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
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 19 December 2007
Received in revised form 12 March 2008
Accepted 13 March 2008
Long-term effects of salvage logging on coarse woody debris were evaluated on four stand-replacing
wildfires ages 1, 11, 17, and 35 years on the Okanogan-Wenatchee National Forest in the eastern Cascades
of Washington. Total biomass averaged roughly 60 Mg ha1 across all sites, although the proportion of
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
higher log biomass. Mesic aspects had higher log biomass than dry aspects. Post-fire regeneration
increased in density over time. In a complementary experiment, soils heating and surrogate-root
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)
extending up to 10 cm laterally beyond the logs. Logs burned in late season produced higher surface
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.
Keywords:
Salvage logging
Soil heating
Wildfire
Pinus ponderosa
Coarse woody debris
Washington state
1. Introduction
Prior to European settlement, wildland fire was the major
historical disturbance factor in seasonally dry forests of the
Intermountain West. These low elevation forests, typically
dominated by Pinus ponderosa (ponderosa pine), were maintained
by frequent, low intensity fires (Everett et al., 2000; Wright and
Agee, 2004), which consumed fuels, killed small trees, and
maintained open forests in classic low-severity fire regimes (Agee,
1993, 1998; Covington and Moore, 1994; Covington et al., 1994).
Early travelers described the ease with which horses could be
galloped through these groves, and the ease with which wagons
traversed these forests (Dutton, 1881; Agee and Maruoka, 1994).
These descriptions imply that coarse woody debris was limited in
* Corresponding author. Tel.: +1 425 868 6031; fax: +1 206 543 3254.
E-mail address: jagee@u.washington.edu (J.K. Agee).
0378-1127/$ – see front matter ß 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.foreco.2008.03.048
historical dry forests, observations consistent with the frequent
recurrence of fire, which would limit the standing life of snags and
consume logs due to fire recurrence on a near decadal basis
(Skinner, 2002; Agee, 2002).
Fire exclusion in the 20th century, together with livestock
grazing and selective removal of large P. ponderosa, changed the
fuel and vegetation structure of these dry forests. Tree densities
increased by orders of magnitude, single canopied forests became
multi-canopied forests, average tree size declined, and dead fuel
loads increased (McNeil and Zobel, 1980; Covington et al., 1994).
While climate has historically (Heyerdahl et al., 2001) and more
recently (Westerling et al., 2006) been a driver of fire size, the type
of stand-replacing fire that is now commonly observed in these
forests appears to have been nearly absent in historical dry forests
based on the density of fire-scarred trees that survived 20–30 fires
(Heyerdahl et al., 2001; Wright and Agee, 2004). The increase in
fire severity, largely due to changes in fuels and stand structure,
P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961
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 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?
As forests dominated or co-dominated by P. ponderosa recover
after being burned by high-severity wildfires, the typical dry
summer conditions and long fire seasons virtually ensure that
future wildfire will occur and place the young post-fire forest stands
at risk for another stand-replacing event. Active management, such
as prescribed fire, may be desirable to reduce the potential intensity
and severity of future wildfires. Yet few studies have focused on the
dynamics of post-wildfire coarse woody debris in dry forests (see
Passovoy and Fule, 2006), and the implications of salvage logging on
the potential severity of either prescribed fires or subsequent
wildfires. We saw a significant retrospective opportunity to do this
in eastern Washington, where four large, stand-replacing wildfires
in dry forest types had periodically occurred over the previous 35
years. We chose to evaluate the following questions:
What are the patterns of coarse woody debris mass and cover up
to 35 years after wildfire in the presence and absence of salvage
logging?
What are the patterns of soil heating and fine root mortality
caused by experimentally burning logs?
2. Methods
2.1. Study area
Four dry forest study units that burned with high-severity fire
in the Wenatchee River and Entiat River basins of the OkanoganWenatchee National Forest (Fig. 1) were selected for study: the
2004, 6700 ha Fischer Fire (1 year); 1994, 38,000 ha Tyee Fire (11
years); 1988, 21,000 ha Dinkelman Fire (17 years); and 1970,
25,000 ha Entiat Fire (35 years). Historical (1700–1900 A.D.) fire
frequency at Mud Creek within the Tyee fire area averaged 7 years
3953
Fig. 1. Location of the four wildfires analyzed in this study. Approximate center of
study area is located at NAD83 478440 1500 N, 1208220 0800 W.
(within 199–1697 ha sample units; Everett et al., 2000), in part due
to the fire climate of the area. Climate is hot and dry during
summer months, with mean maximum July temperatures over
30 8C and July precipitation less than 1 cm (Entiat Fish Hatchery,
1989–2003 NAD83 478410 5400 N, 1208190 2500 W, Western Regional
Climate Center, 2003). Annual precipitation averages 34 cm, with a
gradient of increasing precipitation west from the Columbia River.
On the driest aspects (south and west) of all four study units, forest
series are P. ponderosa and Pseudotsuga menziesii, and on the higher
productivity mesic aspects (north and east), forest series are P.
menziesii and a minor amount of Abies grandis (Lillybridge et al.,
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
experienced selective harvest of old-growth ponderosa pine.
