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USING FIRE FOR BUTTERFLIES:
SOIL CHARACTERISTICS ACROSS A BURN GRADIENT
IN WESTERN WASHINGTON PRAIRIES
by
Robyn Andrusyszyn
A Thesis
Submitted in partial fulfillment
of the requirements for the degree
Master of Environmental Studies
The Evergreen State College
June 2013
©2013 by Robyn Andrusyszyn. All rights reserved.
This Thesis for the Master of Environmental Studies Degree
by
Robyn Andrusyszyn
has been approved for
The Evergreen State College
by
________________________
Carri LeRoy, Ph.D.
Member of the Faculty
________________________
Date
ABSTRACT
Using fire for butterflies: Soil characteristics across a burn gradient in western
Washington prairies
Robyn Andrusyszyn
Prescribed burning has become an important strategy for restoring Puget lowland
prairies in the Pacific Northwest. Mosaic burning is employed to create a large variety
of habitat conditions to help restore populations of rare species, including the
Taylor’s checkerspot butterfly (Euphydryas editha taylori). This important pollinator
species is very sensitive to microclimatic habitat conditions. To better understand the
microclimatic conditions provided by fire, as well as the succession of those
conditions, I evaluated surface temperature, subsurface temperature, and soil moisture
across a burn gradient from 2009 to 2013 at two different prairie sites on Joint-Base
Lewis-McChord. In the winter months of January through March 2013, temperatures
in areas last burned in 2009 were significantly cooler than temperatures from other
burn years. Soil moisture did not vary significantly among burn years. Regular
burning at an interval of every three to four years provides a warmer microclimate,
and supports the current estimated historic fire return interval. Maintaining these
habitat conditions may provide an advantage for Taylor’s checkerspot butterfly larval
success.
Table of Contents
List of Figures …………………………………………………………….…….…..v
Acknowledgements…………………………………………………………………vi
Chapter 1 – Literature Review.................................................................................1
Chapter 2 – Manuscript (formatted for Northwest Science)……………………….20
Introduction…………………………………………………………..…….20
Study Area………………………………………………………………….24
Methods…………………………………………………………………….26
Results……………………………………...…………………………….…29
Discussion…………………………………………………………………..34
Recommendations…………………………………………………………..36
Chapter 3 – Project Significance and Interdisciplinary Connections………………39
Extended Discussion..………………………………………………………39
Extended Future Research……………………………………….…….……43
Restoration Impacts…………………………………………………………46
Stakeholders…………………………………………………………………47
Interdisciplinary Practices….……………………………………….……….49
Fire Ecology and Sustainability: Case Studies……...………………………52
Conclusion…………………………………………………………….….….55
Bibliography….........................................................................................................56
Appendices…………………………………………………………………….….…62
Appendix A: Contrast Pairwise Comparison Results……………………….62
Appendix B: Sample Datalogger Data………………………………………64
Appendix C: Average Daily Air Temperature Influence…………………....66
iv
List of Figures
Figure 1: Burn mosaic patterns in Johnson prairie and Upper Weir prairie………..25
Figure 2: Plot locations………………………………………………………….…..25
Figure 3: Plot schematic……………………………………………………….….…27
Figure 4: Average surface temperature among burn year…………………………..30
Figure 5: Maximum surface temperature among burn year………………………...31
Figure 6: Light influence on temperature………………………...……...…….……31
Figure 7: Average subsurface temperature among burn year………………….……33
v
Acknowledgements
Many thanks to all of those who gave me support with my thesis project. I especially
thank Carri LeRoy for her support and guidance as my thesis reader. I would like to
thank the Center for Natural Lands Management, and in particular Sarah Hamman,
for sharing guidance, inspiration, and knowledge as to the design of this research
project. I also thank John Richardson and Joint-Base Lewis-McChord for allowing
me permission to conduct research on their property. Special thanks also to Dylan
Fischer for his advice and borrowed equipment. I would also like to thank Dennis
Aubrey, Adam Martin, and Cheryl Fimbel for sharing their knowledge and advice.
