Long-Term Post-Wildfire Dynamics of Coarse Woody Debris After Salvage

Forest Ecology and Management 255 (2008) 3952–3961 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco Long-term post-wildfire dynamics of coarse woody debris after salvage logging and implications for soil heating in dry forests of the eastern Cascades, Washington Philip G. Monsanto, James K. Agee * College of Forest Resources, Box 352100, University of Washington, Seattle, WA 98195-2100, USA ARTICLE INFO ABSTRACT Article history: Long-term effects of salvage logging on coarse woody debris were evaluated on four stand-replacing Received 19 December 2007 wildfires ages 1, 11, 17, and 35 years on the Okanogan-Wenatchee National Forest in the eastern Cascades Received in revised form 12 March 2008 of Washington. Total biomass averaged roughly 60 Mg haÀ1 across all sites, although the proportion of Accepted 13 March 2008 logs to snags increased over the chronosequence. Units that had been salvage logged had lower log biomass than unsalvaged units, except for the most recently burned site, where salvaged stands had Keywords: higher log biomass. Mesic aspects had higher log biomass than dry aspects. Post-fire regeneration Salvage logging increased in density over time. In a complementary experiment, soils heating and surrogate-root Soil heating Wildfire mortality caused by burning of logs were measured to assess the potential site damage if fire was Pinus ponderosa reintroduced in these forests. Experimentally burned logs produced lethal surface temperatures (60 8C) Coarse woody debris extending up to 10 cm laterally beyond the logs. Logs burned in late season produced higher surface Washington state temperatures than those burned in early season. Thermocouples buried at depth showed mean maximum temperatures exponentially declined with soil depth. Large logs, decayed logs, and those burned in late season caused higher soil temperatures than small logs, sound logs, and those burned in early season. Small diameter (1.25 cm), live Douglas-fir branch dowels, buried in soil and used as surrogates for small roots, indicated that cambial tissue was damaged to 10 cm depth and to 10 cm distance adjacent to burned logs. When lethal soil temperature zones were projected out to 10 cm from each log, lethal cover ranged up to 24.7% on unsalvaged portions of the oldest fire, almost twice the lethal cover on salvaged portions. Where prescribed fire is introduced to post-wildfire stands aged 20–30 years, effects of root heating from smoldering coarse woody debris will be minimized by burning in spring, at least on mesic sites. There may be some long-term advantages for managers if excessive coarse woody debris loads are reduced early in the post-wildfire period. ß 2008 Elsevier B.V. All rights reserved. 1. Introduction historical dry forests, observations consistent with the frequent recurrence of fire, which would limit the standing life of snags and Prior to European settlement, wildland fire was the major consume logs due to fire recurrence on a near decadal basis historical disturbance factor in seasonally dry forests of the (Skinner, 2002; Agee, 2002). Intermountain West. These low elevation forests, typically Fire exclusion in the 20th century, together with livestock dominated by Pinus ponderosa (ponderosa pine), were maintained grazing and selective removal of large P. ponderosa, changed the by frequent, low intensity fires (Everett et al., 2000; Wright and fuel and vegetation structure of these dry forests. Tree densities Agee, 2004), which consumed fuels, killed small trees, and increased by orders of magnitude, single canopied forests became maintained open forests in classic low-severity fire regimes (Agee, multi-canopied forests, average tree size declined, and dead fuel 1993, 1998; Covington and Moore, 1994; Covington et al., 1994). loads increased (McNeil and Zobel, 1980; Covington et al., 1994). Early travelers described the ease with which horses could be While climate has historically (Heyerdahl et al., 2001) and more galloped through these groves, and the ease with which wagons recently (Westerling et al., 2006) been a driver of fire size, the type traversed these forests (Dutton, 1881; Agee and Maruoka, 1994). of stand-replacing fire that is now commonly observed in these These descriptions imply that coarse woody debris was limited in forests appears to have been nearly absent in historical dry forests based on the density of fire-scarred trees that survived 20–30 fires * Corresponding author. Tel.: +1 425 868 6031; fax: +1 206 543 3254. (Heyerdahl et al., 2001; Wright and Agee, 2004). The increase in E-mail address: [email protected] (J.K. Agee). fire severity, largely due to changes in fuels and stand structure, 0378-1127/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2008.03.048 P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961 3953 was predicted as early as the 1940s (Weaver, 1943). After these higher-severity wildfires, forests that once had