2.2. Coarse woody debris study design and methods
Each of the four wildfires burned for weeks to months through a
variety of fire weather conditions, and after each fire, timber was
salvaged on a portion of each burned landscape. We did not have
records to establish either the exact locations of salvage or the
intensity of salvage on any of the fires except for the Fischer Fire.
We could identify salvaged stands by searching for charcoal-free
cut surfaces of stumps, and unsalvaged stands by the presence of
either large snags or logs associated with each stub or stump. The
range of salvage intensity was similar on each fire, but the average
volume removed likely differed, with higher average salvage
intensities on the older fires due to less attention to the retention of
dead wood for wildlife purposes. Due to the difference in
productivity between dry (south, west) and mesic (north, east)
P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961
3954
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
aspect, and therefore stratified our sampling by aspect. The limited
areas that reburned between any two fires were identified from
mapped perimeters and avoided for sampling.
The experimental design was a stratified randomized sampling
design. Sample units were distributed evenly across the following
factors: Fire Unit (4 wildfires of ages 1, 11, 17, and 35), Salvage (2;
present or absent), and Aspect (2; dry or mesic). Each factor
combination was represented by three sampling units, for a total
sample size of 48 sites. While we recognized that fire unit can be
considered a pseudoreplicated factor, the large size of the units and
the length of time they burned (weeks to months) made each fire
unit quite variable within itself.
At each randomly selected sample location, a center point was
established and plots and transects were used to measure coarse
woody debris (snags and logs) and post-fire vegetation. Variableradius plots with a 5 BAF (English unit) prism and 10 m 10 m
fixed plots were established at the sample point center and at two
locations 50 m from the center, with the direction of the first line
located randomly, and the second also located randomly, subject to
the constraint that the angle between the two lines exceeded 908.
The variable-radius plots were used to measure live and dead tree
composition, structure and density. Each live ‘‘in’’ tree had the
following characteristics measured: species, height, diameter at
breast height (dbh), crown ratio, dominance, and whether or not it
was a post-fire surviving residual. Snags had species, dbh, broken
top diameter, and decay class (Maser et al., 1979) recorded. Small
trees with no dbh were tallied by species on the 10 m 10 m plot.
The two 50 m lines were used to measure log biomass and cover
(Brown, 1974; Bate et al., 2004). Log cover was measured using
model II of Bate et al. (2004):
percent cover ¼
p hX
2L
di
i
where L = length of sample line and d = diameter of log at
intersection with line.
Only dead fuels exceeding 7.62 cm at the point of intersection
(lower threshold of 1000-h timelag fuels) were measured.
2.3. Log burning study design and methods
Log segments were experimentally burned on 1.25 m 1.85 m
decks constructed of cement block frames filled with local soil,
which was a loamy, mixed, shallow, Vitrandic Haploxeroll (NRCS,
2007). Large rocks were removed from the mostly inorganic soil,
and soil was packed to a depth of 40 cm in each deck. Forty logs,
each 1.2 m in length, were burned over the 2006 fire season (early
[6/21–7/21] and late [9/1–10/1]), in two diameter classes (20 cm
and 40 cm) and two decay classes (sound: bark intact and wood
showing little obvious decay; and rotten: little bark and evidence
of cubical rot).
Each log was weighed using a hanging scale before and after
burning to determine consumption. The log was placed on a bed of
pine needles and fine branches and ignited once from each edge of
the log deck. Log decks were instrumented with eight type K
thermocouples (Fig. 2a) with four directly beneath the log (0, 5, 10,
and 15 cm depths), and five at the surface (center of log, one at each
edge of the log, and one 10 cm from each edge of the log).
Thermocouples were connected to a CR1000 datalogger (Campbell
Scientific, North Logan, UT, USA) that recorded temperature every
second for a per-minute average. Temperatures above 60 8C were
of particular importance, as that threshold for one minute or longer
has been associated with tissue death (Hare, 1961).
A more direct evaluation of lethal heat was obtained by
burying short dowels of live Douglas-fir branches around the logs
as surrogates for fine roots. The dowels were freshly cut segments
of branches, about 10 cm long, and 1.25 cm in diameter. Six
dowels were used for each of 36 logs: one control, three buried
directly under the log at 0, 5, and 10 cm depths, and two buried
10 cm away from the log edge at 5 and 10 cm depths (Fig. 2b). After
each log was burned, the dowels were removed and refrigerated
overnight with the control. The next morning an orthotolodieneurea hydroxide solution was applied to exposed cambial tissue on
each dowel to assess tissue condition: if the rusty red color turned
dark blue after application, the tissue remained alive (Ryan et al.,
1988). Each dowel was then classified as live or dead.
2.4. Data analysis
Coarse woody debris was evaluated based on changes in snag
biomass, log biomass and cover, and the proportion of log biomass
in rotten versus sound logs. Snag biomass (boles only, branches
were ignored) was calculated using an estimate of log volume by
Smalian’s rule (Bell and Dilworth, 2002). Specific gravities of 0.48
for sound logs and 0.30 for rotten logs (Lolley, 2005) were applied
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
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 decomposition 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,
1999) was analyzed using a one-way ANOVA, with the fixed effect
of fire unit.
