John Long

Landscape Changes in Yellowstone: Results from the Fan Fire of 1988

John A. LongMontana State University

Bozeman, MT 59717

December 2, 2011Word Count: 3252

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Abstract

Fire is an integral part of fire-adapted ecosystems, yet it represents a major disturbance to the landscape. For vegetative communities, a major wildfire often results in losses of habitat and core area, increases in fragmentation, and potential decreases in species richness. The 1988 fires in Yellowstone National Park were among the largest in recorded history, burning more than one-third of the park and substantial portions of the surrounding area. The broad goal of this paper is to examine wildfire-induced changes in the landscape and the accompanying effects on vegetation structure resulting from the 1988 fires at a detailed level. Therefore, this paper is restricted to a single fire, the Fan Fire. It was one of the earliest in the 1988 fire season and was entirely contained within Yellowstone National Park. Specifically, this paper seeks to: (1) identify changes between pre-fire and post-fire land cover types within the Fan Fire perimeter; and (2) quantify those changes using landscape metrics. Results indicate that the Fan Fire induced changes in the landscape. Evidence was found for increased fragmentation and a loss of core area; however, forest diversity did not suffer. In general, species present before the fire were present after the fire. Specifically, there were increases in the amount of lodgepole pine, decreases in the amount of Englemann spruce, and minor changes in whitebark pine, Douglas fir, and non-forested areas.

Keywords: Fan Fire, fires of 1988, wildfire, fragmentation, land cover type change, Yellowstone National Park.

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Introduction

Fire is an integral part of many ecosystems. Although the aftermath of a major wildfire appears destructive, fire plays a constructive role in ecosystem health. For fire-dependent ecosystems, fire is not only beneficial, it is essential. These ecosystems have evolved with fire as a natural component that facilitates the maintenance of an ecosystem’s characteristic structure and composition. One of the more familiar fire-dependent ecosystems is the lodgepole pine and associated communities of the Rocky Mountains, such as those that comprise the Greater Yellowstone Ecosystem (GYE).

In the summer of 1988, Yellowstone National Park (YNP) experienced one the worst fire seasons in recorded history, eventually forcing the National Park Service to close YNP to the public for the first time since the park’s establishment. By the end of the summer, a total of 248 fires had started in the GYE, including 16 major fires. Of YNP’s nearly 9000 km2, approximately 4856 km2 were scorched and 3209 km2 were burned (National Park Service, 2010). Fire is a dominant and recurring factor in the forests of the Rocky Mountains. The 1988 fires in the GYE were not unique to the area; large fires have occurred repeatedly in the region’s dry coniferous forests. Recent estimates indicate that large fires in the area are on a 175-350 year cycle (Baker, 2009) and represent a major disturbance to the ecosystem.

Major disturbances, such as the 1988 Yellowstone fires, alter the landscape in various ways. Consequently, wildfire plays a critical role in shaping vegetation community structure. Following a wildfire, an ecosystem rebounds via secondary succession; the pre-fire vegetative structure is altered as the biotic legacies of fire-adapted species and the migration of pioneer species recolonize the area. As community structure includes both species richness and species distribution (Reice, 1994), landscape measures are important tools for examining the response of vegetation communities to major disturbances.

The goal of this paper is to examine wildfire-induced changes in the landscape and the accompanying effects on vegetation structure resulting from the 1988 fires in the GYE. Since this is a far-reaching goal, this paper restricts the scope to the Fan Fire. The Fan Fire was one of the earliest fires, beginning on June 26, and it was not fully extinguished until August 23, 1988. By then, it had burned 11,069 hectares in the north-west corner of the park, a “small” fire in comparison to the major fires such as the North Fork Fire which burned 214,969 hectares (Rothermel et al., 1994). Specifically, this paper seeks to: (1) identify changes between pre-fire and post-fire land cover types within the perimeter of the Fan Fire; and (2) quantify changes within the perimeter of the Fan Fire in terms of landscape metrics. Study Region

The study region was YNP, which is located near the center of the GYE (Figure 1). The Fan Fire was located in the extreme northwest corner of the park (Figure 2).