Thank you to Alison Baur for her field assistance and editing prowess. Finally, a very
special thank you to Nathan Pepin for his support, field assistance, and
encouragement.
vii
Chapter 1 - Literature Review
Fire Disturbances
Wildfires are a natural disturbance that regularly influences ecosystems. Fires
accelerate new growth, alter community structure, and diversify available habitat
(Noss et al. 2006). However, nuisance smoke, loss of natural resources, and the
potential danger to people have created a fear of wildfires since the late 19th century
(Dombeck et al. 2004). Recently we have begun to recognize the positive changes
that fire disturbance events have on the environment. Not only are there ecological
benefits from fires, but some ecosystems actually depend on fires for survival. In the
African bush, fires drive ecosystem dynamics and maintain the grassland-dominant
system (Parr and Andersen 2006, Ribeiro et al. 2008). Savannas in the southeastern
United States depend on fires to remove competing non-native species and allow the
coexistence of numerous native species (Kirkman et al. 2001, Parr and Andersen
2006). In the northwestern United States, prairies require fires to increase nutrient
availability to plants and open habitat for wildlife (Agee, 1996). The alteration of
natural fire regimes has modified forests and decreased prairie and oak woodland
habitat in the Pacific Northwest (Hamman et al. 2011). Fire disturbance events play a
crucial role in ecosystem maintenance and this has become even more apparent
through anthropogenic changes to natural fire regimes.
Native Americans demonstrated an early knowledge of fire benefits through
their use of fire to maintain certain ecosystems. As early as the 15th century, Native
Americans in the northwestern United States burned for agriculture as well as
hunting and gathering purposes (Shinn 1980, Walsh et al. 2010). A decline in Native
1
American populations, as well as the influence of Euro-Americans, led to a decrease
in fire activity in the early 20th century. In the 1930s the United States Forest Service
instituted fire suppression regulations intended to limit resource losses from wildfires
(Dombeck et al. 2004, Jensen and McPherson 2008). However, these fire suppression
practices are costly and largely have not been successful in preventing catastrophic
fires (Neary et al. 1999, Brown et al. 2004, Jensen and McPherson 2008). The
inability of fire suppression practices to prevent large-scale catastrophic wildfires has
led to a loss of natural resources. Some of the largest impacts are felt in logging
communities when large wildfires kill most, or sometimes all, of the trees that were
available for timber harvest (Noss et al. 2006). Furthermore, the negative ecological
impacts from fire suppression, including an increase in non-native species prevalence
and decreases in habitat heterogeneity, demonstrate that fire disturbances are crucial
components to ecosystem maintenance (Shinn 1980). Long-term fire suppression may
lead to an abundance of fuel for large, intensive fires. As fuel loads increase, potential
fire severity increases. When fire does come to such an area, it often burns hotter and
longer, causing increased resource and ecosystem damage. The natural mosaic that
would have previously prevented much of the area from being fully destroyed
diminishes as fuel loads increase (Noss et al. 2006). Instead of increasing the
potential for resource losses, proper maintenance of historic fire regimes can better
preserve resources.
In order to find a more effective method of preventing large-scale, destructive
fires, land managers have begun to reintroduce natural fire regimes to fire-dependent
ecosystems through prescribed burning. Prescribed burning for ecological
2
management became more common in the United States starting in the late 1980s
(Jensen and McPherson 2008), but this practice was used as early as the 1970s by
park managers in South Africa (Brown et al. 1991) and Australia (Bradstock et al.
1998). In 1995, the United States adopted the Federal Wildland Fire Management
Policy. This called for improved fire management plans and recognized that fire was
a fundamental ecological process (Jensen and McPherson 2008). The recognition of
fire as a necessary ecological process created a new challenge to land-managers to
effectively and safely incorporate burning into management plans (Stephens and Ruth
2005). Using prescribed fire, smaller and more controlled burns can maintain systems
while reducing the risk of future catastrophic wildfires. Land managers have been
experimenting with prescribed burning to appropriately and efficiently manage their
lands and to protect ecosystems from future catastrophic wildfires. In addition to
protection from future wildfires, prescribed burns can be used to achieve other
management goals such as nutrient supplementation, habitat enhancement, and
reduction in non-native plant species cover.
