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and Management 255 (2008) 3952–3961

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Forest Ecology and Management

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Long-term post-wildfire dynamics of after salvage and implications for heating in dry 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 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 averaged roughly 60 Mg ha1 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, heating and surrogate-root Soil heating Wildfire mortality caused by burning of logs were measured to assess the potential site damage if fire was 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 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 and structure of these dry forests. densities Agee, 2004), which consumed , killed small , 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 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 / 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 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 ha1 for salvaged stands and 1.3 Mg ha1 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 -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. The Wenatchee National Forest (Fig. 1) were selected for study: the range of salvage intensity was similar on each fire, but the average 2004, 6700 ha Fischer Fire (1 year); 1994, 38,000 ha Tyee Fire (11 volume removed likely differed, with higher average salvage years); 1988, 21,000 ha Dinkelman Fire (17 years); and 1970, intensities on the older fires due to less attention to the retention of 25,000 ha Entiat Fire (35 years). Historical (1700–1900 A.D.) fire dead for wildlife purposes. Due to the difference in frequency at Mud Creek within the Tyee fire area averaged 7 years productivity between dry (south, west) and mesic (north, east) 3954 P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961

Fig. 2. (A) The placement of thermocouples adjacent to and beneath logs. Thermocouples X1–X5 are located at 10 cm from log edge, log edge, center of log, log edge, and 10 cm from log edge. Thermocouples X3 and X6–X8 are located at 0, 5, 10, and 15 cm depth beneath log center. (B) The root surrogates of Douglas-fir branch dowels are located at 0, 5 and 10 cm beneath the log center and at 5 and 10 cm depth at 10 cm away from the log edge. aspects, we assumed that coarse woody debris might differ by which was a loamy, mixed, shallow, Vitrandic Haploxeroll (NRCS, aspect, and therefore stratified our sampling by aspect. The limited 2007). Large rocks were removed from the mostly inorganic soil, areas that reburned between any two fires were identified from and soil was packed to a depth of 40 cm in each deck. Forty logs, mapped perimeters and avoided for sampling. each 1.2 m in length, were burned over the 2006 fire season (early The experimental design was a stratified randomized sampling [6/21–7/21] and late [9/1–10/1]), in two diameter classes (20 cm design. Sample units were distributed evenly across the following and 40 cm) and two decay classes (sound: bark intact and wood factors: Fire Unit (4 wildfires of ages 1, 11, 17, and 35), Salvage (2; showing little obvious decay; and rotten: little bark and evidence present or absent), and Aspect (2; dry or mesic). Each factor of cubical rot). combination was represented by three sampling units, for a total Each log was weighed using a hanging scale before and after sample size of 48 sites. While we recognized that fire unit can be burning to determine consumption. The log was placed on a bed of considered a pseudoreplicated factor, the large size of the units and pine needles and fine branches and ignited once from each edge of the length of time they burned (weeks to months) made each fire the log deck. Log decks were instrumented with eight type K unit quite variable within itself. thermocouples (Fig. 2a) with four directly beneath the log (0, 5, 10, At each randomly selected sample location, a center point was and 15 cm depths), and five at the surface (center of log, one at each established and plots and transects were used to measure coarse edge of the log, and one 10 cm from each edge of the log). woody debris (snags and logs) and post-fire vegetation. Variable- Thermocouples were connected to a CR1000 datalogger (Campbell radius plots with a 5 BAF (English unit) prism and 10 m 10 m Scientific, North Logan, UT, USA) that recorded temperature every fixed plots were established at the sample point center and at two second for a per-minute average. Temperatures above 60 8C were locations 50 m from the center, with the direction of the first line of particular importance, as that threshold for one minute or longer located randomly, and the second also located randomly, subject to has been associated with tissue death (Hare, 1961). the constraint that the angle between the two lines exceeded 908. A more direct evaluation of lethal heat was obtained by The variable-radius plots were used to measure live and dead tree burying short dowels of live Douglas-fir branches around the logs composition, structure and density. Each live ‘‘in’’ tree had the as surrogates for fine roots. The dowels were freshly cut segments following characteristics measured: species, height, diameter at of branches, about 10 cm long, and 1.25 cm in diameter. Six breast height (dbh), crown ratio, dominance, and whether or not it dowels were used for each of 36 logs: one control, three buried was a post-fire surviving residual. Snags