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In general, the pre-fire study region was dominated by large areas of lodgepole pine, interspersed with whitebark pine and Englemann spruce at higher elevations, and Douglas-fir at lower elevations. Patches of aspen and sizeable areas of grassland also occur. This general pattern was also valid within the perimeter of the Fan Fire except that there are no areas of aspen.Methods

Several GIS layers were obtained from the YNP Spatial Analysis Center: national park boundaries, fire start points, fire perimeters, burn types, pre-fire cover type and post-fire cover type. In addition, a 1 arc-second (30 m) digital elevation model (DEM) was obtained from the United States Geological Survey's National Elevation Dataset. The national park boundaries layer contains all national parks and was clipped to Yellowstone and Grand Teton National Parks. The fire start points layer contains the ignition points for 22 major fires. The locations of the ignition points are accurate within 100 m and were determined by the observations of fire lookouts. The fire perimeter layer depicts the maximum areal extent for the 22 major fires and was determined by integrating several sources such as daily infrared photography flights, satellite imagery, and ground-based reconnaissance. Due to the possibility of unburned areas within the perimeter, the fire perimeter likely over-estimates the actual area burned.

The burn type layer categorizes the character of burned areas with a 5-acre resolution. Burn types are: canopy burn, mixed burn, non-forested burn, undifferentiated burn, and unburned. A canopy burn indicates that the forest overstory and ground cover were burned; a mixed burn describes areas characterized by a combination of unburned, scorched or blackened trees as well as burned ground cover; a non-forested burn describes burned ground cover; and undifferentiated burns are burned areas that could not be reliably placed in one of the other burn categories.

The pre-fire cover type layer describes the forested cover types from before the 1988 fires. The land cover types were assigned by examining aerial photographs and ground truth transects. There were 40 land cover types in the GIS layer; however, these were collapsed into 9 general categories based on species: lodgepole pine, whitebark pine, Douglas fir, non-forested, Englemann spruce, aspen, mixed conifer, krumholz, and water. The post-fire cover type layer was created in 1991 by modifying the pre-fire layer to reflect changes in land cover type following the fires.

Mapping areas with post-fire land cover types that differed from the pre-fire land cover types was a multistep process. First, a map of areas that changed land cover types within the Fan Fire perimeter (Figure 3) was created by using the non-zero outputs from a spatial model in ArcMap (post-fire cover type code — pre-fire cover type code). When the pre-fire and post-fire cover types were the same, the output was a zero; similarly, non-zero outputs indicated a change in land cover type. Next, a more explicit map (Figure 4) was made of the changed areas in terms of specific transitions (e.g., Englemann spruce to lodgepole pine). The process was

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the same as with the general map except that the post-fire cover type codes were multiplied by ten (10*post-fire cover type code — pre-fire cover type code); therefore; upon subtraction, each possible transition had a unique code, which allowed the mapping of specific changes. Finally, landscape and class level (land cover type) metrics were computed for the area within the Fan Fire perimeter using the landscape analysis tool V-LATE 2.0, an ArcGIS extension. Results

The Fan Fire Perimeter encompassed 110,682,918 m² (≈ 11,068 ha) and approximately 1338 ha (12.09%) of that area experienced changes in land cover type. Pre-fire land cover types consisted of six of the nine possible land cover types within YNP: water, lodgepole pine (Pinus contorta), whitebark pine (Pinus albicaulis), Douglas fir (Pseudotsuga menziesii), non-forest, and Englemann Spruce (Picea engelmannii). Aspen, mixed conifer and krumholz were not present within the confines of the Fan Fire perimeter. The post-fire land cover types were the same as for the pre-fire land cover types; hence, there was no change in richness as a result of the Fan Fire.

Specific land cover changes are represented as a change matrix (Table 1) and as a percent of the changed area (Table 2). There were a total of 16 of the 30 possible land cover transitions realized; however, over 95% of the area that changed land cover type was a result of three distinct transitions. The overwhelming majority (91.93%) of transitions were Englemann spruce to lodgepole pine, while Englemann spruce to non-forested accounted for 2.04% and non-forested to lodgepole pine accounted for 1.06%. The other 13 transitions were less than 0.50% each and are likely artifacts of the raster to polygon conversion process since they are typically single pixels located along the edges of a land cover type. Most of the land cover changes took place in the eastern third of the Fan Fire perimeter, where the majority of the Englemann spruce was prior to the fire.

At the landscape level, there is evidence for an increase in fragmentation, loss in core area, and a loss of diversity as a result of the Fan Fire (landscape metrics are summarized in Table 3). The increase in fragmentation is supported by several metrics: (1) an increase in the number of patches (NP); (2) an increase in total edge (TE); (3) a decrease in mean patch edge (MPE); (4) a slight increase in the mean shape index (MSI); and (5) a decrease in the mean perimeter-area ratio (MPAR). The loss of core area is supported by: (1) a decrease in total core area (TCA); (2) and increase in cority; and (3) a decrease in core area index (CAI). Finally, evidence for a loss of diversity comes from: (1) a decrease in Shannon’s Diversity Index; (2) a decrease in Shannon’s Evenness Index; and (3) and an increase in dominance.

