Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 68
PATTERNS IN LIGHTNING-CAUSED FIRES AT GREAT SMOKY MOUNTAINS NATIONAL PARK
Dana Cohen1, *, Bob Dellinger2, Rob Klein2, Beth Buchanan3
1North Kaibab Ranger District, Kaibab National Forest, USDA Forest Service, Fredonia, AZ 86022
2Great Smoky Mountains National Park, National Park Service, Gatlinburg, TN 37738
3Southern Region, USDA Forest Service, Asheville, NC 28801
*Corresponding author: Tel.: (928) 643-8141; e-mail: [email protected]
ABSTRACT
Fires that burn unimpeded behave differently than suppressed or prescribed (management-ignited) fi res. Studying this fi re behavior increases our understanding of historic fi re regimes. Wildland fi re use policy allows for managing lightning-caused fi res for resource benefi t without suppressing them provided specifi c pre-defi ned conditions are met. Great Smoky Mountains National Park has managed ten fi res under this policy from 1998 to 2006. Data from these fi res and data from park fi re reports for suppressed lightning-caused fi res since 1940 were examined to illustrate patterns for non-anthropogenic fi res. Lightning-caused fi res occurred most frequently during the growing season and many persisted through numerous precipitation events. Unsuppressed fi res had long durations (up to 38 days) and exhibited a wider range of fi re behavior than found by previous studies for lightning-caused fi res in the region. These unsuppressed fi res exhibited the largest perimeter growth in periodic bursts of higher-intensity behavior; yet smoldered and crept through the majority of the active burning window. The total area burned by the ten fi res managed under the wildland fi re use policy from 1998 to 2006 (787 ha) has surpassed the aggregate within-park acreage of 122 suppressed lightning-caused fi res over the previous 56 years (523 ha).
Keywords: fi re, fi re duration, fi re regimes, fi re suppression, Great Smoky Mountains National Park, lightning, southern Appalachians, wildland fi re use
Citation: Cohen, D., B. Dellinger, R. Klein, and B. Buchanan. 2007. Patterns in lightning-caused fi res at Great Smoky Mountains National Park. Fire Ecology 3(2): 68-82.
INTRODUCTION West until the 1920s and underestimated for grasslands through the mid-1980s (Komarek The identifi cation of lightning as an 1968, Baker 2002). Eastern deciduous forests important ignition source gained acceptance in general and the southern Appalachians in slowly over the last century in the United particular have not escaped this evolution States. For instance, the idea was not widely of understanding. Great Smoky Mountains accepted for forests in the Rocky Mountain National Park (GSMNP) studies in the Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 69
1980s classifi ed all burned areas, regardless spp.), and pines (Pinus spp.) have experienced of ignition source, as non-“virgin” forests; a substantial drop in recruitment since the mid- implicitly denying the role of fi re as a regular 1900s. The decline of fi re-dependent Table forest process in park ecosystems (Pyle 1985, Mountain pine (Pinus pungens) has been 1986). The 1902 U.S. Forest Service report on well documented (Zobel 1969, Van Lear and the southern Appalachians acknowledges only Waldrop 1989, Williams 1998, Barden 2000, anthropogenic sources of fi re with no mention Welch and Waldrop 2001). Conversely, fi re- of lightning-caused ignitions (Roosevelt 1902). sensitive, shade-tolerant species such as red In a 1942 letter to the Chief of Forestry for maple (Acer rubrum), eastern hemlock (Tsuga the National Park Service, the fi rst GSMNP canadensis), and black gum (Nyssa sylvatica) Superintendent, J. R. Eakin, wrote, “I am have increased across the landscape (Abrams learning new things about fi re here. Until a few et al. 1995, Russell 1997, Brose and Van Lear years ago I thought lightning would not start 1999, Harrod and White 1999, Abrams 2006). fi res” (Eakin 1942). Baker (2002) attributes National Park Service monitoring data from the change in perception to several factors, plots in GSMNP support these trends (NPS particularly the growth of forest management 2001) (Figure 1). Fire regime changes are also practices, proliferation of trained observers, corroborated by the former presence of red- and systematic data collection. cockaded woodpecker (Picoides borealis), in Although it is now commonly understood GSMNP until the early 1980s when decades of that lightning causes fi res in eastern deciduous fi re suppression led to the collapse of open pine systems (Komarek 1966, Barden and Woods habitat and woodpecker populations (Dimmick 1973, Ruffner and Abrams 1998, Petersen and et al. 1980). Drewa 2006), there is very little published The purpose of this study was to augment information regarding lightning-caused fi res, the current knowledge base for lightning- their behavior, and their effects in these caused fi res in the southern Appalachian region forests. Furthermore, there have been few with recent experience from GSMNP. The opportunities in these forests to observe park’s WFU program has provided a valuable lightning-caused fi res from ignition through and unparalleled opportunity to observe fi res natural extinction. The full implementation of persisting without traditional suppression wildland fi re use (WFU) policy at GSMNP— actions and to document their characteristics whereby lightning-caused fi res are managed for their ecological benefi ts instead of being 10000 suppressed—has provided an opportunity to Other trees document characteristics of lightning-caused 1000 Oak fi res in this region and defi ne patterns key -1 Pine to understanding the ecological role of non- 100