Mean maximum temperatures recorded in the log burning
experiment were analyzed using two four-way fixed effects
ANOVAs with treatments thermocouple location, diameter class,
decay class, and season of burn. The first analysis was conducted on
the surface thermocouples (Fig. 2a) and the second was conducted
on the thermocouples buried at depth. An unbalanced design
resulted from occasional malfunction of a thermocouple, so the
results utilized a conservative Type III sums of squares.
The root surrogate dowels were analyzed using three Chisquare tests. The first analysis included those dowels buried
directly beneath the log (Fig. 2b), and as these data were
frequencies of live or dead dowels, a Chi-square test was used
on a 2 3 contingency table (live or dead, three depths). The
second and third analyses consisted of 2 2 contingency tables
using surrogate root condition (live or dead), and under and
adjacent to the log (log center or 10 cm from edge of log) in order to
test the effect of distance from log on tissue survival. Separate
analyses were conducted on surrogate roots buried at 5 cm depth
and 10 cm depth.
Significant effects were evaluated on the basis of P-values of
0.05 or lower.
3955
Fig. 3. Total coarse woody debris on unsalvaged portions of the four sites. On the xaxis, the first letter refers to site (F = Fischer (1 year), T = Tyee (11 years),
D = Dinkelman (17 years), and E = Entiat (35 years), and the second letter refers to
aspect (D = Dry, M = Mesic).
3.2. Timber salvage effect on log biomass and cover
Log biomass increased with time since fire (P = .000), as snags
decayed and fell (Fig. 3). Salvage significantly reduced log biomass
(P = .000), and all interactions were also significant (.000 < P <
.039). Log biomass ranged from 0.1 Mg ha1 (SE = 0.04) on Fischer
(1 year) mesic unsalvaged stands to 55.3 Mg ha1 (SE = 7.1) in
Entiat (35 years) mesic unsalvaged stands (Fig. 4). The salvage unit interaction (P = .000) was due to the Fischer (1 year) fire
having more log biomass on salvaged units, whereas all the other
units showed a decrease in log biomass on salvaged units. There
was less log biomass on dry aspects than on mesic aspects
(P = .002), and again the Dinkelman (17 years) unit showed a larger
effect of aspect than other units (including Fischer, as there was
very little log biomass there on either aspect group).
The cover of logs followed similar trends to log biomass, as the
metrics are related. Cover varied from 0% on Fischer (1 year) mesic
unsalvaged stands to 10.2% on the Entiat (35 years) mesic
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
changed. The proportion of the total biomass in snags declines with
time, and the proportion of the log biomass that is rotten increases
from close to zero on the 1 year (Fischer) and 11 years (Tyee) fires
to 7% on the 17 years (Dinkelman) fire and 57% on the 35 years
(Entiat) fire (P = .001).
Fig. 4. Effect of timber salvage on log biomass. Dry and mesic aspects are averaged
together on each site. The box represents the interquartile range which contains the
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
median value. Whiskers indicate minimum and maximum data values. The asterisk
indicates a high outlier in the dataset on a no-salvage, dry aspect sample that was
close to a clump of top-snapped trees.
P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961
3956
Table 1
Comparison of (A) mean log percent cover (standard error in parentheses) and (B)
effective range of lethal cover when 20 cm are added to each log
Fischer (1)
Tyee (11)
Dinkelman (17)
Entiat (35)
Table 2
Post-fire density (ha1) of live trees with measurable diameter at breast height
(dbh), trees shorter than breast height, and total trees (standard error)
Year (fire)
A.
Salvage
No salvage
Dry
Dry unsalvage
Dry salvage
Mesic unsalvage
Mesic salvage
0.3
0.3
0.0
2.5
(.13)
(.09)
(.00)
(.26)
5.6
3.0
6.1
5.3
Dry unsalvage
Dry salvage
Mesic unsalvage
Mesic salvage
0.6
0.7
0.1
6.2
(.22)
(.21)
(.04)
(.55)
11.3
7.3
15.8
13.6
(.09)
(.64)
(.34)
(.64)
2.9
1.2
8.4
6.4
(.20)
(.26)
(1.03)
(.77)
6.4
4.8
10.2
4.9
(.47)
(1.00)
(.87)
(.59)
6.4
2.9
21.1
15.8
(.51)
(.37)
(2.94)
(1.49)
12.9
11.0
24.7
11.4
(.62)
(2.12)
(2.22)
(1.51)
B.
(.09)
(1.60)
(.70)
(1.71)
unsalvaged sites (Table 1A). The only difference in the cover
analysis was the absence of the salvage x aspect interaction
(P = .930) in the log cover analysis. All main effects and the other
two-way interactions had P = .000, and the three-way interaction
was significant at P = .003.