had species, dbh, broken directly under the log at 0, 5, and 10 cm depths, and two buried top diameter, and decay class (Maser et al., 1979) recorded. Small 10 cm away from the log edge at 5 and 10 cm depths (Fig. 2b). After trees with no dbh were tallied by species on the 10 m 10 m plot. each log was burned, the dowels were removed and refrigerated The two 50 m lines were used to measure log biomass and cover overnight with the control. The next morning an orthotolodiene- (Brown, 1974; Bate et al., 2004). Log cover was measured using urea hydroxide solution was applied to exposed cambial tissue on model II of Bate et al. (2004): each dowel to assess tissue condition: if the rusty red color turned dark blue after application, the tissue remained alive (Ryan et al., p hiX percent cover ¼ d 1988). Each dowel was then classified as live or dead. 2L i where L = length of sample line and d = diameter of log at 2.4. Data analysis intersection with line. Only dead fuels exceeding 7.62 cm at the point of intersection Coarse woody debris was evaluated based on changes in (lower threshold of 1000-h timelag fuels) were measured. biomass, log biomass and cover, and the proportion of log biomass in rotten versus sound logs. Snag biomass (boles only, branches 2.3. Log burning study design and methods were ignored) was calculated using an estimate of log volume by Smalian’s rule (Bell and Dilworth, 2002). Specific gravities of 0.48 Log segments were experimentally burned on 1.25 m 1.85 m for sound logs and 0.30 for rotten logs (Lolley, 2005) were applied decks constructed of cement block frames filled with local soil, to the data to compute mass. Log biomass and cover were P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961 3955 computed for each transect using standard methods for estimating fuel loads (Brown, 1974; Bate et al., 2004) and averaged by site. The proportion of biomass and cover in rotten logs was calculated for each line averaged by site, and transformed with an arcsine function (Zar, 1999) to normalize the distribution of model residuals. Live tree data were used to calculate post-fire stand density, but because current density is an unknown mix of planting and natural regeneration it is not quantitatively analyzed. Analysis of variance was used to evaluate the effects of time since fire, aspect, and post-fire logging history on coarse woody debris. Fire unit (time since fire) aspect, and logging history were all treated as fixed treatment effects in three-way ANOVA analyses for log biomass and cover. Analysis of total coarse woody debris biomass was done only for unsalvaged stands in order to assess natural of the entire coarse dead wood biomass over time. A two-way fixed effects ANOVA with fire unit and aspect as factors was applied to these data. The proportion of biomass and cover in rotten logs, transformed with an arcsine (Zar, Fig. 3. Total coarse woody debris on unsalvaged portions of the four sites. On the x- 1999) was analyzed using a one-way ANOVA, with the fixed effect axis, the first letter refers to site (F = Fischer (1 year), T = Tyee (11 years), of fire unit. D = Dinkelman (17 years), and E = Entiat (35 years), and the second letter refers to Mean maximum temperatures recorded in the log burning aspect (D = Dry, M = Mesic). experiment were analyzed using two four-way fixed effects ANOVAs with treatments thermocouple location, diameter class, 3.2. Timber salvage effect on log biomass and cover decay class, and season of burn. The first analysis was conducted on the surface thermocouples (Fig. 2a) and the second was conducted Log biomass increased with time since fire (P = .000), as snags on the thermocouples buried at depth. An unbalanced design decayed and fell (Fig. 3). Salvage significantly reduced log biomass resulted from occasional malfunction of a thermocouple, so the (P = .000), and all interactions were also significant (.000 < P < results utilized a conservative Type III sums of squares. .039). Log biomass ranged from 0.1 Mg ha1 (SE = 0.04) on Fischer The root surrogate dowels were analyzed using three Chi- (1 year) mesic unsalvaged stands to 55.3 Mg ha1 (SE = 7.1) in square tests. The first analysis included those dowels buried Entiat (35 years) mesic unsalvaged stands (Fig. 4). The salva- directly beneath the log (Fig. 2b), and as these data were ge unit interaction (P = .000) was due to the Fischer (1 year) fire frequencies of live or dead dowels, a Chi-square test was used having more log biomass on salvaged units, whereas all the other on a 2 3 contingency table (live or dead, three depths). The units showed a decrease in log biomass on salvaged units. There second and third analyses consisted of 2 2 contingency tables was less log biomass on dry aspects than on mesic aspects using surrogate root condition (live or dead), and under and (P = .002), and again the Dinkelman (17 years) unit showed a larger adjacent to the log (log center or 10 cm from edge of log) in order to effect of aspect than other units (including Fischer, as there was test the effect of distance from log on tissue survival. Separate very little log biomass there on either aspect group). analyses were conducted on surrogate roots buried at 5 cm depth The cover of logs followed similar trends to log biomass, as the and 10 cm depth. metrics are related. Cover varied from 0% on Fischer (1 year) mesic Significant effects were evaluated on the basis of P-values of unsalvaged stands to 10.2% on the Entiat (35 years) mesic 0.05 or lower.