anthropogenic fi res, both historically and for Stems ha the future (Arno and Fiedler 2005). 10 Fire’s natural role as an important ecological 1 process in the southern Appalachians is perhaps <10 10-20 20-30 30-40 40-50 >50 best illustrated by the decline of numerous species since the advent of fi re suppression Diameter class (cm) (Van Lear and Waldrop 1989, Abrams 1992, Figure 1. Frequency distribution by size class Lorimer 1993, Frost 2000). Regionally of oak, pine and other trees (e.g., red maple, black gum). Data compiled from GSMNP fi re dominant oaks (Quercus spp.), hickories (Carya effects monitoring 0.1 ha plots, n = 57. Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 70
in a modern landscape. The park currently parks in the country. Vegetation ranges from has the largest dataset for unsuppressed fi res xeric, Table Mountain pine (Pinus pungens) in the region, as the U.S. Forest Service ridgetops through oak- (Quercus) dominated implemented WFU fi res in eastern National side slopes, to biologically rich, mixed Forest System lands for the fi rst time in 2006. mesophytic toe slopes and coves (Whittaker Because the dataset from the ten fi res managed 1956). The park is designated as part of an thus far is too small for meaningful statistical International Biosphere Reserve and a World analysis, this paper focuses on the qualitative Heritage site because it serves as an outstanding information collected from case studies that example of the eastern deciduous biome. demonstrate patterns in lightning-caused fi res A wide variety of natural process (blow in the southern Appalachians. Fire monitoring downs, ice storms, fi re, insects, and disease) and report data were analyzed to identify and human activities (agriculture, logging, patterns that enhance our understanding of fi re and development) have marked the GSMNP regimes in these forests. landscape over time. The area has been long inhabited by humans, fi rst Native Americans STUDY AREA and later European immigrants. It remained virtually untouched by lumber interests until Great Smoky Mountains National Park 1880, with full-scale logging operations encompasses over 200,000 ha (519,000 ac) of beginning in the early 1900s. Over 3.54 forested lands in the southern Appalachians million m3 (1.5 billion board feet) of lumber along the border of North Carolina and were removed from the area that became Great Tennessee. Though the park was offi cially Smoky Mountains National Park (Lambert established in 1934, it was fi rst administered 1961). However, the rugged topography by the federal government in 1931 (Frome made much of the park inaccessible to loggers 1994). This administration included organized and up to 40 % of the lands within the park law enforcement, development for tourism, boundaries are considered virgin (Stupka 1960, natural history interpretation, and suppression Pyle 1985). A strong relationship has existed of all fi res. between humans and fi re (Pyne 1982) and fi re The Great Smoky Mountains are part of the ignitions within the park were elevated through Unaka range, a western extension of the Blue human activities (Van Lear and Waldrop 1989, Ridge Province (Fenneman 1938). The park Hays 1993, Delcourt and Delcourt 1997). ranges in elevation from 270 m (888 ft) to 2,025 The WFU policy for GSMNP has m (6,643 ft). Annual precipitation averages developed over several decades. The national 147 cm (58 in) at lower elevations and 231 cm push to return natural processes, particularly (91 in) at the highest elevations, with monthly fi re, throughout the National Park Service precipitation peaking in January and August. was diffi cult and required public education, Mean minimum temperatures reach from -5 Congressional persuasion, and managerial °C to 0 °C (23 °F to 32 °F) from November acceptance (Hendrickson 1973). The effort through March. Mean temperatures peak in began in earnest in the early 1960s with the July and range from 20 °C to 30 °C (68 °F to Leopold Report (Leopold et al. 1963, Sellars 86 °F). Temperatures decrease with elevation, 1997) and is refl ected in the GSMNP 1969 yet the lapse rate diminishes in winter months Resources Management Plan. In this plan, and at higher elevations (Shanks 1954). These the park addressed “over protection of [the] factors combine to provide a backdrop for one ecosystem from natural fi res” as a problem of the most productive and naturally diverse and recommended that lightning-ignited fi res Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 71