Mesic
Trees with dbh
1 (Fischer)
11 (Tyee)
17 (Dinkelman)
35 (Entiat)
2.9
0.0
78.9
1069.2
Trees with no dbh
1 (Fischer)
11 (Tyee)
17 (Dinkelman)
35 (Entiat)
7
136
110
608
Total trees
1 (Fischer)
11 (Tyee)
17 (Dinkelman)
35 (Entiat)
9.9
136
188.9
1677.2
(0.1)
(0.0)
(2.2)
(30.1)
(4.6)
(24.8)
(54.4)
(64.0)
5.7
125.9
70.7
1073.4
126
375
249
575
Dry
(0.2)
(3.5)
(2.0)
(30.2)
(33.3)
(49.6)
(45.5)
(99.5)
131.7
500.9
319.7
1648.4
Mesic
12.1
4.6
.1
478.6
53
355
10
515
(0.3)
(0.1)
(0.0)
(13.5)
(23.1)
(117.0)
(5.6)
(117.8)
65.1
359.6
10.1
993.6
5.4
0.0
79.7
2269.5
7
359
60
1498
(0.2)
(0.0)
(2.2)
(63.9)
(6.6)
(37.5)
(18.1)
(347.5)
12.4
359
139.7
3767.5
Year indicates age of fire referenced to 2005.
3.3. Young stand recovery
The young recovering stands on all units were likely a mix of
natural regeneration and planting, and the two sources of origin
could not be separated. There was a low density of regeneration
with measurable breast-high diameter, averaging less than
100 stems ha1, on all units except for the Entiat (35 years) fire
(Table 2). Regeneration was almost exclusively P. ponderosa and P.
menziesii. On the Entiat fire, Pinus contorta was a codominant
species, and the average density was over 1200 stems ha1. Total
tree density, including trees below breast height, suggest adequate
to overstocked conditions in post-fire years 11–35 on all but the
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
3.4. Temperature profiles around logs
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
consumption increased from 52 and 59.2% consumption in early
season to 70.8 and 74.3% in late season burns. Soil moisture was
equivalent to air-dry conditions (<5%). Mean maximum surface
temperatures spiked early in the flaming period for both small
diameter (Fig. 5) and large diameter (Fig. 6) logs, and gradually
decreased as more smoldering combustion occurred. In all
conditions, mean maximum surface temperatures were well
above lethal temperatures for cambial tissue. Mean maximum
surface temperatures for diameter class (P = .504), decay class
(P = .065), and thermocouple location (P = .057) did not differ.
Lethal temperatures were reached out to 10 cm distance from
each log edge. Logs burned in late season, however, did show
higher surface temperatures than those burned in early season
(P = .000).
Thermocouples buried at depth under small diameter (Fig. 7)
and large diameter (Fig. 8) logs showed more differences. There
were differences in mean maximum temperatures due to depth
(P = .000), diameter class (P = .001), decay class (P = .043), and
season (P = .006), with a diameter season interaction (P = .005).
Mean maximum temperature decreased with depth (Fig. 9), and
lethal temperatures were reached on all early season logs to 5 cm
depth but not deeper. Large logs, rotten logs, and late season burns
had higher temperatures than small logs, sound logs, and early
season burns. Large logs burned in late season reached lethal
3957
temperatures to 15 cm depth, but small logs, regardless of decay
class, reached lethal temperatures only down to 5 cm.
3.5. Effects of soil heating on root surrogates
Mean bark thickness of the Douglas-fir live branch dowels used
as root surrogates was 1.2 mm (S.D. 0.4 mm). All control dowels,
cut at the same time as treatment dowels and refrigerated
overnight with them, showed no cambial damage when measured
the next day. In most treatment combinations, a majority of the
dowels showed signs of cambial damage (Table 3). Directly
beneath logs, 83 of 108 surrogate roots had dead tissue (Table 4).
There were no differences in the frequency of mortality with depth
directly under the log (Table 3a; x2 = 3.85, x2 critical = 5.99). There
were also no differences between the frequency of mortality
between dowels buried at 5 cm depth and 10 cm depth between
locations directly under the log and at 10 cm distance from the
edge of the log(x2 values of 0.84 and 3.65 compared to x2 critical
value of 3.84).
3.6. Lethal zone of cover from burning logs
Given the results of the root surrogate treatment, the lethal
zone for roots, even those not right at the surface, extended a
minimum of 10 cm away from each edge of the burning log.
Therefore, an additional 20 cm was added to each log diameter
measured on the log transects on the four study units, and an
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
A. A 2 3 contingency table for surrogate roots directly beneath logs
Live
5
8
12
Dead
31
28
24
Total
36
36
36
Total
25
83
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
Fig. 9. Maximum temperatures (8C) reached from the surface to 15 cm depth
directly under burning logs.
actual cover of logs was 10.2% on the 35-year-old unit (mesic
unsalvaged at Entiat), and this increased to a lethal cover up to
24.7% when the additional lethal heating zone was added. Salvaged
sites within the Entiat unit averaged about 12% lethal cover, with
little difference between aspects.