Using prescribed fire, restoration managers are attempting to further
understand fire effects and how to optimize the benefits fire disturbances can provide
(Dunwiddie and Bakker 2011). This destructive disturbance provides unique
influences on ecosystem functions that are difficult to imitate through other
techniques (Harrington and Kathol 2009). Finding a balance between obtaining fire
benefits and protecting people and their property is a new challenge for ecological
restoration and management. The spread of human development into fire-dependent
3
ecosystems emphasizes the need to live effectively, and safely, with regular fire
disturbances (Dombeck et al. 2004).
Prairie Degradation and Fire in Restoration
Prairies are flat, grass-covered ecosystems that are historically adapted to regular fire
influences. Prairies are found in areas such as the Midwest and northwestern United
States. Retreating glaciers created the Puget lowland prairies of western Washington,
which are now very rare and fragmented ecosystems. An estimated 95-99% of native
prairies in the Pacific Northwest have been lost to urban development and coniferous
forest encroachment since the early 20th century, leaving less than 17,000 ha of
fragmented habitat remaining (Hamman et al. 2011). These unique ecosystems not
only benefit from fire disturbance events, but depend on them to maintain ecological
functions. Native American burning historically maintained the Puget lowland
prairies, using fire to improve landscapes for agriculture. This encouraged crops such
common camas (Camassia quamash), and maintained pastures for grazing herd
animals. These practices depended on regular fires to manipulate herd movements
and increase nutrient availability in the otherwise nutrient-poor soils of the prairies
(Boyd 2002). Frequent low-intensity fires were used to obtain the beneficial
influences of fire without a large amount of destruction, maintaining a fire return
interval of approximately two to three years (Agee 1996, Rook et al. 2011). The
reduced frequency and extent of anthropogenic burning following declines in Native
American populations, the influx of Euro-Americans, and the onset of fire
suppression practices has increased the loss and degradation of this ecosystem (Walsh
4
et al. 2010, Rook et al. 2011). Without regular burning, noxious invasive species have
become widespread and there continues to be encroachment of coniferous forests
(Walsh et al. 2010, Hamman et al. 2011).
The sharp decline in prairies has led to a recent increase in restoration efforts.
An important component of those efforts is the re-introduction of regular fire
disturbance events through prescribed burning. Regular short-interval burning of
prairies stimulates plant growth, creates open habitat, and decreases the risk of
catastrophic wildfires by reducing fuel accumulation (Agee 1996). Additionally,
native plant species that are historically well-adapted to frequent fires may persist
over non-native plant species under a frequent fire regime (Hamman et al 2011).
Through this effort, the hope is to restore habitat to support populations of
endangered and threatened animal species such as the Taylor’s checkerspot butterfly
(Euphydryas editha taylori) and the streaked horned lark (Eremophila alpestris
strigata), while preventing further decline of other increasingly rare fire-dependent
and prairie-dependent species. Prescribed burning is a cost-effective and timeeffective practice that provides habitat enhancement through thatch removal, invasive
species removal, and snag creation (Harrington and Kathol, 2009). Regular fires at
appropriate fire return intervals can reduce available fuel, maintain open space for
new growth, and alter nutrient availability (Neary et al. 1999). Research continues to
evaluate the effects of prescribed fires on soils, vegetation, and wildlife, creating
evidence to support prescribed burning as a valuable tool in restoration from the
perspective of both the public and land managers.
5
Prescribed burning can achieve many restoration goals at a cheaper and more
effective rate than other techniques. Restoration goals include creating habitat for rare
fauna and reducing the cover of non-native noxious plant species. Prescribed burning
addresses both of these goals in that it can immediately top-kill non-native species
including the noxious Scotchbroom (Cytisus scoparius) (USDA NRCS 2013), while
providing nutrients and space for native species to return (Rook et al. 2011, Stanley et
al. 2011). Fire surrogates such as herbicide and mowing are also used to remove nonnative species, however at the cost of increased time, effort, and money. Burning can
remove acres of Scotchbroom within a few hours, while the same area could take
days with herbicide treatment or mowing. Additionally, burning facilitates the
removal of thatch and moss as well as the conversion of nutrients in the soil
(Harrington and Kathol 2009, Hamman et al. 2011). These influences provide more
opportunity for fire-adapted native plant species to out-compete non-native species.
