this study; Sherriff & Veblen ; Frechette & Meyer ; Jenkins et al. ; Williams & Baker , ). Furthermore, our data and those of others suggest tree recruitment historically could lag for decades after drought (Bigler et al.…”

“…Frechette & Meyer ; Jenkins et al. ) suggest that even given future fire and climatic variability, tree recruitment, possibly at elevated levels could succeed in dry forests, as it has for centuries and millennia, or it could fail, depending on the duration, timing and order of events over several decades after these events.…”

“…Frechette & Meyer ; Jenkins et al. ; Williams & Baker , ). Mixed‐severity fires foster multi‐aged forests with patches of even‐aged, post‐fire cohorts (Heyerdahl ; Taylor & Skinner ; Bigio ).…”

Setting the Stage for Mixed- and High-Severity Fire

“…Paleoecologists have explored fire-induced sediment layers in alluvial fans (e.g., Pierce et al, 2004) and charcoal sediments (e.g., Whitlock et al, 2008;Colombaroli and Gavin, 2010;Jenkins et al, 2011;Marlon et al, 2012) to reconstruct historical fire occurrence. They found numerous periods of large and severe fire activity over the past several centuries and millennia in North American mixed-conifer and ponderosa pine forests (see Chapter 9 for many additional citations).…”