36
36
72
10 cm from edge
Total
Location at 10 cm depth
Log center
C. A 2 2 contingency table for surrogate roots buried at 10 cm depth directly
under the log and at 10 cm distance from the edge of the log
Live
11
19
30
Dead
25
17
42
Total
36
36
72
4. Discussion
Stand-replacing fires, while historically uncommon in dry
forests of the American West, were historically the norm in wet
and/or cold forests (Romme, 1982; Agee, 1993). ‘‘Boom and bust’’
patterns, beginning with large increments of coarse woody debris
immediately after the fire, followed by decreases due to decomposition and lack of new input from the young, small post-fire
trees, and eventual increases when the new forest produced trees
large enough to persist as logs, created a U-shaped distribution of
coarse woody debris over centuries (Harmon et al., 1986; Agee and
Huff, 1987). Much lower and less variable coarse woody debris
patterns were characteristic of historic P. ponderosa forests (Agee,
2002). With the change in fire regime from low-severity to mixedor high-severity, seasonally dry forests being burned now by
intense fires have biomass and cover of coarse woody debris at
many times historical levels (Agee, 2002; Skinner, 2002). For
example, cover of logs in old-growth P. ponderosa stands of central
Oregon and northern California was 1.7% (Youngblood et al., 2004),
and a study in old growth Pinus jeffreyi forest in Mexico calculated a
log cover of 1.5% (Stephens et al., 2007). Ohmann and Waddell
(2002) estimated percent cover of logs between 12 and 50 cm
diameter in young, mature, and old-growth forests to be 1.1, 1.3,
and 1.0% for P. ponderosa forests of Oregon and Washington. Our
mean percent cover of logs, by post-wildfire age 35, ranged from
4.8 to 10.2% 35 years after wildfire (Table 1), much higher than in
old growth stands of dry forests and at levels higher than suggested
to optimize protection of soils and wildlife habitat while mitigating
fire danger (Brown et al., 2003).
These fire-prone environments are dry enough that natural
decomposition is slow. Using Olson’s (1963) single exponential
decay model and the decay rate constant of 0.073 for P. ponderosa
(>25 cm) (Harmon et al., 1986), snag bole fragmentation could
take more than 40 years, and this rate appears to close to what we
observed at the 35-year-old Entiat fire (Fig. 3). However, this
process was nearly the same on the 11-year-old Tyee fire, so that
local factors likely create substantial variability on the conversion
of snags to down logs. Parminter (2002) estimated a decay rate for
log boles of 0.035, and McIver and Ottmar (2007) used 0.03 and
0.02 for P. ponderosa and P. menziesii logs. These rates would result
in 100–150 years for a population of logs to decompose. During
that time, the stands remain at risk to wildfire. Early in succession
(ages 0–30) the young trees are small enough that regardless of
coarse woody debris loads, high-severity fire is likely to occur if
another wildfire burns through the stand (McIver and Ottmar,
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
Early sound
Late rotten
Late sound
100
33
100
80
75
33
100
80
75
100
100
80
50
33
100
80
50
0
100
80
Small diameter logs
Early rotten
Early sound
Late rotten
Late sound
100
75
100
100
80
75
80
80
80
75
100
80
60
50
80
80
0
25
60
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
are consistent with what Donato et al. (2006) and McIver and
Ottmar (2007) found with fine woody debris: salvage logging
immediately increases the biomass of woody debris on the ground.
At the Fischer fire, this biomass consisted of lopped and scattered
tops left after the salvage logging. The convergence of levels of fine
woody debris between salvaged and unsalvaged stands suggested
by McIver and Ottmar (2007) occurred in our study with coarse
woody debris. By age 10, levels of coarse woody debris in salvaged
stands fell below those of unsalvaged stands, and that pattern
remained through age 35. Salvage removes boles that would
otherwise become coarse woody debris, so one would expect
lowered coarse woody debris levels decades after salvage logging
compared to unsalvaged sites.
The difference in percent cover of coarse woody debris between
salvaged and unsalvaged stands at the 35-year-old Entiat fire
ranged from 1.6 (dry aspects) to 5.3% (mesic aspects). When the
lethal cover was calculated, these differences increased to 1.9 (dry
aspects) to 13.3% (mesic aspects), and almost 25% lethal cover
occurred on unsalvaged mesic aspects at the Entiat fire. These
values suggest that prescribed fire introduced for the purpose of
lowering wildfire risk could significantly damage young stands,
even if crown damage was minimal, due to root damage, as has
been demonstrated for old growth pine stands (Swezy and Agee,
1991; Kolb et al., 2007). On dry aspects, which might be chosen as a
higher priority for young stand fuel treatments, salvage appeared
to have a less dramatic effect than on the mesic aspects.
We used live Douglas-fir branches as surrogates for small roots
(1.25 cm and smaller). We justified this on the basis that in situ
experiments were not easily designed, and that small branches
should function similarly to roots in a physiological sense. Our
controls indicated that a cut branch left out for the day and
refrigerated overnight showed no cambial damage the next day.
We were confident that the root surrogate treatment would be a
better test of root damage than temperature profiles alone, and the
results suggested substantial damage could occur to roots not only
beneath burning logs but also adjacent to them. Our tests were
conservative, as we used a single log model. When large woody
fuels burn in isolation, as in our experiments, they may burn with
less intensity or less completely than when burned in close
proximity to other sufficiently dry fuels of the same size or smaller
(Albini and Reinhardt, 1995, 1997). Harrington (1981) observed
that grouped logs burned more completely than when they burned
in isolation. Therefore, the temperature profiles we measured are
likely conservative, as we only burned single logs. We did not
extend our measurement zone beyond 10 cm from the edge of logs,
so we did not extrapolate potential damage further away from the
burned logs.