Typically fire surrogate techniques are limited in their ability to provide equivalent
conservation benefits and are at a higher cost per unit area of land treated compared
with prescribed burning (Harrington and Kathol 2009). Maintaining regular
prescribed burning events contributes the unique benefits that only fire can provide.
As prescribed fire becomes an increasingly influential restoration tool,
knowledge gaps in optimal fire frequency and fire season, species-specific responses,
and alternatives to burning become more apparent (Rook et al. 2011). Despite
increased management experience in these prairies, there is a lack of quantitative data
to support anecdotal evidence of fire effects on soil characteristics, vegetation growth,
and wildlife survival (Dunwiddie and Bakker 2011, Granged et al. 2011).
6
Understanding the long-term impacts of fire on post-burn physical, chemical, and
microbial characteristics provides a basis for management decisions. Using this
knowledge to better predict future fire behavior and influences will improve the
effectiveness of prescribed fires as a management tool. This information may also
enhance the predictability of future prescribed burns and wildfires. In turn, the
improved management of Puget lowland prairies may reduce the risk of personal
injury and property loss to fires while maintaining vibrant and robust prairie
ecosystems into the future.
Fire Effects
Fire disturbances have profound effects on the ecosystems they invade. These effects
drastically change the landscape, starting with the soil. At first glance, burned areas
epitomize destruction and eradication. However, burning transforms nutrients, opens
up habitat, and increases the competitive advantage for native species to thrive over
non-native species (Shinn 1980, Noss et al. 2006, Hamman et al 2011). Soil
characteristics provide the basic building blocks for ecosystem structure and function.
Physical and chemical properties of soil, such as temperature, moisture-holding
capacity, and nutrient content, influence the recovery of ecosystems following burn
events. Characteristic changes in soil microclimate following fire include: changes in
surface albedo, reductions in plant density, and increases in nutrient availability.
Topographical variation, patchy vegetation, and a variety of moisture levels create
diversified soil microclimates across burned prairie landscapes (Gibson et al. 1990,
Hart et al. 2005). These habitat variations, along with increased diversity from mosaic
7
burn patterns, improve habitat and promote species diversity. Understanding specific
fire influences in each ecosystem may promote better management and restoration of
fire-dependent ecosystems.
Soil Temperature
Changes in soil temperature impact the survivability of wildlife, the development of
microbial communities, and the growth of plant species. Following a burn event,
plant and thatch density is reduced and the soil becomes blackened (Neary et al.
1999). These changes to the soil may create increased daytime temperatures and more
rapid loss of heat at night (Kasischke et al. 2007). Seasonal differences include earlier
freezing in winter and earlier warming in spring (Fisher and Binkley 2000, Hart et al.
2005). Snyman (2003) investigated differences in unburned and burned patches
following a bush fire in South Africa, and concluded that burned areas showed a
significant increase in soil temperature in the year post-fire. This was assumed to be
partly because of a strong decrease in plant basal cover. In Alaskan black spruce
forests, Kasischke et al. (2007) concluded that for the first several decades following
a fire, soil temperatures remained elevated. Understanding the relationship between
burn events and soil temperature may increase the predictability of plant community
recovery and may directly influence prairie-dependent species.
Wildlife can be extremely sensitive to temperature conditions. Post-fire, warmer
soil temperatures can increase the growth of food plants and alter winter survivability
of animals. Temporary increases in bird and mouse observations occur in recently
burned areas, possibly due to increases in food supplies and soil temperature changes
8
(Bock and Bock 1983). After a fire in the Sierra Nevada foothills, nesting bird density
and large predator density increased (Lawrence, 1966). Species diversity can also
change in relation to new habitat characteristics that are created from fire
disturbances; fire-adapted species that thrive on a warmer, more open habitat increase
in abundance after a burn, while species requiring more sheltered conditions tend to
leave a burned area (Simons 1991, Tiedemann et al. 2000). Fire can also directly have
a negative impact on species when animals are unable to escape an oncoming fire,
most commonly rodents, small amphibians, and insects.