3. Results

3.1. Total coarse woody debris

In the absence of salvage logging, total coarse woody debris averaged about 60 Mg ha1 but varied by fire unit (P = .001), aspect (P = .000), and the fire unit x aspect interaction (P = .001) (Fig. 3). There was not a linear change with time, as the Dinkelman unit (17 years fire) had the lowest average mass. Mesic aspects had a higher total biomass than dry aspects, and the effect of aspect varied by unit. On two units (Tyee [11 years] and Entiat [35 years]) total biomass was similar on both aspects, but on the Dinkelman and Fischer units, total biomass on dry aspects was less than on mesic aspects. These two units are furthest east and slightly drier than the other two units, so the effect of aspect might be magnified on these units. After 35 years, the total biomass appears not to have significantly changed in a clear temporal pattern, although the proportion of standing versus down and sound versus rotten have Fig. 4. Effect of timber salvage on log biomass. Dry and mesic aspects are averaged changed. The proportion of the total biomass in snags declines with together on each site. The box represents the interquartile range which contains the time, and the proportion of the log biomass that is rotten increases middle 50% of records. The upper edge of boxes indicates the 75th percentile, and the lower edge indicates the 25th percentile. The line in the box indicates the from close to zero on the 1 year (Fischer) and 11 years (Tyee) fires median value. Whiskers indicate minimum and maximum data values. The asterisk to 7% on the 17 years (Dinkelman) fire and 57% on the 35 years indicates a high outlier in the dataset on a no-salvage, dry aspect sample that was (Entiat) fire (P = .001). close to a clump of top-snapped trees. 3956 P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961

Table 1 Table 2 Comparison of (A) mean log percent cover (standard error in parentheses) and (B) Post-fire density (ha1) of live trees with measurable diameter at breast height effective range of lethal cover when 20 cm are added to each log (dbh), trees shorter than breast height, and total trees (standard error)