sustainable but limited quantities of coarse woody debris now have much to all of the large, live, above-ground biomass converted to coarse woody debris. Post-wildfire removal of the dead timber, a process known as salvage logging, has sometimes been attempted, primarily to recoup economic value. Concern has been raised about damage to ecological values (Beschta et al., 2004; Lindenmayer et al., 2004), and a review of the available literature on salvage logging (McIver and Starr, 2000) found almost all studies dealt with short-term effects, and none, as expected due to the unplanned timing of the wildfires, were experimental in nature. Modeled fire behavior was projected to increase immediately after salvage logging in the Biscuit Fire in southwest Oregon (Donato et al., 2006) due to fine fuels left after tree fall and yarding. Fuel loading projections over longer timeframes (McIver and Ottmar, 2007) after salvage logging in northeastern Oregon with fine woody debris loads almost identical to the Biscuit fire (6.2–6.7 Mg haÀ1 for salvaged stands and 1.3 Mg haÀ1 for unsalvaged stands) suggested that these fine fuel loads would converge over time as fuel mass from unsalvaged stands would differentially increase as the higher number of snags fell in those areas (McIver and Ottmar, 2007). Higher fire severity occurred in 15-year-old stands salvaged logged and planted than in unmanaged stands in areas of the Silver fire (1987) reburned by the Biscuit fire (2002) in southwest Oregon, but the relative influence of fuels and young tree density could not be separated (Thompson et al., 2007). No experimental or retrospective studies have looked at long-term effects of decisions to salvage log severely burned stands in dry forests. For example, if young post-fire stands are actively managed to avoid subsequent stand-replacing events, what is the relative influence of coarse woody debris with and without salvage logging on effects such as soil heating and root mortality from prescribed fire? Fig. 1. Location of the four wildfires analyzed in this study. Approximate center of 0 00 0 00 As forests dominated or co-dominated by P. ponderosa recover study area is located at NAD83 47844 15 N, 120822 08 W. after being burned by high-severity wildfires, the typical dry summer conditions and long fire seasons virtually ensure that (within 199–1697 ha sample units; Everett et al., 2000), in part due future wildfire will occur and place the young post-fire forest stands to the fire climate of the area. Climate is hot and dry during at risk for another stand-replacing event. Active management, such summer months, with mean maximum July temperatures over as prescribed fire, may be desirable to reduce the potential intensity 30 8C and July precipitation less than 1 cm (Entiat Fish Hatchery, and severity of future wildfires. Yet few studies have focused on the 1989–2003 NAD83 4784105400N, 12081902500W, Western Regional dynamics of post-wildfire coarse woody debris in dry forests (see Climate Center, 2003). Annual precipitation averages 34 cm, with a Passovoy and Fule, 2006), and the implications of salvage logging on gradient of increasing precipitation west from the Columbia River. the potential severity of either prescribed fires or subsequent On the driest aspects (south and west) of all four study units, forest wildfires. We saw a significant retrospective opportunity to do this series are P. ponderosa and Pseudotsuga menziesii, and on the higher in eastern Washington, where four large, stand-replacing wildfires productivity mesic aspects (north and east), forest series are P. in dry forest types had periodically occurred over the previous 35 menziesii and a minor amount of Abies grandis (Lillybridge et al., years. We chose to evaluate the following questions: 1995). Fire had been excluded from these areas from 60 to 90 years at the time of each of the stand-replacing wildfires, and some areas What are the patterns of coarse woody debris mass and cover up experienced selective harvest of old-growth ponderosa pine. to 35 years after wildfire in the presence and absence of salvage logging? 2.2. Coarse woody debris study design and methods What are the patterns of soil heating and fine root mortality caused by experimentally burning logs? Each of the four wildfires burned for weeks to months through a variety of fire weather conditions, and after each fire, timber was 2. Methods salvaged on a portion of each burned landscape. We did not have records to establish either the exact locations of salvage or the 2.1. Study area intensity of salvage on any of the fires except for the Fischer Fire. We could identify salvaged stands by searching for charcoal-free Four dry forest study units that burned with high-severity fire cut surfaces of stumps, and unsalvaged stands by the presence of in the Wenatchee River and Entiat River basins of the Okanogan- either large snags or logs associated with each stub or stump.

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