Soil microbial communities drive nutrient conversion and form mutualistic
relationships with plants (Hart et al. 2005). Fire influences on microbial communities
create concomitant reactions throughout plant communities. Microbial mortality can
occur from increased soil temperatures during a fire event, which in turn influences
the recovering plant community (Neary et al. 1999, Hart et al. 2005). Nutrient
demands and mutualistic relationships vary based on both microbe- and plantavailability post-burn (Neary et al. 1999). Microbial and plant communities
simultaneously depend on one another for post-burn recovery.
Surface temperatures reached both during a fire and in the months following a fire
strongly influence the plant community that recovers. Increases in temperatures,
especially daytime temperatures, can accelerate plant growth and productivity
(Heuvelink 1989). Soil temperature can also influence the germination of plants postfire. Native plant species that are better adapted to exposure to high temperatures are
likely to be given competitive advantage over non-native plant species that become
established when fire is excluded from the ecosystem. One strategy employed by fire-
9
adapted plants is the creation of a seed bank in the soil. These dormant seeds are
protected by strong seed coats that need the intense heat of a burn to break dormancy
and germinate (Keeley 1987, Agee 1996). Different seeds have different temperature
requirements to break dormancy, but some fires create soil temperatures that are
warm enough to destroy seeds. Furthermore, topographical variation creates
temperature variation both during and after a fire. Variation in burn season also
typically has a strong influence on which seeds break dormancy. For example,
Bradstock and Auld (1995) demonstrated that the increase in soil temperature after a
summer fire could be enough to break seed dormancy for some plant species, but the
same was not true following a winter fire. The plant community that recovers postburn will depend on which seeds are able to break dormancy and the growing
conditions available on a micro-scale.
Nutrient Levels
In addition to changes in temperature, soil nutrient availability changes after the
passage of a fire. The intense heat modifies soil stability, alters chemical
compositions, and adds new soil nutrients from burned plant matter (Neary et al.
1999). There is a tendency to lose nutrients overall during a fire, but the amount of
plant-available nutrients increases (Kutiel and Naveh 1987, Vose et al. 1999).
However, the variation in fire intensity, as well as spatial heterogeneity across
landscapes, can produce different results in nutrient fluxes; chemical reactions in the
soil are altered by variation in heat and fire residence time (Kasischke et al. 2007,
Savadogo et al. 2012). Marion et al. (1991) investigated the effects of fire and ash on
10
soil nutrients, and found an increase in availability of all investigated nutrients (NH4N, NO3-N, PO4-P, Ca, Mg and K) in surface soil post-fire. However as fire severity
increases, some of those nutrients decreased, while others increased. In addition,
nutrients found in dead thatch are quickly returned to the soil for the use of growing
plants following a fire. Nutrient levels in the soil provide building blocks for plant
growth. During a burn some carbon is transformed into charcoal for long-term storage
(DeLuca and Aplet 2008). While some fires cause a decrease in soil organic matter,
increases in surface soil organic matter also occur, especially in forested areas where
an input of leaves and other plant materials can influence fire behavior and soil
composition (Mataix-Solera et al. 2011). Scharenbroch et al. (2012) discovered
burned areas had increased total nitrogen and total organic carbon levels compared
with unburned counterparts. The new growth of the post-burn recovering plant
community is accelerated through the help of this influx of available nutrients, and
can demonstrate patchy fire effects (Hart et al. 2005).
Changes in nutrient properties also contribute to post-fire changes in soil
structure and aggregate stability. Erosion becomes a concern due to decreased plant
cover and altered soil texture and stability post-fire. This may mean that immediately
post-fire more nutrients are available, but those nutrients may leach away as that soil
erodes (Neary et al. 1999, Granged et al. 2011). Combined, these factors are
important in understanding fire effects on erosion and future plant communities
(Granged et al. 2011, Mataix-Solera et al. 2011).