Fischer (1) Tyee (11) Dinkelman (17) Entiat (35) Year (fire) Salvage No salvage

A. Dry Mesic Dry Mesic Dry unsalvage 0.3 (.13) 5.6 (.09) 2.9 (.20) 6.4 (.47) Dry salvage 0.3 (.09) 3.0 (.64) 1.2 (.26) 4.8 (1.00) Trees with dbh Mesic unsalvage 0.0 (.00) 6.1 (.34) 8.4 (1.03) 10.2 (.87) 1 (Fischer) 2.9 (0.1) 5.7 (0.2) 12.1 (0.3) 5.4 (0.2) Mesic salvage 2.5 (.26) 5.3 (.64) 6.4 (.77) 4.9 (.59) 11 (Tyee) 0.0 (0.0) 125.9 (3.5) 4.6 (0.1) 0.0 (0.0) 17 (Dinkelman) 78.9 (2.2) 70.7 (2.0) .1 (0.0) 79.7 (2.2) B. 35 (Entiat) 1069.2 (30.1) 1073.4 (30.2) 478.6 (13.5) 2269.5 (63.9) Dry unsalvage 0.6 (.22) 11.3 (.09) 6.4 (.51) 12.9 (.62) Dry salvage 0.7 (.21) 7.3 (1.60) 2.9 (.37) 11.0 (2.12) Trees with no dbh Mesic unsalvage 0.1 (.04) 15.8 (.70) 21.1 (2.94) 24.7 (2.22) 1 (Fischer) 7 (4.6) 126 (33.3) 53 (23.1) 7 (6.6) Mesic salvage 6.2 (.55) 13.6 (1.71) 15.8 (1.49) 11.4 (1.51) 11 (Tyee) 136 (24.8) 375 (49.6) 355 (117.0) 359 (37.5) 17 (Dinkelman) 110 (54.4) 249 (45.5) 10 (5.6) 60 (18.1) 35 (Entiat) 608 (64.0) 575 (99.5) 515 (117.8) 1498 (347.5) unsalvaged sites (Table 1A). The only difference in the cover Total trees analysis was the absence of the salvage x aspect interaction 1 (Fischer) 9.9 131.7 65.1 12.4 11 (Tyee) 136 500.9 359.6 359 (P = .930) in the log cover analysis. All main effects and the other 17 (Dinkelman) 188.9 319.7 10.1 139.7 two-way interactions had P = .000, and the three-way interaction 35 (Entiat) 1677.2 1648.4 993.6 3767.5 was significant at P = .003. Year indicates age of fire referenced to 2005.

3.3. Young stand recovery (Table 2). Regeneration was almost exclusively P. ponderosa and P. The young recovering stands on all units were likely a mix of menziesii. On the Entiat fire, was a codominant natural regeneration and planting, and the two sources of origin species, and the average density was over 1200 stems ha1. Total could not be separated. There was a low density of regeneration tree density, including trees below breast height, suggest adequate with measurable breast-high diameter, averaging less than to overstocked conditions in post-fire years 11–35 on all but the 100 stems ha1, on all units except for the Entiat (35 years) fire dry aspects of the Dinkelman (11 years) site.

Fig. 5. Temperature profiles for small diameter logs (20 cm) (a) burned late spring/early summer and (b) burned late summer/early fall. Lines represent average of replicates for each treatment. Adjoining graphs, from left to right, represent 10 cm from left edge of log (10L), left edge of log (L), directly beneath center of log (C), right edge of log (R), and 10 cm from right edge of log (10R). P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961 3957

3.4. Temperature profiles around logs temperatures to 15 cm depth, but small logs, regardless of decay class, reached lethal temperatures only down to 5 cm. Moisture content of small and large diameter logs averaged 17.7 and 14.7% in early season to 11.9 and 12.5% in late season. Log 3.5. Effects of soil heating on root surrogates consumption increased from 52 and 59.2% consumption in early season to 70.8 and 74.3% in late season burns. Soil moisture was Mean bark thickness of the Douglas-fir live branch dowels used equivalent to air-dry conditions (<5%). Mean maximum surface as root surrogates was 1.2 mm (S.D. 0.4 mm). All control dowels, temperatures spiked early in the flaming period for both small cut at the same time as treatment dowels and refrigerated diameter (Fig. 5) and large diameter (Fig. 6) logs, and gradually overnight with them, showed no cambial damage when measured decreased as more smoldering occurred. In all the next day. In most treatment combinations, a majority of the conditions, mean maximum surface temperatures were well dowels showed signs of cambial damage (Table 3). Directly above lethal temperatures for cambial tissue. Mean maximum beneath logs, 83 of 108 surrogate roots had dead tissue (Table 4). surface temperatures for diameter class (P = .504), decay class There were no differences in the frequency of mortality with depth (P = .065), and thermocouple location (P = .057) did not differ. directly under the log (Table 3a; x2 = 3.85, x2 critical = 5.99). There Lethal temperatures were reached out to 10 cm distance from were also no differences between the frequency of mortality each log edge. Logs burned in late season, however, did show between dowels buried at 5 cm depth and 10 cm depth between higher surface temperatures than those burned in early season locations directly under the log and at 10 cm distance from the (P = .000). edge of the log(x2 values of 0.84 and 3.65 compared to x2 critical Thermocouples buried at depth under small diameter (Fig. 7) value of 3.84). and large diameter (Fig. 8) logs showed more differences. There were differences in mean maximum temperatures due to depth 3.6. Lethal zone of cover from burning logs (P = .000), diameter class (P = .001), decay class (P = .043), and season (P = .006), with a diameter season interaction (P = .005). Given the results of the root surrogate treatment, the lethal Mean maximum temperature decreased with depth (Fig. 9), and zone for roots, even those not right at the surface, extended a lethal temperatures were reached on all early season logs to 5 cm minimum of 10 cm away from each edge of the burning log. depth but not deeper. Large logs, rotten logs, and late season burns Therefore, an additional 20 cm was added to each log diameter had higher temperatures than small logs, sound logs, and early measured on the log transects on the four study units, and an season burns. Large logs burned in late season reached lethal estimate of lethal cover was calculated (Table 1B). The highest

