A comparison and integration of tree-ring and alluvial records of fire history at the Missionary Ridge Fire, Durango, Colorado, USA

Abstract

We used tree-ring and alluvial sediment methods to reconstruct past fire regimes for a mixed conifer forest within a 1 km2 drainage basin which was severely burned by a wildfire near Durango, Colorado. Post-fire debris flow events incised the valley-filling alluvial sediments in the lower basin, and created exposures of fire-related of deposits of late-Holocene age. Tree-ring and alluvial sediment fire history records were created separately, and then compared and integrated to create a ~ 3000 year record of past fire activity. The tree-ring record showed that from AD 1679 to 1879, there were frequent surface fires, while patches of high-severity fire occurred during widespread fire years. The alluvial record showed that a low- to moderate-and mixed-severity fire regime has likely been dominant over the past ~ 2600 calibrated calendar years before present, as shown by locally episodic deposition of charcoal-rich, fine-grained sediments. Radiocarbon dating suggested that in two stratigraphic sections, there was rapid deposition of several fine-grained sediment layers. One of these episodes occurred during the Medieval Climatic Anomaly (AD 900—1300). A charcoal-rich debris flow deposit in the oldest exposed part of the stratigraphic record dated to ~ 2600 calibrated calendar years before present. This event was potentially equivalent in magnitude to the debris-flow events following the recent wildfire in the study area, and is evidence of a high-severity fire that burned a large proportion of the study basin. The timing of this event coincides with a period of less frequent, yet more severe wildfires in a nearby lake sediment record, and is associated with the end of a Neoglacial period of cooler and wetter temperatures.

Partitioned by process: Measuring post‐fire debris‐flow and rill erosion with Structure from Motion photogrammetry

“…The majority of post-fire studies have temporal scopes restricted to the present or a few decades prior, and limited work has been done on post-fire erosion over Holocene and Quaternary timescales (Moody et al, 2013;Murphy et al, 2018). A handful of studies investigate erosion and sedimentation responses to wildfire driven by Holocene climate changes by dating charcoal fragments from alluvial fans (Meyer and Pierce, 2003;Pierce et al, 2004Pierce et al, , 2011Bigio et al, 2010;Nelson and Pierce, 2010;Weppner et al, 2013;Riley et al, 2015;Fitch and Meyer, 2016). Over Quaternary timescales, post-fire erosion is responsible for >90% of landscape denudation since 1.24 Ma at Valles Caldera, New Mexico (Orem and Pelletier, 2016).…”

Forest restoration in a surface fire-dependent ecosystem: An example from a mixed conifer forest, southwestern Colorado, USA

“…These changes should favor ponderosa pine regeneration because litter prevents seeds from imbibing water due to poor contact with moist mineral soil and litter provides habitat for damping-off fungi, which cause seedling wilting and mortality (Farmer, 1997). In addition, direct microsite changes from fire such as scorched needles on blackened mineral soil have been shown to favor ponderosa emergence and establishment (Bonnet et al, 2005). Aspen regeneration in thin/burn treatments increased almost fivefold over pre-treatment levels while aspen regeneration in burn alone treatments did not even double.…”

“…Paleoecological studies in the Southwest (Toney and Anderson, 2006;Allen et al, 2008;Bigio et al, 2010) and other regions with similar vegetation types (Whitlock et al, 2003) have extended the long-term historical fire record to the millennial scale providing further evidence that the absence of fire in the 20th century represents an anomaly in forests where the regular occurrence of low intensity surface burning was previously common.…”

Spatiotemporal fire dynamics in mixed‐conifer and aspen forests in the San Juan Mountains of southwestern Colorado, USA

“…Also, evidence of high-severity fire has been evaluated in largely even-aged, upper montane aspen stands (Margolis et al 2007) and in the charcoal record in debris flow sediments (Bigio et al 2010). However, little effort has been directed toward the more mesic mixed-conifer forests or understanding variation in fire or fire-driven forest dynamics across the steep environmental gradients of this region.…”