11
Soil Moisture
Fires also influence soil moisture levels. The ability of a soil to hold or lose moisture
changes after a burn due to changes in soil texture and water-repellency layers.
Belowground hydrologic properties support vegetation growth, and in-turn affect
ecosystem functioning (Neary et al. 1999). A lack of post-burn moisture availability
may limit all vegetation growth, and provide a poor microclimate (Augustine and
Milchunas 2009). Restoration of fire-dependent ecosystems is often contingent on
native plant species being better adapted to adverse moisture levels than undesirable
non-native plant species. Knowing post-fire moisture levels can indicate the success
rate of rare plant species thriving and out-competing non-native species that are not as
well-adapted to adverse moisture conditions (Hamman et al. 2011). Soil moisture is a
valuable characteristic that can be used to predict plant species distribution and
productivity as well as future fire intensity (Bekker and Taylor 2001, Lenihan et al,
2003, Augustine and Milchunas 2009). In other ecosystems, fire greatly influences
soil moisture. Granged et al. (2011) found that following a fire in the Mediterranean
the proportion of water-repellent soil decreased, and remained lower than pre-fire
conditions for three years. Through the use of satellite imagery, Kasischke et al.
(2007) concluded that fire in black spruce forests led to a decrease in soil moisture for
several decades following a fire. Snyman (2003) also detected significant decreases in
soil moisture for two years following a burn in South Africa. In the climate of western
Washington, with very wet winters and dry summers, the importance of changing
water repellency layers and moisture levels may be even more important. Summer
12
droughts can create extreme microclimate conditions, and water-deprived plants have
diminished chances for survival during a drought.
Fire Influences on Butterfly Habitat
Conservation of increasingly rare and endangered prairie-dependent species is a top
priority in restoration efforts. The focus of many of these efforts concentrates on the
recovery of multiple butterfly species, including the Taylor’s checkerspot butterfly
and Mardon skipper (Polites mardon). Prairie-dependent species have become rare
due to the decline in their habitat. Among others, the Taylor’s checkerspot butterfly is
currently a candidate species to be listed as endangered under the Federal Endangered
Species Act. Much emphasis has been placed on these rare butterflies because of their
important role as pollinators. Pollinator capacity represents an important ecological
function that can sustain plant reproductive resilience (Dixon 2009). Because of their
high sensitivity, butterflies are often used as indicators of habitat quality on both a
macro- and micro-habitat scale (Vanreusel and Van Dyck 2007, Beyer and Schultz
2010). Specifically for western Washington butterflies, recovery may also be strongly
tied to the recovery of several rare plant species (Adler 2003, Caplow 2004).
The effects of fire on soil characteristics also indirectly influence dependent
animal species through plant community responses to different soil conditions. The
productivity of plants is a function of available moisture, temperature, and nutrient
composition, all of which are altered by burning (Lenihan et al. 2003). An important
characteristic of ideal butterfly habitat is not only the presence of host and food
plants, but also the timing of the different stages of these plants. Changes in
13
phenotypic plasticity in response to recent burning creates changes in flowering time,
the number and size of blooms, and extended active growth phases in a variety of
species in Southeastern Oregon, including modoc hawksbeard (Crepis modocensi),
Nevada biscuitroot (Lomatiun nevadense), and slender phlox (Phlox gracilis)
(Wrobleski and Kauffman 2003, USDA NRCS 2013). Anecdotally, similar
phenological changes have been seen in Puget lowland prairies (Sarah Hamman,
personal communication April 2012). Specifically for butterflies, differences in
germination rates and the timing of senescence can limit the availability of food and
host plants during the various life cycle stages (Weiss et al. 1988). Interestingly, an
increase in butterfly oviposition rates has been found in prairies throughout
Washington, Oregon, and British Columbia in conjunction with increases in native
nectar resources post-fire (Schultz et al. 2011).