Fig. 6. Temperature profiles for large diameter logs (40 cm) (a) burned late spring/early summer and (b) burned late summer/early fall. Lines represent average of replicates for each treatment. Adjoining graphs, from left to right, represent 10 cm from left edge of log (10L), left edge of log (L), directly beneath center of log (C), right edge of log (R), and 10 cm from right edge of log (10R). 3958 P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961

Fig. 7. Temperature profiles for small diameter logs (20 cm) (a) burned late spring/early summer and (b) burned late summer/early fall. Lines represent average of replicates for each treatment. Adjoining graphs, from left to right, represent 0, 5, 10, and 15 cm in the soil.

Fig. 8. Temperature profiles for large diameter logs (40 cm) (a) burned late spring/early summer and (b) burned late summer/early fall. Lines represent average of replicates for each treatment. Adjoining graphs, from left to right, represent 0, 5, 10, and 15 cm in the soil. P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961 3959

Table 4 Contingency tables for surrogate roots in various configurations around and beneath logs

Depth (cm)

0 5 10 Total

A. A 2 3 contingency table for surrogate roots directly beneath logs Live 5 8 12 25 Dead 31 28 24 83

Total 36 36 36 108

Location at 5 cm depth

Log center 10 cm from edge Total

B. A 2 2 contingency table for surrogate roots buried at 5 cm depth directly under the log and at 10 cm distance from the edge of the log Live 8 5 13 Dead 28 31 59

Total 36 36 72 Fig. 9. Maximum temperatures (8C) reached from the surface to 15 cm depth directly under burning logs. Location at 10 cm depth actual cover of logs was 10.2% on the 35-year-old unit (mesic Log center 10 cm from edge Total unsalvaged at Entiat), and this increased to a lethal cover up to C. A 2 2 contingency table for surrogate roots buried at 10 cm depth directly 24.7% when the additional lethal heating zone was added. Salvaged under the log and at 10 cm distance from the edge of the log sites within the Entiat unit averaged about 12% lethal cover, with Live 11 19 30 Dead 25 17 42 little difference between aspects. Total 36 36 72 4. Discussion