4.1. Management considerations
Some managers have considered breaking the cycle of stand
replacement burning (e.g., Thompson et al., 2007) by intervening
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
suppression should a wildfire occur, create adequate space for
tree growth, and reduce potential wildfire severity in the young
stand. Conducting prescribed fires in young stands with substantial coarse woody debris presents several challenges, including
the amount of smoke from smoldering logs (Hardy et al., 2001). But
one underappreciated effect is the potential root damage from
consumption of coarse woody debris from prescribed fires
intended to reduce fuels and make the young stand more resistant
to wildfire. Busse et al. (2005) showed that burning masticated
residues up to 12.5 cm deep created lethal surface temperatures
that increased with soil dryness and mulch depth. Lethal
temperatures were observed down to 10 cm depth in the heavier
mulch treatment, and they suggested burning these residues
ranked between moderate severity prescribed fires and damaging
effects of heavy slash fires. The spatial distribution of wood mulch
at one site showed that about 25% of the area would experience
lethal temperatures to 10 cm depth, but at another site the mulch
depths were less and lower soil heating would be predicted there.
Whether stands have been salvaged or not, soil heating from
smoldering logs will be a concern. Salvage reduces but does not
eliminate coarse woody debris. Some coarse woody debris will be
valuable for wildlife habitat (Brown et al., 2003), and some will be
too small to be commercially useful. Spring burning may be one
solution where high levels of coarse woody debris occur. Our data
suggest that spring burns had less heating than fall burns, and early
season burns typically cover less area. If we had used moist soil
under the logs burned in late spring, the differences likely would
have been even more pronounced (Frandsen and Ryan, 1986).
Perrakis and Agee (2006) reported for old-growth forest a range of
19–37% area burned from spring burns with a much higher 64–86%
for fall burns. Spring burns typically consume less coarse woody
debris, too. Knapp et al. (2005) reported 57% of log biomass
consumed in spring burns compared to 83% in fall burns, again in
old-growth forest. Spring prescribed burns in the 1970 Entiat fire,
under young stands, showed similar patchiness (Peterson et al.,
2007). All of the forest floor was consumed over 45% of the area,
between 5 and 95% was consumed on 27% of the area, and 28% of
the area was unburned. It would seem prudent that for mesic
aspects in unsalvaged areas, initial prescribed burns in spring
would be favored to mitigate the effect of root heating from
smoldering logs. Subsequent fires in such areas, and initial fires in
salvaged stands, might have wider seasonal windows for burning.
In the past, most concerns regarding salvage logging have dealt
with short-term issues (Beschta et al., 2004). Longer-term
ecological effects, such as some of the effects of excessively high
levels of coarse woody debris, should be factored into the decisionmaking process. In dry forest types there may be some long-term
advantages for managers if excessive coarse woody debris loads
are reduced early in the post-wildfire period.
Acknowledgements
This research was funded under Joint Venture Agreement PNW
#03-JV-11261927-534, CROP Forest Ecology, between the USDA
Forest Service, Pacific Northwest Research Station and the
University of Washington. Logistical support was provided by
the Okanogan-Wenatchee National Forest and Wenatchee Forestry
Sciences Laboratory. D.W. Peterson graciously loaned us the
temperature dataloggers. Field work was provided by R. Wiedemer, C. Raynham, and D. Anderson. Reviews of an earlier draft were
graciously provided by M. Busse, D.W. Peterson, M. Dahlgreen, and
J. McIver.
References
Agee, J.K., 1993. Fire Ecology of Pacific Northwest Forests. Island Press, Washington,
DC.
Agee, J.K., 1998. The landscape ecology of western forest fire regimes. Northw. Sci.
72, 24–34.
Agee, J.K., 2002. Fire as a coarse filter for snags and logs. In: Laudenslayer Jr., W.F.,
Shea, P.J., Valentine, B.E., Weatherspoon, C.P., Lisle, T.E. (tech. coords.), Proceedings of the Symposium on the Ecology and Management of Dead Wood in
Western Forests. USDA Forest Service General Technical Report PSW-GTR-181,
pp. 359–368.
Agee, J.K., Huff, M.H., 1987. Fuel succession in a western hemlock/Douglas-fir forest.
Can. J. For. Res. 17, 697–704.
P.G. Monsanto, J.K. Agee / Forest Ecology and Management 255 (2008) 3952–3961
Agee, J.K., Maruoka, K., 1994. Historical Fire Regimes of the Blue Mountains. Tech.
Note BMNRI-TN-1. Blue Mountains Natural Resources Institute, La Grande, OR,
4 pp.
Albini, F.A., Reinhardt, E.D., 1995. Modeling ignition and burning rate of large woody
natural fuels. Int. J. Wildland Fire 5 (2), 81–91.
Albini, F.A., Reinhardt, E.D., 1997. Improved calibration of a large fuel burnout
model. Int. J. Wildland Fire 7 (1), 21–28.
Bate, Lisa, J., Torgersen, Torolf, R., Wisdom, Michael, J., Garton, Edward, O., 2004.
Performance of sampling methods to estimate log characteristics for wildlife.