“run their natural course” when they posed data for 1931 to 1939, therefore those years no threat to lives or property (NPS 1969). were not included in this analysis. Specifi c This aspect of the 1969 plan was never reports were missing for 1940, 1941, and 1955 implemented offi cially. The experimental to 1959. The park fi re atlas, detailed tabular 1976 Polecat Ridge fi re, which was monitored summary reports, annual forestry reports to the until naturally extinguished, was described as regional offi ce, and Harmon’s (1981) study for an “unoffi cial switch from a strict suppression these years were used to complete and verify policy” (Harmon 1981). In 1979, a detailed the fi nal dataset. Reported area burned in this report from Resource Management Specialist study was limited to lands inside the park’s Stuart Coleman to the Park Superintendent boundary. Fires that burned wholly outside the again advocated for managing lightning fi res park were excluded from the analysis. within pre-defi ned boundaries to restore Although the fi rst WFU fi re didn’t offi cially natural processes (Coleman 1979). However, occur until 1998, two lightning-ignited fi res despite these management discussions and the in the 1970s were not suppressed in an early clearly identifi ed need, the policy of managing attempt to change park fi re management policy lightning-caused fi res for resource benefi t was to what is now WFU. The 1976 Polecat Ridge not formally realized until after the adoption of Fire was one of these fi res (Harmon 1981). The the park’s fi rst fi re management plan in 1996. other fi re was not explicitly identifi ed in reports but notes included in the fi re report suggest it METHODS was the 1977 Polecat Ridge Fire. These two fi res were not included in the suppression- Fire History Data era lightning fi re statistics for total number of suppressed fi res, size, or duration. When the Data for lightning-ignited fi res from 1940 area of the 1976 Polecat Ridge Fire is included to 2006 were used to examine trends in area in unsuppressed-lightning fi re data, it is noted. burned in GSMNP. These data were compiled The 1977 Polecat Ridge Fire was not included from the Shared Application Computer System in the unsuppressed fi re discussions due to (SACS) database of the Department of the incomplete data. Interior, now the Wildland Fire Management Reporting of fi re size has varied during Information (WFMI) database, which is the the period of this study. In the early days of offi cial fi re-reporting system for the National park management, fi re size was reported to Park Service. This database contains basic fi re the hundredth of an acre and single-tree fi res information including name, start date, date were reported as “Neg.” or negligible. More declared out, cause, and size. Latitude and recently, fi res have been documented with 0.04 longitude are included for records dating from ha (0.1 ac) as a minimum reporting size. For 1974 to the present. These data were error- this paper, early data have been modifi ed to checked using published literature (Harmon meet more recent standards, rounding from 1981), original fi re reports, park fi re atlases, hundredths to tenths and using 0.04 ha (0.1 ac) and other internal administrative documents. as the minimum fi re size. Any corrections made to the original dataset WFU fi re monitoring has included collection were confi rmed with a minimum of two of fi re behavior information, perimeter growth, sources. Original fi re reports were available and onsite weather data. Through 2006, the for most of the study period and were the fi res managed under the park’s WFU policy preferred tool for verifi cation. Not enough have received no management action that might information was available to verify the extant artifi cially distort fi re growth or behavior. Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 72
There were no burn-out operations or control (Table 2). Of the suppressed lightning fi res, lines (Cohen and Dellinger 2006). only the 1988 Redman Fire grew to over 40.5 ha (100 ac), however, according to the fi re Fire Report Narratives report, an unknown portion of the total area burned on this fi re was due to fi re-containment Hardcopy fi re reports from 1942 to operations in conjunction with indirect line the present contain narratives recorded by construction. The majority of suppressed fi refi ghters or the local park ranger (often the lightning fi res averaged between 0.1 ha (0.25 same individual) at the time of the fi re, or ac) and 40.5 ha (100 ac), with a median value shortly thereafter. Many of these narratives of 2 ha (5 ac) and a mean of 5.7 ha (14.2 ac). are rich with information about fi re behavior, The 10 recent unsuppressed fi res are currently local vegetation, and fuel conditions. They evenly distributed in terms of size, with four often contain detailed descriptions of weather fi res <0.1 ha (0.25 ac), and four at >40.5 ha conditions, fi re progression, scouting reports, (100 ac) (Table 3). and management actions. All fi re reports for Since 1940, there were 18 years with no lightning-caused fi res were read and those lightning-caused fi res and nine years with fi ve with detailed narratives were identifi ed. This or more that burned inside the park (Figure subset was evaluated for use as case studies. 