Stand-replacing fires, while historically uncommon in dry mean percent cover of logs, by post-wildfire age 35, ranged from forests of the American West, were historically the norm in wet 4.8 to 10.2% 35 years after wildfire (Table 1), much higher than in and/or cold forests (Romme, 1982; Agee, 1993). ‘‘Boom and bust’’ old growth stands of dry forests and at levels higher than suggested patterns, beginning with large increments of coarse woody debris to optimize protection of soils and wildlife while mitigating immediately after the fire, followed by decreases due to decom- fire danger (Brown et al., 2003). position and lack of new input from the young, small post-fire These fire-prone environments are dry enough that natural trees, and eventual increases when the new forest produced trees decomposition is slow. Using Olson’s (1963) single exponential large enough to persist as logs, created a U-shaped distribution of decay model and the decay rate constant of 0.073 for P. ponderosa coarse woody debris over centuries (Harmon et al., 1986; Agee and (>25 cm) (Harmon et al., 1986), snag bole fragmentation could Huff, 1987). Much lower and less variable coarse woody debris take more than 40 years, and this rate appears to close to what we patterns were characteristic of historic P. ponderosa forests (Agee, observed at the 35-year-old Entiat fire (Fig. 3). However, this 2002). With the change in fire regime from low-severity to mixed- process was nearly the same on the 11-year-old Tyee fire, so that or high-severity, seasonally dry forests being burned now by local factors likely create substantial variability on the conversion intense fires have biomass and cover of coarse woody debris at of snags to down logs. Parminter (2002) estimated a decay rate for many times historical levels (Agee, 2002; Skinner, 2002). For log boles of 0.035, and McIver and Ottmar (2007) used 0.03 and example, cover of logs in old-growth P. ponderosa stands of central 0.02 for P. ponderosa and P. menziesii logs. These rates would result Oregon and northern was 1.7% (Youngblood et al., 2004), in 100–150 years for a population of logs to decompose. During and a study in old growth Pinus jeffreyi forest in Mexico calculated a that time, the stands remain at risk to wildfire. Early in succession log cover of 1.5% (Stephens et al., 2007). Ohmann and Waddell (ages 0–30) the young trees are small enough that regardless of (2002) estimated percent cover of logs between 12 and 50 cm coarse woody debris loads, high-severity fire is likely to occur if diameter in young, mature, and old-growth forests to be 1.1, 1.3, another wildfire burns through the stand (McIver and Ottmar, and 1.0% for P. ponderosa forests of Oregon and Washington. Our 2007; Thompson et al., 2007).

Table 3 Percent of P. menziesii surrogate roots showing cambium death as indicated by Orthotolidiene/urea hydroxide solution

Log size, decay, and season burned Surface 5 cm depth 5 cm depth (10 cm edge) 10 cm depth 10 cm depth (10 cm edge)

Large diameter logs Early rotten 100 75 75 50 50 Early sound 33 33 100 33 0 Late rotten 100 100 100 100 100 Late sound 80 80 80 80 80

Small diameter logs Early rotten 100 80 80 60 0 Early sound 75 75 75 50 25 Late rotten 100 80 100 80 60 Late sound 100 80 80 80 40

‘‘10 cm edge’’ refers to dowels 10 cm from the edge of logs. 3960 P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961