For. Ecol. Manage. 199, 83–102.
Bell, J.F., Dilworth, J.R., 2002. Log Scaling and Timber Cruising. Cascade Printing
Company, Corvallis, OR.
Beschta, R.L., Rhoades, J.J., Kauffman, J.B., Gresswell, R.E., Minshall, G.W., Karr, J.R.,
Perry, D.A., Hauer, F.R., Frissell, C.A., 2004. Postfire management on forested
public lands of the western United States. Conserv. Biol. 18, 957–967.
Brown, J.K., 1974 Handbook for Inventorying Downed Woody Material. USDA Forest
Service General Technical Report INT-GTR-16.
Brown, J.K., Reinhardt, E.D., Kramer, K.A., 2003. Coarse Woody Debris: Managing
Benefits and Fire Hazard in the Recovering Forest. USDA Forest Service General
Technical Report RMRS-GTR-105.
Busse, M.D., Hubbert, K.R., Fiddler, G.O., Shestak, C.J., Powers, R.F., 2005. Lethal soil
temperatures during burning of masticated forest residues. Int. J. Wildland Fire
14, 267–276.
Covington, W.W., Moore, M.M., 1994. Southwestern ponderosa forest structure:
changes since Euro-American settlement. J. For. 92 (1), 39–47.
Covington, W.W., Everett, R.L., Steele, R., Irwin, L.L., Daer, T.A., Auclair, A.N.D., 1994.
Historical and anticipated changes in forest ecosystems of the inland west of the
United States. J. Sustain. For. 2 (1), 13–63.
Donato, D.C., Fontaine, J.B., Campbell, J.L., Robinson, W.D., Kauffman, J.B., Law, B.E.,
2006. Post-wildfire logging hinders regeneration and increases fire risk. Science
311, 352.
Dutton, C.E., 1881. Physical Geology of the Grand Canyon District. U.S.D.I. Geological
Survey Second Annual Report. Government Printing Office, Washington, D.C.,
pp. 49–166.
Everett, R.L., Schellhaas, R., Keenum, D., Spurbeck, D., Ohlson, P., 2000. Fire history in
the ponderosa pine/Douglas-fir forests on the east slope of the Washington
Cascades. For. Ecol. Manage. 129, 207–225.
Frandsen, W.H., Ryan, K.C., 1986. Soil moisture reduces belowground heat flux and
soil temperatures under a burning fuel pile. Can. J. For. Res. 16, 244–248.
Hardy, C.C., Ottmar, R.D., Peterson, J., Core, J.E., Seamon, P. (Eds.), 2001. Smoke
Management Guide for Prescribed and Wildland Fire: 2001 edition PMS 420-2.
NFES 1279. National Wildfire Coordination Group, Boise, ID, 226 pp.
Hare, R.C., 1961. Heat Effects on Living Plants USDA Forest Service, Southern Forest
Experiment Station, Occasional Paper 183.
Harmon, M.E., Franklin, J.F., Swanson, F.J., Sollins, P., Gregory, S.V., Lattin, J.D.,
Anderson, N.H., Cline, S.P., Aumen, N.G., Sedell, J.R., Lienkaemper, G.W., Cromack
Jr., K., Cummins, K.W., 1986. The ecology of coarse woody debris. Adv. Ecol. Res.
15, 133–302.
Harrington, M.G., 1981. Preliminary Burning Prescriptions for Ponderosa Pine Fuel
Reductions in Southeastern Arizona. USDA Forest Service Research. Note RM402.
Heyerdahl, E.K., Brubaker, L.B., Agee, J.K., 2001. Annual and decadal climate forcing
on historical fire regimes in the interior Pacific Northwest, USA. Holocene 12,
597–604.
Knapp, E.E., Keeley, J.E., Ballenger, E.A., Brennan, T.J., 2005. Fuel reduction and coarse
woody debris dynamics with early season and late season prescribed fire in a
Sierra Nevada mixed conifer forest. For. Ecol. Manage. 208, 383–397.
Kolb, T.E., Agee, J.K., Fule, P.Z., McDowell, N.G., Pearson, K., Sala, A., Waring, R.H.,
2007. Perpetuating old ponderosa pine. For. Ecol. Manage. 249, 141–157.
Lillybridge, T.R., Kovalchik, B.L., Williams, C.K., Smith, B.G., 1995. Field Guide for
Forested Plant Associations of the Wenatchee National Forest. USDA Forest
Service General Technical Report PNW-GTR-359. Portland, OR.
Lindenmayer, D.B., Foster, D.R., Franklin, J.F., Hunter, M.L., Noss, R.F., Schmiegelow,
F.A., Perry, D., 2004. Salvage harvesting policies after natural disturbance.
Science 305, 1303.
Lolley, M., 2005. Wildland Fuel Conditions and Effects of Modeled Fuel Treatments
on Wildland Fire Behavior and Severity in Dry Forests of the Wenatchee
Mountains. M.S. Thesis. University of Washington, Seattle, WA.
3961
Maser, C., Anderson, R., Cromack Jr., K., Williams, J.T., Martin, R.E., 1979. Dead and
downed woody material. In: Thomas, J.W. (Ed.), Wildlife Habitats in Managed
Forests. The Blue Mountains of Oregon and Washington, USDA Forest Service
Agricultural Handbook 553. Washington, D.C., pp. 79–85.