2) (Barden and Woods 1973, Coleman 1979, To insure that the sample fi res spanned the Harmon 1981). The highest number of range of management policies, at least one fi re lightning-caused fi res (11) occurred in 1988. per decade from the1940s to the1980s with a Lightning-caused fi res have occurred in each duration greater than 4.5 days was selected. month of the year except February and October Fire reporting and management changes (e.g., (Figure 3). Ninety percent of all lightning- narratives with little or no description of the caused fi res at GSMNP occurred during the vegetation; indirect fi re line construction) growing season from April through August, in the 1980s made it diffi cult to discern fi re consistent with storm-event frequency within behavior characteristics useful for case studies the region (cf. Peterson and Drewa 2006). The from this decade. distribution for timing of lightning-caused fi re starts has shifted slightly toward spring RESULTS in recent years. Of 16 total starts since 1998, April had the highest total with six recorded. Lightning-caused Fire Data Four of the 10 unsuppressed fi res occurred in April (Table 3). The large unsuppressed 1976 Though the fi re management policy Polecat Ridge Fire, not included in the above allowing WFU was adopted by GSMNP in count, occurred in July. 1996, the fi rst WFU fi re did not occur until 1998. From 1998 to 2006, 10 of 16 lightning- Fire Behavior—Case Studies caused fi res were managed as WFU fi res. These 10 fi res burned a total of 787 ha (1,946 Distinct patterns in fi re behavior were ac), which is 264 ha (652 ac) more than the apparent between suppressed and unsuppressed total within-park area burned for the 122 lightning-caused fi res. Fire report narratives suppressed lightning fi res over the previous 56 provided examples of fi res persisting through yr period (Table 1). Mean duration and area precipitation events and becoming active after burned for unsuppressed lightning fi res were periods of dormancy. The following excerpts greater than for suppressed lightning fi res and synopses were selected from GSMNP fi re Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 73
Table 1. Suppressed lightning fi res, Great report narratives to describe the fi re behavior Smoky Mountains National Park, 1940-1997 for lightning-caused fi res in the park (NPS The 1976 and 1977 Polecat Ridge Fires have 1940-2006). They have been organized into been excluded. three groups: persistence through precipitation Number Total area Mean Mean Year of fi res burned size duration events, emergence from dormancy, and large ha ha days unsuppressed fi res. 1940-49 27 25.4 0.9 3.1 1950-59 34 98.9 2.9 2.3 Persistence through Precipitation Events 1960-69 16 56.0 3.5 4.9 Three fi res were selected to illustrate 1970-79 3 33.2 11.1 6.0 the persistence of fi res through periods of 1980-89 27 220.1 8.2 10.0 substantial precipitation. One of these fi res 1990-97 15 58.2 3.9 10.1 was a recent WFU event. Total 122 523.4 4.3 6.6 Devil’s Courthouse Ridge Fire —December 1942, 0.04 ha (0.1 ac). “A large Hemlock Table 2. Lightning-caused suppressed and wildland fi re use fi res, Great Smoky Mountains snag was struck by lightning and was set on National Park, 1998-2006. Duration for fi re during a storm of December 1. A heavy suppressed lightning-caused fi res from 1998- snow storm occurred on December 3 which 2006 is not included because the last date of fi re prevented the fi re from spreading away from activity (smoke or heat) is not well documented the snag. On December 9, Assistant Park in reports for these fi res. Warden Lollis discovered the burning snag on Number Total area Mean Mean a patrol of his district…” of fi res burned size duration ha ha days Turkeypen Ridge Fire—April 1971, 32.4 Suppressed 6 15.1 2.5 * ha (80 ac). “During the night of April 19th, a Fire use 10 787.4 1.8 17.4 violent thunderstorm passed over Cades Cove. On Turkeypen Ridge, a bolt of lightning struck a large hickory tree and set it to smoldering. Table 3. Wildland Fire Use fi res, GSMNP April 27th, in the afternoon, the top of the 1998-2006. hickory fell, scattering fi re into the dry leaves Fire Start date Duration Size around it.” days ha Forney Creek 4/6/1998 22 149.7 Shot Beech Fire—June 13-July 17, 2004; Enloe Ridge 9/8/1998 3 0.0 0.04 ha (0.1 ac). Managed as a WFU event, Collins 2 4/20/1999 9 52.6 this fi re persisted in a single standing dead Blacksmith 8/19/1999 35 211.7 hemlock for 35 days and was not extinguished Fort Harry 3/10/2000 8 0.1 until receiving a total of approximately 16 cm Cave Ridge 11/8/2000 6 0.0 (6.5 in) of rain. Ekaneetlee 4/27/2001 13 2.4 Emergence from Dormancy Wolfpen 11/11/2001 5 1.2 Shot Beech 6/13/2004 35 0.0 Three fi res were chosen to illustrate how Chilly Spring 4/3/2006 38 369.5 fi res can become active even after they are Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 74
12
10 /
8
6
4 Number of Ignitions 2
0 0 5 0 5 0 5 0 5 0 5 0 5 0 5 4 4 5 5 6 6 7 7 8 8 9 9 0 0 9 9 9 9 9 9 9 9 9 9 9 9 0 0 1 1 1 1 1 1 1 1 1 1 1 1 2 2 Figure 2. Frequency of lightning-caused fi res by year at GSMNP, 1940-2006.