While our results were restricted to coarse woody debris, they residues up to 12.5 cm deep created lethal surface temperatures are consistent with what Donato et al. (2006) and McIver and that increased with soil dryness and mulch depth. Lethal Ottmar (2007) found with fine woody debris: salvage logging temperatures were observed down to 10 cm depth in the heavier immediately increases the biomass of woody debris on the ground. mulch treatment, and they suggested burning these residues At the Fischer fire, this biomass consisted of lopped and scattered ranked between moderate severity prescribed fires and damaging tops left after the salvage logging. The convergence of levels of fine effects of heavy slash fires. The spatial distribution of wood mulch woody debris between salvaged and unsalvaged stands suggested at one site showed that about 25% of the area would experience by McIver and Ottmar (2007) occurred in our study with coarse lethal temperatures to 10 cm depth, but at another site the mulch woody debris. By age 10, levels of coarse woody debris in salvaged depths were less and lower soil heating would be predicted there. stands fell below those of unsalvaged stands, and that pattern Whether stands have been salvaged or not, soil heating from remained through age 35. Salvage removes boles that would smoldering logs will be a concern. Salvage reduces but does not otherwise become coarse woody debris, so one would expect eliminate coarse woody debris. Some coarse woody debris will be lowered coarse woody debris levels decades after salvage logging valuable for wildlife habitat (Brown et al., 2003), and some will be compared to unsalvaged sites. too small to be commercially useful. Spring burning may be one The difference in percent cover of coarse woody debris between solution where high levels of coarse woody debris occur. Our data salvaged and unsalvaged stands at the 35-year-old Entiat fire suggest that spring burns had less heating than fall burns, and early ranged from 1.6 (dry aspects) to 5.3% (mesic aspects). When the season burns typically cover less area. If we had used moist soil lethal cover was calculated, these differences increased to 1.9 (dry under the logs burned in late spring, the differences likely would aspects) to 13.3% (mesic aspects), and almost 25% lethal cover have been even more pronounced (Frandsen and Ryan, 1986). occurred on unsalvaged mesic aspects at the Entiat fire. These Perrakis and Agee (2006) reported for old-growth forest a range of values suggest that prescribed fire introduced for the purpose of 19–37% area burned from spring burns with a much higher 64–86% lowering wildfire risk could significantly damage young stands, for fall burns. Spring burns typically consume less coarse woody even if crown damage was minimal, due to root damage, as has debris, too. Knapp et al. (2005) reported 57% of log biomass been demonstrated for old growth pine stands (Swezy and Agee, consumed in spring burns compared to 83% in fall burns, again in 1991; Kolb et al., 2007). On dry aspects, which might be chosen as a old-growth forest. Spring prescribed burns in the 1970 Entiat fire, higher priority for young stand fuel treatments, salvage appeared under young stands, showed similar patchiness (Peterson et al., to have a less dramatic effect than on the mesic aspects. 2007). All of the forest floor was consumed over 45% of the area, We used live Douglas-fir branches as surrogates for small roots between 5 and 95% was consumed on 27% of the area, and 28% of (1.25 cm and smaller). We justified this on the basis that in situ the area was unburned. It would seem prudent that for mesic experiments were not easily designed, and that small branches aspects in unsalvaged areas, initial prescribed burns in spring should function similarly to roots in a physiological sense. Our would be favored to mitigate the effect of root heating from controls indicated that a cut branch left out for the day and smoldering logs. Subsequent fires in such areas, and initial fires in refrigerated overnight showed no cambial damage the next day. salvaged stands, might have wider seasonal windows for burning. We were confident that the root surrogate treatment would be a In the past, most concerns regarding salvage logging have dealt better test of root damage than temperature profiles alone, and the with short-term issues (Beschta et al., 2004). Longer-term results suggested substantial damage could occur to roots not only ecological effects, such as some of the effects of excessively high beneath burning logs but also adjacent to them. Our tests were levels of coarse woody debris, should be factored into the decision- conservative, as we used a single log model. When large woody making process. In dry forest types there may be some long-term fuels burn in isolation, as in our experiments, they may burn with advantages for managers if excessive coarse woody debris loads less intensity or less completely than when burned in close are reduced early in the post-wildfire period. proximity to other sufficiently dry fuels of the same size or smaller (Albini and Reinhardt, 1995, 1997). Harrington (1981) observed Acknowledgements that grouped logs burned more completely than when they burned in isolation. Therefore, the temperature profiles we measured are This research was funded under Joint Venture Agreement PNW likely conservative, as we only burned single logs. We did not #03-JV-11261927-534, CROP Forest Ecology, between the USDA extend our measurement zone beyond 10 cm from the edge of logs, Forest Service, Pacific Northwest Research Station and the so we did not extrapolate potential damage further away from the University of Washington. Logistical support was provided by burned logs. the Okanogan-Wenatchee National Forest and Wenatchee Sciences Laboratory. D.W. Peterson graciously loaned us the 4.1. Management considerations temperature dataloggers. Field work was provided by R. Wiede- mer, C. Raynham, and D. Anderson. Reviews of an earlier draft were Some managers have considered breaking the cycle of stand graciously provided by M. Busse, D.W. Peterson, M. Dahlgreen, and replacement burning (e.g., Thompson et al., 2007) by intervening J. McIver. with treatments such as prescribed fire when the post-wildfire stand reaches age 20 or 30 (Peterson et al., 2007). By managing tree density and fuels, the intent is to ease the process of fire References suppression should a wildfire occur, create adequate space for Agee, J.K., 1993. Fire Ecology of Pacific Northwest Forests. Island Press, Washington, tree growth, and reduce potential wildfire severity in the young DC. stand. Conducting prescribed fires in young stands with sub- Agee, J.K., 1998. The landscape ecology of western forest fire regimes. Northw. Sci. stantial coarse woody debris presents several challenges, including 72, 24–34. Agee, J.K., 2002. Fire as a coarse filter for snags and logs. In: Laudenslayer Jr., W.F., the amount of from smoldering logs (Hardy et al., 2001). But Shea, P.J., Valentine, B.E., Weatherspoon, C.P., Lisle, T.E. 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