Analysis at the class-level for lodgepole pine indicated that the class proportion had increased from 62.6% to 73.7% of the area within the Fan Fire perimeter. This was accompanied by an increase in the number of core areas (NCA) and a 17.7% increase in core area (CA). On the other hand, lodgepole pine showed an increase in landscape fragmentation as evidenced by increases in NP, NCA, and

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TE, and decreases in mean patch size (MPS) and MPE. Practically all of the gains made by lodgepole pine came at the expense of Englemann spruce as the vast majority (97.2%) of the area lost by Englemann spruce transitioned to lodgepole pine. The class proportion of Englemann spruce dropped from 20.1% of the area before the fire to 8.9% in the post-fire landscape. In addition, Englemann spruce lost more than half of its core area and what remained became significantly more fragmented. Details for class-level metrics are summarized in Table 4.

Using similar lines of evidence from class-level metrics for the other classes produced the following results. Whitebark pine had a negligible change (0.1%) in class proportion, with a slight loss in core area (1.3%) that was accompanied by a decrease in fragmentation. This is the opposite pattern to that of lodgepole pine. Non-forested areas increased slightly (0.25%) in class proportion and gained 2.6% in core area; however, this class also experienced large decreases in fragmentation. Areas of Douglas fir and water encountered essentially no change as measured by any of the class-metrics; this is also evident by examining the change matrices (Tables 1 & 2).Discussion

The Fan Fire altered the region. The overall effect was a more fragmented landscape with an accompanying loss in core area, which is in complete agreement with what would be expected from a major disturbance under current theories. The fact that more than 95% of the area that changed land cover type resulted from three distinct transitions makes sense in the context of the fire-adaptability of the species involved. Ecological succession following a major disturbance may proceed along several different trajectories. The initial biological response to disturbance is in reaction to the mechanism of the disturbance (Dale et al., 2005). In the 1988 fires, the primary mechanism was heat. In the Fan Fire, the initial biological response came from the survivors, organisms that lived through the fire, as well as the biotic legacies such as seeds and regenerative vegetation. The initial stages of secondary succession are strongly influenced by the persistence and growth of survivors (Dale et al., 2005), as well as recruitment and immigration of mobile organisms.

The forests of the GYE are uniquely adapted for post-fire survival. Lodgepole pines have deep tap roots, insulated from the intense heat, while some trees employ serotinous cones. Serotiny is a strategy that favors survivorship since serotinous cones allow for maximum seed dissemination immediately after a fire, when the availability of resources is high and inter-species competition is low (Aber & Melillo, 2001). However, serotiny is not ubiquitous in lodgepole pine; it is dependent on elevation and age of the tree. In the GYE, serotiny varies noticeably; it is relatively low for trees above 2400 m and for young trees below 2400 m. Thus, serotiny is most prevalent in older lodgepole pines below 2400 m (Schoennagel, 2006). The region within the Fan Fire ranges from 1350 to 4200 m in elevation with an approximately even split between elevations below and above 2400 m. Serotinous and non-serotinous trees often coexist with relative proportions

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dependent on the nature and timing of the last disturbance by fire (Knight & Wallace, 1989). Since fire suppression was park policy in Yellowstone for the majority of the twentieth-century, it is not surprising that serotiny is less common in younger trees (< 75 years).

Within the Fan Fire perimeter, lodgepole pine has been very successful at reestablishing areas that were lodgepole pine prior to the fire, as well as colonizing substantial areas that were previously Englemann spruce. As seen in the results, the overwhelming majority (91.93%) of transitions in land cover type were Englemann spruce to lodgepole pine, while Englemann spruce to non-forested areas accounted for 2.04% and non-forested to lodgepole pine accounted for 1.06%. Thus, the key observation here is the superiority of lodgepole pine in secondary succession versus the inability of Englemann spruce to compete; both are direct results of the fire-adaptive nature of lodgepole pine and of the fire sensitivity of Englemann spruce.