40 [escaping control line] on mop up crew on that / day.” 30 Proctor Ridge Fire—May 1951, 32.8 ha 20 (81 ac). Smoke was fi rst reported by a lookout 10 tower on May 18, about 3 hours after witnessing
Number of ignitions a lightning strike in the area. Firefi ghters 0 searched for the fi re for several hours and were n b r y p ct c a e a pr a un Jul ug e ov e unable to fi nd anything. Other lookouts in the J F M A M J A S O N D area were unable to observe the smoke, and Figure 3. Frequency of lightning-caused fi res by month at GSMNP, 1940-2006. it was thought that due to an afternoon rain shower, perhaps it had been a column of fog thought to be extinguished. These fi res were instead of smoke. At approximately 1 PM on thought to be out or were or misreported after the following afternoon, another lookout saw a the initial smoke report, yet re-appeared once column of smoke in the same general area, and weather, fuels, and topography aligned to with this new sighting, fi re crews were able permit more obvious combustion. to fi nd the fi re and begin suppression actions. By the time they arrived on scene, the fi re was Tunis Ridge Fire —June 1943, 1.6 ha (4 ac). approximately 26 ha (65 ac) and was contained The fi re began on June 8, was fi rst reported on later that evening. As fi re crews were returning June 9, and, “Warden Ogle hunted for it on that to mop-up the fi re on the morning of the 20th, day and again on June 10th; but light rains had “a snag fell and slid down the mountainside damped it down and as no smoke was visible beyond the control line” igniting a dense laurel he did not fi nd the fi re…. Fire was corralled thicket. It was several more hours before the at 2:00 am on June 12, but kept breaking over fi re was fi nally controlled. Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 75
Ellis Butt Fire—July 1968, 2 ha (5 ac). The WFU fi re in the park burned in mesic, old- fi re started in a lightning-struck pine. When growth, oak-dominated communities and crews arrived it was burning in deep duff (5 generally stopped upon reaching tulip poplar cm to 10 cm). The fi re was originally called (Liriodendron tulipifera) and red maple (Acer controlled at 7:30 PM on July 17 at 0.6 ha (1.5 rubrum) dominated communities. Fire burned ac), but at 10:00 AM on July 18, the fi re “had predominantly through the litter layer and broken out along the line at all points except persisted through downed logs and stump holes. the top.” Heavy rain early on July 19 helped Along the west fl ank of the fi re there were fi refi ghters secure the perimeter, though there short up-slope head fi res in shrub-dominated were still tree stumps and standing dead trees communities, with scorch heights of up to burning in the interior of the fi re. 2 m (6.6 ft) on the mountain laurel (Kalmia latifolia). The fi re area received light rain on Unsuppressed Lightning Fires April 9, 1.3 cm (0.5 in) of snow on April 10, >40.5 ha (100 ac) and several centimeters of rain from April 18 to 20. The majority of fi re growth occurred in the Five of the reports for unsuppressed fi res fi rst three days of the fi re. By April 13, there were selected for their insights about fi re was no growth in fi re size although smoldering behavior. All of these burned for longer than a continued within the burn. week and grew to at least 40.5 ha. Collins II Fire—April 20 to 28, 1999, 52.6 Polecat Ridge Fire—July 27 to August ha (130 ac). The fi re was discovered on April 18, 1976, 44.5 ha (110 ac). The 1976 Polecat 21 and by evening had grown to approximately Ridge fi re ignited on July 27, and was reported 12 ha (30 ac). It burned from oak-dominated and located on July 28. This fi re was the fi rst ridgetop communities downslope into mesic experimental attempt by GSMNP to implement coves, carrying through leaf litter and persisting what is now known as WFU. On discovery, in downed logs. It burned across moist the fi re was approximately 1.2 ha (3 ac) on drainages. This was largely a backing fi re with the top of the ridge in a stand dominated by little duff consumed, though higher intensities pines (Pinus pungens, P. rigida, P. virginiana, and severities were observed along ridgetops. and P. echinata). The fi re smoldered and crept The majority of fi re growth took place from downslope into a pine-hardwood mix and by April 21 to 22, when the daily minimum July 31 appeared to have been extinguished relative humidity dropped to nearly 30 percent. by rain. No smoke was visible on August 1. The fi re received little direct sunlight on April On August 2, the fi re began a run that lasted 23, minimum relative humidity between 40 through August 5, growing to its maximum percent and 50 percent, and light rain (reported size of 44.5 ha (110 ac) and stopping at a trail as one millimeter at the nearest weather station) on the south side. The fi re persisted in the that evening. Drainages coincided with the interior, continuing to smolder in downed logs majority of the fi re perimeter. A wild boar (Sus and standing dead trees. The fi re received scrofa) rooting site stopped fi re growth along 1.3 cm (0.5 in) of rain from August 6 to 7 and a portion of the northern fi re perimeter. The 1.8 cm (0.7 in) of rain on August 16, and was fi re was notable for top-killing rhododendron declared out on August 18. (Rhododendron maximum) and mountain laurel during the major period of fi re growth. Forney Ridge Fire—April 6 to 27, This fi re took place during the height of spring 1998, 149.7 ha (370 ac). The fi rst offi cial wildfl ower season. Park fi re and natural Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 76
