John Long
Landscape Changes in Yellowstone:
Results from the Fan Fire of 1988
John A. Long
Montana State University
Bozeman, MT 59717
December 2, 2011
Word Count: 3252
1
John Long
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.
2
John Long
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). In general, the prefire 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
3
John Long
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 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.
4
John Long
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 nonforested 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 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.
5
John Long
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 interspecies 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 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
6
John Long
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) 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 prefire 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
7
John Long
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.
Turner, M. (2009). Ecological effects of the ’88 Yellowstone fires. Yellowstone Science, 17(2), 2430.
United States Forest Service (USFS). (2011). Fire effects information system. Available online:
http://www.fs.fed.us/database/feis/.
8
John Long
Table 1
Change Matrix: Number of Pixels Changing Land Cover Type
To
W
10
0
0
0
0
0
W
LP
WB
From
DF
NF
ES
LP
4
35705
42
29
73
6357
WB
0
14
3605
0
8
40
DF
0
8
0
642
0
0
NF
9
65
34
0
5371
141
ES
0
43
34
0
14
4964
Key: W = water, LP = lodgepole pine, WB = whitebark pine, DF = Douglas fir, NF = non-forested, ES =
Englemann Spruce. Total pixels = 57,212.
Table 2
Land Cover Types Changes as a Percent of the Total Number of Changed Pixels
W
-
W
LP
WB
From
DF
NF
ES
LP
0.0529
0.5558
0.3838
0.9660
84.1207
To
WB
0.1853
0.1059
0.5293
DF
0.1059
8.4954
-
NF
0.1191
0.8601
0.4499
1.8658
ES
0.5690
0.4499
0.1853
-
Table 3
Landscape Level Metrics
Area*
Core Area**
Diversity
Edge*
Form
Metric
Total Area (TA)
Number of Patches (NP)
Total Core Area (TCA)
Core Area Index (CAI)
Richness
Shannon's Diversity
Shannon's Evenness
Dominance
Total Edge (TE)
Mean Patch Edge (MPE)
Mean Shape Index (MSI)
Mean Perimeter-Area Ratio (MPAR)
Pre-Fire
110682918.32
103
105762970.9
95.55
6
1.073
0.599
0.719
499955.42
4853.94
1.666
0.026
Post-Fire
110682918.32
113
105604108.4
95.41
6
0.897
0.501
0.895
516804.87
4573.49
1.699
0.022
*All areas are in square meters and lengths are in meters. **Core area distance = 10 m
9
John Long
Table 4
Class Level Metrics
Area*
Core
Area**
Diversity
Edge
Form
Metric
NP
MPS
PSSD
NCA
CA
TCCA
CAI
Proportion
TE
MPE
MSI
MPAR
Water
Pre-fire
Post-fire
Lodgepole Pine
Pre-fire
Post-fire
2
1
8
11
16
15
21999.9
22436.9
8665885.97
7415979
450555.54
474005.55
2531.47
0
16063103.22
21425671.46
505280.85
504551.7
2
1
17
19
18
17
43999.9
22436.9
69327087.72
81575769.03
7208888.72
7110083.22
32844.8
16388.6
67609632.76
79477669.57
6658310.82
6571927.58
74.65
73.04
97.52
97.43
92.36
92.43
0.04
0.02
62.64
73.7
6.51
6.42
1194.21
652.23
172116.64
210666.74
55975.18
54745.2
597.11
652.23
21514.58
19151.52
3498.45
3649.68
1.136
1.228
2.209
2.031
1.637
1.641
0.027
0.029
0.021
0.021
0.018
0.012
Douglas Fir
Pre-fire
Post-fire
Area*
Core
Area**
Diversity
Edge
Form
NP
MPS
PSSD
NCA
CA
TCCA
CAI
Proportion
TE
MPE
MSI
MPAR
Whitebark Pine
Pre-fire
Post-fire
Non-forest
Pre-fire
Post-fire
Englemann Spruce
Pre-fire
Post-fire
10
10
40
31
27
45
128291.37
126084.48
265149.72
351078.55
822742.2
218452.2
98130.07
98647.16
629233.23
704690.53
3274177.3
513929.23
10
10
51
42
41
55
1282913.68
1260844.82
10605988.87
10883435.14
22214039
9830349.2
1134293.64
1113898.77
9376260.37
9687400.85
20951629
8736823.03
88.42
88.35
88.41
89.01
94.32
88.88
1.16
1.14
9.58
9.83
20.07
8.88
15278.32
15108.83
126589.57
122719.89
128801.5
112911.99
1527.83
1510.88
3164.74
3958.71
4770.43
2509.16
1.259
1.257
1.726
1.812
1.623
1.668
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
10
John Long
Figure 1.
Map of the Greater Yellowstone Ecosystem
11
John Long
Figure 2.
Map of the 1988 Yellowstone Fire Perimeters
12
John Long
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
13
John Long
Figure 5.
Map of Burn Types
14