The relatively small changes in area, in comparison to lodgepole pine, for the other classes are a result of species-specific adaption and strategies to increase post-fire survivorship. The whitebark pine, a high elevation specialist and a vital food resource for grizzly bears in the region, utilizes a soil seed-bank strategy in which seeds are cached underground by foraging birds and squirrels. Seeds may, depending on the depth of burial, survive an intense fire. In contrast, Douglas fir typically grows at lower elevations where the fires were less intense and they were aided by a thick insulating bark that helped many to survive. In addition, about three quarters of the shrubs, forbs, and graminoids present before the fire resprouted readily (Baker, 2009) and were seen as early as the following spring (Turner, 2009).

The Fan Fire illustrates that land cover type and the pre-fire biomass contribute to the regrowth potential of vegetation. For example, areas with high pre-fire concentrations of lodgepole pine were likely to have high post-fire concentrations of lodgepole pine because: (1) the environment continues to favor the species; (2) areas with high pre-fire biomass left more biotic legacies; and (3) biotic legacies (e.g., serotinous cones) are superbly adapted to recolonize a burned area. Similar cases can be made for Douglas fir, whitebark pine, and the non-forested areas. The only exception is Englemann spruce which is fire sensitive due to its thin bark, shallow roots, and moderately flammable foliage (United States Forest Service, 2011). For the Fan Fire, burn severity, or fire intensity (see Figure 5), had very little effect on regrowth across different land cover types, which is not surprising since the GYE is a fire-adapted ecosystem.

Although ecological interactions are complex, many post-fire responses were expected. For example, lodgepole pine reestablishment was abundant and the sapling density was the greatest at lower elevations, facts consistent with trends in serotiny (Turner, 2009). On the other hand, post-fire succession following the 1988 fires produced a few surprises, at least to some experts. For example, native plant cover was rapidly restored by natural processes, which was contrary to at least two notions. First, some thought that succession would be slow (see e.g., Turner, 2009)

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and dependent on long distance dispersal from unburned areas. Secondly, it was expected that non-native plants would invade the burned areas, but in fact they only managed to establish themselves in less than 3% of the burned areas in the GYE, usually along roadways (Turner, 2009). Indeed, the post-fire ecosystems are essentially the same as those that prospered before the flames (Paine et al., 1998). While these comments refer to the burned areas of the GYE as a whole, they hold equally well for the Fan Fire perimeter. The major landscape alterations in terms of land cover types: increased lodgepole pine, decreased Englemann spruce, and relatively minor changes in whitebark pine, Douglas fir, and non-forested areas, support the concept of the resilience of a fire-adapted ecosystem and the importance of biotic legacies. However, conclusions based on changes in land cover should be interpreted cautiously because the post-fire land cover map was created by modifying the pre-fire map; therefore, there is a potential bias toward not changing cover types. Recognizing the potential for bias, the following observation is noted. With the single exception of the inverse relationship between areas of lodgepole pine and Englemann spruce, pre-fire and post-fire land cover types showed very little change; species that were present pre-fire were by and large the ones that recolonized the area post-fire.

References

Aber, J. & Melillo, J. (2001). Terrestrial ecosystems (2nd ed.). San Diego: Academic Press.Baker, W. (2009). Fire ecology in Rocky Mountain landscapes. Washington, D.C.: Island Press.Dale, V., Swanson, F., & Crisafulli, C. (2005). Disturbance, survival, and succession:

Understanding ecological responses to the 1980 eruption of Mount St. Helens. In V. Dale, F. Swanson, & C. Crisafulli (Eds.), Ecological response to the 1980 eruption of Mount St. Helens (pp. 3-12). New York: Springer.

Knight, D. & Wallace, L. (1989). The Yellowstone fires: Issues in landscape ecology. BioScience, 39(10), 700-706.

National Park Service. (2010). Wildland fire in Yellowstone. Available Online: http://www.nps.gov/yell/naturescience/wildlandfire.htm

Paine, R., Tegner, M., & Johnson, E. (1998). Compounded perturbations yield ecological surprises. Ecosystems, 1(6), 535-545.

Rothermel, R., Hartford, R., Chase, C. (1994). Fire growth maps for the 1988 Greater Yellowstone Area fires. Gen. Tech. Rep. INT-204. Ogden, UT: US Department of Agriculture, Forest Service, Intermountain Research Station.

Schoennagel, T., Turner, M. & Romme, W. (2003). The influence of fire interval and serotiny on Postfire lodgepole pine density in Yellowstone National Park. Ecology, 84(11), 2967-2978.

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Turner, M. (2009). Ecological effects of the ’88 Yellowstone fires. Yellowstone Science, 17(2), 24-30.