resource specialists were surprised that the fi re to smolder and creep in its interior for several behavior and effects were as severe as they weeks. The last smoke was observed on May were in light of the seasonally moist live fuels. 18 and the fi re was offi cially declared out on July 4. Blacksmith Fire—August 19 to September 22, 1999; 211.7 ha (523 ac). Part of the area DISCUSSION of the Blacksmith fi re had burned previously in 1988. Most of the Blacksmith Fire burned with The case studies illustrate how fi re a low intensity, backing fi re. Small, sporadic behavior varies according to seasonal and headfi re runs occurred in small patches, mostly weather conditions and give a broader context in pine regeneration areas that resulted from for interpreting the past decade of wildland the 1988 fi re. Eighty-two percent of the fi re fi re use. While lightning-caused fi res often growth occurred between August 29 and begin during a rain event, they may persist in September 6. A series of dry cold fronts came a live or dead tree for enough time to allow through the unit from August 24 to 27. The surrounding fuels to dry suffi ciently for relative humidity was variable throughout eventual fi re spread. Fire may reach surface the duration of the fi re. There were sporadic fuels in a variety of ways: through portions of drops of relative humidity below 20 percent, the burning trunk falling to the ground, a wind but during the majority of the fi re growth the that scatters embers into available fuels, or a relative humidity remained between 40 percent tree that burns entirely to the ground. and 50 percent. Fuels were atypically dry; Large fi re growth is sporadic, occurring consumption was noted in litter, duff, and root when forest fuel conditions align with systems. topographic and weather conditions conducive to fi re spread. For example, the major growth Chilly Springs Knob Fire—April 3 to July for the 1999 Blacksmith Fire occurred while 4, 2006; 369.5 ha (913 ac). The fi re was the relative humidity remained in the 40s and ignited by lightning on April 3 in an oak-pine included perimeter expansion spanning both (Quercus-Pinus) community in the western day and night. Fuels had been drying for portion of the park. The fi re did not produce several days prior to this growth period as a much smoke or exhibit noticeable growth cold front passed over the area. As the relative until April 5 when fi re size was estimated at humidity rose, the fi re smoldered and crept about 16 ha (40 ac) by midday. By April 6, it until it reached a more receptive fuel bed in had grown to approximately 121 ha (300 ac). terms of composition (pine needles, oak leaves, The fi re received 2.5 cm (1 in) of rain early pine seedlings, and saplings) and condition in the morning of April 8. On April 10, the (dry and combustible). This growth pattern is fi re perimeter had grown to 230 ha (569 ac). typical of prolonged unsuppressed fi re events There were two more major periods of fi re observed in this park and in other areas of the growth and by April 18 the fi re had reached U.S. (Despain 1983). The majority of the fi re its fi nal size of 370 ha (913 ac). Fire spread growth occurs within a fraction of the overall to the west was impeded by roads and creeks fi re duration. Of the fi ve unsuppressed fi re along the southern and southeastern edges. events that grew to over 40.5 ha (100 ac), the Along the northern perimeter, the fi re stopped majority of fi re growth occurred in just under at unreceptive fuels and a small portion was 20 % of the total burning days. The actual stopped where fuel continuity was disrupted by start of the major growth period was highly European wild boar rooting. The fi re continued variable, beginning on the fi rst or second day Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 77
after the lightning strike on three fi res, seven forest fl oors, exposing soil that precludes fi re days after ignition on the Polecat Ridge Fire, spread. Disturbed sites have been recorded at and 11 days after ignition on the Blacksmith all elevation ranges and most vegetation types Fire. (Bratton et al. 1982). Disturbed forest-fl oor Extinguishment of unsuppressed fi res patches in excess of 500 m2 (1,235 ft2) have occurs as a result of the sensitive relationship been recorded (Howe and Bratton 1976). These among fi re behavior, weather, topographic disturbances stopped fi re growth on portions of features, and fuel availability. Extinguishment both the Collins II and Chilly Springs fi res. may also result from a variety of ecological The effects of rooting practices of the factors, such as changes in vegetation (fuel introduced European wild boar are a unique types), weather (a rain event), or the physical twist on fi re-fl oral-faunal relationships and environment (e.g., moist sites unfavorable to would make a useful addition to extant studies fi re spread). Wet to moist coves, stream beds, on boar in the park (Howe and Bratton 1976, drainages, and depressions formed the most Bratton et al. 1982). The relationship between common boundaries for the observed fi res fi re effects and boar disturbance, correlating that were allowed to progress until “natural” likely rooting sites with potential fi re spread, extinction. Anthropogenic disruptions of fuel and the effects of boar on post-fi re forest continuity, such as trails, roads, or