McIver, J.D., Ottmar, R., 2007. Fuel mass and stand structure after post-fire logging
of a severely burned ponderosa pine forest in northeastern Oregon. For. Ecol.
Manage. 238, 268–279.
McIver, J.D., Starr, L. (tech. Eds.), 2000. Environmental Effects of Post Fire Logging:
Literature Review and Annotated Bibliography. USDA Forest Service General
Technical Report PNW-GTR-486.
McNeil, R.C., Zobel, D.B., 1980. Vegetation and fire history of a ponderosa pine-white
fir forest in Crater Lake National Park. Northw. Sci. 54, 30–46.
Natural Resources Conservation Service, 2007. United States Department of Agriculture. Official Soil Series Descriptions [Online WWW]. Available URL: ‘‘http://
soils.usda.gov/technical/classification/osd/index.html’’ (Accessed 05/12/2007).
Ohmann, J.L., Waddell, K.L., 2002. Regional Patterns of Dead Wood in Forested
Habitats of Oregon and Washington. USDA Forest Service General Technical
Report PSW-GTR-181.
Olson, J.S., 1963. Energy storage and the balance of producers and decomposition in
ecological systems. Ecology 44, 332–341.
Parminter, J., 2002. Coarse woody debris decomposition – principles, rates, and
models. In: Presented to: Northern Interior Vegetation Management Association (NIVMA) and Northern Silviculture Committee (NSC) Winter Workshop:
Optimizing Wildlife Trees and Coarse Woody Debris Retention at the Stand and
Landscape Level. January 22–24, 2002. Prince George, B.C.
Passovoy, M.D., Fule, P.Z., 2006. Snag and woody debris dynamics following severe
wildfires in northern Arizona ponderosa pine forests. For. Ecol. Manage. 223,
237–246.
Perrakis, D.D.B., Agee, J.K., 2006. Seasonal fire effects on mixed-conifer forest
structure and ponderosa pine resin properties. Can. J. For. Res. 36, 238–254.
Peterson, D.W., Hessburg, P.F., Salter, B., James, K.M., Dahlgreen, M.C., Barnes, J.A.,
2007. Reintroducing fire in regenerated dry forests following a stand-replacing
wildfire. In: Powers, R.F. (tech. Ed.), Restoring Fire-Adapted Ecosystems: Proceedings of the 2005 National Silviculture Workshop. USDA Forest Service
General Technical Report PSW-GTR-203, pp. 79–86.
Ryan, K.C., Peterson, D.L., Reinhardt, E.D., 1988. Modeling long-term fire-caused
mortality in Douglas-fir. For. Sci. 34, 190–199.
Romme, W.H., 1982. Fire and landscape diversity in subalpine forests of Yellowstone National Park. Ecol. Monogr. 52, 199–221.
Skinner, C., 2002. Influence of fire on the dynamics of dead woody material in forests
of California and southwestern Oregon. In: Laudenslayer Jr., W.F., Shea, P.J.,
Valentine, B.E., Weatherspoon, C.P., Lisle, T.E. (tech. coords.), Proceedings of
the Symposium on the Ecology and Management of Dead Wood in Western
Forests. USDA Forest Service General Technical Report PSW-GTR-181, pp. 445–
454.
Stephens, S.L., Fry, D.L., Franco-Vizcaı́no, E., Collins, B.M., Moghaddas, J.M., 2007.
Coarse woody debris and canopy cover in an old-growth Jeffrey pine-mixed
conifer forest from the Sierra San Pedro Martir, Mexico. For. Ecol. Manage. 240,
87–95.
Swezy, D.M., Agee, J.K., 1991. Prescribed fire effects on fine root and tree mortality in
old-growth ponderosa pine. Can. J. For. Res. 21, 626–634.
Thompson, J.R., Spies, T.A., Ganio, L.M., 2007. Reburn severity in managed and
unmanaged vegetation in a large wildfire. Proc. Natl. Acad. Sci. U.S.A. 104 (25),
10743–10748.
Weaver, H., 1943. Fire as an ecological and silvicultural factor in the ponderosa pine
region of the Pacific slope. J. For. 41 (1), 7–15.
Westerling, A., Hidalgo, H.G., Cayan, D.R., Swetnam, T.W., 2006. Warming and
earlier spring increases western U.S. forest wildfire activity. Science 313,
941–943.
Western Regional Climate Center, 2003. Washington Climate Summaries. Desert
Research Institute, Reno, NV. http://www.wrcc.dri.edu/summary/climsmwa.html (accessed 04/28/2006).
Wright, C.S., Agee, J.K., 2004. Fire and vegetation history in the eastern Cascade
mountains, Washington. Ecol. Appl. 14, 443–459.
Youngblood, A., Max, T., Coe, K., 2004. Stand structure in eastside old-growth
ponderosa pine forests of Oregon and northern California. For. Ecol. Manage.
199, 191–217.
Zar, J.H., 1999. Biostatistical Analysis, 4th ed. Prentice Hall, Upper Saddle River, NJ.