United States Forest Service (USFS). (2011). Fire effects information system. Available online: http://www.fs.fed.us/database/feis/.

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Table 1Change Matrix: Number of Pixels Changing Land Cover Type

ToW LP WB DF NF ES

From

W 10 4 0 0 9 0LP 0 35705 14 8 65 43WB 0 42 3605 0 34 34DF 0 29 0 642 0 0NF 0 73 8 0 5371 14ES 0 6357 40 0 141 4964

Key: W = water, LP = lodgepole pine, WB = whitebark pine, DF = Douglas fir, NF = non-forested, ES = Englemann Spruce. Total pixels = 57,212.

Table 2Land Cover Types Changes as a Percent of the Total Number of Changed Pixels

ToW LP WB DF NF ES

From

W - 0.0529 - - 0.1191 -LP - - 0.1853 0.1059 0.8601 0.5690WB - 0.5558 - - 0.4499 0.4499DF - 0.3838 - 8.4954 - -NF - 0.9660 0.1059 - - 0.1853ES - 84.1207 0.5293 - 1.8658 -

Table 3Landscape Level Metrics

Metric Pre-Fire Post-FireArea* Total Area (TA) 110682918.32 110682918.32

Number of Patches (NP) 103 113Core Area** Total Core Area (TCA) 105762970.9 105604108.4

Core Area Index (CAI) 95.55 95.41Diversity Richness 6 6

Shannon's Diversity 1.073 0.897Shannon's Evenness 0.599 0.501Dominance 0.719 0.895

Edge* Total Edge (TE) 499955.42 516804.87Mean Patch Edge (MPE) 4853.94 4573.49

Form Mean Shape Index (MSI) 1.666 1.699Mean Perimeter-Area Ratio (MPAR) 0.026 0.022

*All areas are in square meters and lengths are in meters. **Core area distance = 10 m

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Table 4Class Level Metrics

Water Lodgepole Pine Whitebark PineMetric Pre-fire Post-fire Pre-fire Post-fire Pre-fire Post-fire

Area* NP 2 1 8 11 16 15MPS 21999.9 22436.9

8665885.97 7415979

450555.54 474005.55

PSSD 2531.47 016063103

.2221425671

.46505280.8

5 504551.7Core Area**

NCA 2 1 17 19 18 17CA 43999.9 22436.9

69327087.72

81575769.03

7208888.72

7110083.22

TCCA 32844.8 16388.667609632

.7679477669

.576658310.

826571927.

58CAI 74.65 73.04 97.52 97.43 92.36 92.43

Diversity Proportion

0.04 0.02 62.64 73.7 6.51 6.42Edge TE 1194.21 652.23

172116.64

210666.74 55975.18 54745.2

MPE 597.11 652.23 21514.58 19151.52 3498.45 3649.68Form MSI 1.136 1.228 2.209 2.031 1.637 1.641

MPAR 0.027 0.029 0.021 0.021 0.018 0.012

Douglas Fir Non-forest Englemann SprucePre-fire Post-fire Pre-fire Post-fire Pre-fire Post-fire

Area* NP 10 10 40 31 27 45MPS 128291.3

7 126084.48265149.7

2351078.5

5 822742.2 218452.2PSSD 98130.07 98647.16

629233.23

704690.53

3274177.3 513929.23

Core Area**

NCA 10 10 51 42 41 55CA 1282913.

681260844.

8210605988

.8710883435

.14 22214039 9830349.2TCCA 1134293.

641113898.

779376260.

379687400.

85 209516298736823.

03CAI 88.42 88.35 88.41 89.01 94.32 88.88

Diversity Proportion

1.16 1.14 9.58 9.83 20.07 8.88Edge TE 15278.32 15108.83

126589.57

122719.89 128801.5 112911.99

MPE 1527.83 1510.88 3164.74 3958.71 4770.43 2509.16Form MSI 1.259 1.257 1.726 1.812 1.623 1.668

MPAR 0.015 0.015 0.029 0.02 0.032 0.029

*All areas are in square meters and lengths are in meters. **Core area distance = 10 m

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Figure 1.Map of the Greater Yellowstone Ecosystem

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Figure 2.Map of the 1988 Yellowstone Fire Perimeters

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Figure 3.Map of the Pre-fire and Post-fire Cover Types, and Land Cover Changes within the Fan Fire Perimeter

Figure 4.Map of Specific Land Cover Type Changes within the Fan Fire Perimeter

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Figure 5.Map of Burn Types

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