historic regeneration are some areas of potential land-use patterns, can also impede fi re growth. interest. Future research in this area would be The characteristics of these boundaries useful in planning efforts, both in terms of fi re (e.g., width, fuel type, topography), again planning and prioritizing focus areas for the combined with weather and fuel conditions, park’s boar management program. In terms dictate their effectiveness. For instance, a trail of fi re regimes and fi re behavior, the specifi c was effective in stopping the 1976 Polecat effects of rooting may not be as important as Ridge Fire. In contrast, an unimproved and the sensitive relationship between fi re spread unmaintained road did not stop the Forney and ambient conditions. As the case studies Ridge Fire. Vegetation-based controls on fuel show, even small breaks in fuel continuity can continuity and availability have also limited alter fi re behavior and retard fi re growth. fi re spread. Studies have suggested that leaf With a larger dataset from unsuppressed litter of pyrogenic species (e.g., oak) are more lightning-caused fi res, a study examining the conducive to fi re spread than the leaf litter of attributes of fi re barriers (e.g., aspect, slope, fi re-sensitive, shade-intolerant species such as topography, changes in vegetation type) would red maple (Abrams 2006). This phenomenon be useful in identifying future prescribed burn has been observed in the park, especially on boundaries and defi ning trigger points on the Forney Creek and Chilly Springs Fires. WFU fi res and wildfi res. A comparison of the Another interesting phenomenon has been effectiveness of these barriers under different the infl uence of non-native species on fi re fuel, weather, and seasonal conditions to behavior, in particular the European wild boar. highlight likeliness for fi re growth would also Boars were introduced into a North Carolina be useful in a variety of fi re planning efforts. preserve near the western edge of the park as a Further, understanding the effects of changing game species in the early 1900s. They escaped ecosystems (e.g., change to shade-tolerant their preserve and fi rst entered the Great species or prevalence of European wild boar) Smoky Mountains in the 1940s. Through their relative to fi re behavior and growth would be rooting for underground plant parts and buried helpful in prioritizing management efforts and acorns and nuts, boar extensively disturb defi ning target conditions. Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 78
A combination of weather factors, including objectives and human-made barriers (e.g., relative humidity, wind, precipitation, and cloud Calderwood and Chilhowee Lakes), this is no cover, has been the most commonly observed longer likely to occur. determinant of fi re growth or extinguishment Frequency of lightning-caused fi res has for unsuppressed lightning-caused fi res greater varied throughout the park’s history (Figure 2). than 25 ha (100 ac). Three of the fi ve large Changes in suppression tactics have affected unsuppressed fi res (Polecat Ridge, Forney fi re size and duration for the period of this Creek, and Collins II) had two or more study. In 1962, air tankers were used in the precipitation events that contributed to ending park for the fi rst time, enhancing wildland fi re the fi res. In all fi ve fi res, the major periods of suppression efforts. In the Chestnut Ridge growth coincided with days of little to no cloud Fire report for that year, District Ranger cover, which probably contributed to increased Norman Roy noted, “It is estimated that [80.9 insolation, daytime heating, and drying. These ha] 200 acres would have burned, instead of growth periods also corresponded with relative [28.9 ha] 71.52, if we had not had the aid of humidities below 50 %, although more research the air tanker.” On the other hand, burnout is needed to discern the absolute cause-effect operations—the process of securing fi re relationship between fi re spread and relative perimeter by setting a back fi re from a strategic humidity. location to consume available fuels—that Instances where lightning-caused fi re has could increase fi nal total area burned, were not crowned or spotted have not been reported a regular part of suppression efforts up until previously in the region (Barden and Woods the mid-1980s. The fi rst mention of burnout 1973, Harrod and White 1999). These GSMNP operations on a suppressed lightning fi re was case studies provide two clear examples of in the fi re report for the 1987 Slaty Fire, which high-intensity fi re behavior. In portions of the covered 36.4 ha (90 ac). As noted in the results Forney Ridge Fire (<20 % of the total burned section, the only suppressed lightning fi re area), short yet intense up-slope headfi re that grew to over 40.5 ha (100 ac), the 1988 runs occurred through patches of mountain Redman Fire, had an unknown portion of the laurel. During the main period of growth on fi nal perimeter result from burnout operations. the Blacksmith fi re, an intensive uphill run Discrepancies in fi re reporting data consumed a stand of pine saplings that recruited contribute to uncertainty in the calculation of from a prior fi re (1988 Shop Creek). fi re duration. The offi cial start date is often There are wide ranges of variables that when smoke was fi rst reported rather than the contribute to fi re growth, behavior, and effects. day of lightning ignition. This could lead to In addition to some of the factors discussed an underestimation of fi re duration throughout above, there are many that may never be the suppression era. For this study, fi re start viably assessed. Landscape fragmentation dates taken from fi re reports or summary tables at a large scale is one example. Regional were in most instances verifi ed to refl ect the fi re history studies refl ect a higher yearly date of the lightning strike using information average number of lightning-caused fi res on reported by lookout tower operators. At times, the Cherokee National Forest, located at the especially from the mid 1980s on, it appears park’s southwestern boundary (Barden and that fi re declared-out dates were several days Woods 1973, Cohen and Dellinger 2006). At or weeks after fi res last exhibited any activity one time, it may have been possible for fi res (smoke or heat). Considering the history of to start in this area and progress into what is fi res emerging from apparent dormancy and now GSMNP. Due to different management exhibiting aggressive fi re behavior several Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 79
days after appearing (see case studies, above), exploration of this information would provide this is a prudent policy. However, it is likely better understanding of historic fi re regimes, that the mean fi re duration date for suppressed fi re-vegetation-site relations, and the different fi res would be reduced if the correct date of approaches available for comprehensive the last observed smoke was consistently ecosystem management. available. Correct ending dates would reduce the mean fi re duration for the 1980s and 1990s CONCLUSIONS (Table 1). This study focused on fi res originating Though the unsuppressed-fi re dataset is within the park boundary and area burned small, these case studies highlight several key within the park. When verifying extant report points that begin to defi ne the role of lightning- data against the published fi re history for caused fi re and fi re regimes in the southern the park (Harmon 1981), it became evident Appalachians. First, unsuppressed lightning- that because of missing fi re reports, it is not caused fi res persist for longer periods of time possible to assert that all fi res used in this study and burn over larger portions of the landscape started inside the park or that the area burned than suppressed lightning-caused fi res. This was wholly within it. Discrepancies between is important for understanding the impacts the fi re history study and extant data apply to of lightning-caused fi res on eastern forests. an undetermined four of 80 suppressed fi res Second, the potential for fi re growth may not be from 1940 to 1979 used in this study (Harmon directly related to weather and fuel conditions 1981). at the time of ignition. Lightning-caused fi res Continued study on the distribution and can start during precipitation events and can spread of fi res in terms of weather, vegetation, persist through these wet periods, becoming the physical environment, previous natural active only at a later date when adjacent fuels events, and human-caused disturbances have dried. Third, not all ignitions will result will further our knowledge of the role of in large fi res. To date, the size of unsuppressed fi re in these forests. Specifi cally, research lightning-caused fi res has been evenly split on the links between climate variables and between fi res <0.1 ha (0.25 ac) and >40.5 ha fi re growth would assist in management of (100 ac). lightning-caused fi res and test the hypothesis The GSMNP monitoring programs and that lightning-caused fi res have increased in careful collection and storage of fi re data signifi cance during periods of drought (Lafon et during the two fi re management eras made this al. 2005, Peterson and Drewa 2006). Lightning- study possible. The park’s ongoing research caused fi res tend to occur in the growing season partnerships and long-term monitoring while prescribed fi res are usually ignited in programs provide rich baseline ecosystem the dormant season. Data collected from the information and will enable a variety of in- WFU program will enable the comparison of depth studies in the future. The park’s WFU fi re effects and seasonality using burn severity program is unique in that all of the fi res in this maps (Key and Benson 2005), GSMNP’s long- study had no suppression actions taken on the term vegetative monitoring data, and data from fi re perimeter. This study not only emphasizes the park’s prescribed fi re effects monitoring the benefi ts of such a program and data, but the program. Fire behavior data from lightning- importance of continuing to collect long-term, caused fi res can be used to calibrate fi re high quality fi re behavior and associated data modeling software. Ultimately, any further whenever possible. Fire Ecology Special Issue Cohen et al.: Patterns in Lightning-caused Fires Vol. 3, No. 2, 2007 Page 80
ACKNOWLEDGMENTS
The authors would like to thank Leon Konz, Rhonda Watson, Annette Hartigan, Paul Reeberg, Erin Woodard, Caroline Noble, Tim Sexton, and the staff at Great Smoky Mountains National Park, past and present, for their help with this study and their continued support of progressive fi re management in the park. We would also like to thank Carol Miller and the two anonymous reviewers for their insight and suggestions that greatly improved this manuscript.
LITERATURE CITED
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