Butterfly survival throughout various life cycle stages requires specific
temperature and moisture levels (Weiss et al. 1988, Beyer and Schultz 2010). Warm
soil surfaces are used for basking, which allows butterflies to thermoregulate.
Thermoregulation also allows for survival at larval stages and increases oviposition
success in adult stages (Severns 2007). Temperature also impacts the timing of
various life cycle stages, giving butterflies external cues for larval diapause, pupation,
and adulthood. The highly seasonal climate of the Pacific Northwest places time
constraints on butterfly development (Weiss et al. 1988). Spatial variation in soil
temperature has been shown to be strongly related to reproductive success of adults,
timing of flying females, and the mass and survivability of larvae (Weiss et al. 1988,
Severns 2007). Areas of high local topographical variability provide more
14
opportunities for long-term population survival. The reintroduction of regular fire
events increases the diversity of available microclimates. Microclimatic and
topographical variations are particularly influential for bay checkerspot butterfly
(Euphydryas editha bayensis) populations in northern California, a subspecies similar
to the Taylor’s checkerspot butterfly of the Puget lowlands (Weiss et al. 1988).
Spatial variation in plant communities can also provide more basking sites and native
plant availability (Severns 2007).
Future Challenges to Prairie Restoration
There are numerous ecological and social questions to be answered concerning the
use of fire for successful prairie restoration. Prescribed fire has been used in other
systems, but there is a lack of quantitative information on fire effects specific to Puget
lowland prairies (Dunwiddie and Bakker 2011). Hamman et al. (2011) demonstrated
some of the first attempts to quantify short-term post-fire effects, such as fire severity
and bare ground creation, finding significant differences in vegetation, moss, and
thatch cover immediately after a burn. However, the long-term impacts on these
habitat characteristics are typically not quantified. A better understanding of lasting
effects can determine optimal fire return intervals for this threatened ecosystem.
Furthermore, improving the predictability of lasting fire influences will assist land
managers in creating butterfly habitat management plans.
Public perception and acceptance of prairie restoration, especially concerning
prescribed burning, is essential for management success. The extreme rarity of this
ecosystem can pose challenges in justifying the effort to restore it. Additionally,
15
prescribed burning affects the public in many unavoidable ways. Nuisance smoke can
be difficult to control and may pose health risks to nearby communities. While much
effort is made concerning safety for both people and property during anthropogenic
burn events, there are still risks to human lives and the potential for damage to nearby
property. The public’s perception and knowledge concerning the safety precautions
taken by firefighters is imperative for burn operations to occur as numerous public
complaints can prevent a burn from happening before it starts. Furthermore, the
ecological need for fire disturbances is not often intuitive, and the sights, sounds, and
smells of wildfires are often alarming. Another common concern of the public is the
management of nearby lands. If endangered wildlife exists on private property it may
not only impact the way that landowner manages his property but may also pose
additional costs to the landowner; requirements to preserve habitat for an endangered
species can even motivate a landowner to prevent endangered species from being
found on their property by government scientists (Shogren et al. 1999). Enhancing
and increasing available habitat can alter the spread of species of concern and
hopefully prevent or improve the endangered status of species to eliminate the
concern for both restoration managers and private landowners. Only through public
cooperation can measures such as these be taken. Informing the public about the
ecological benefits of fire to Puget lowland prairies and the efforts to restore them
may prove to be critical to maximizing both the ecological benefits for prairies and
the health and safety of people.
Reducing the likelihood of catastrophic wildfires through the use of prescribed
burning is increasingly important as human populations spread to areas with a higher
16
likelihood of wildfires. As the wildland-urban interface continues to shift,
management practices in those areas need to adjust to protect people as well as the
environment. Increasing development can increase habitat fragmentation and the
spread of non-native species (Radeloff et al. 2005). The responsibility for protecting
houses, lives, and property is also divided between private landowners and governing
systems. This creates a challenge in defining how that responsibility is appropriately
shared. As the number of people living within the wildland-urban interface increases,
there is increased difficulty in evacuating those people safely. In these areas
evacuation needs to happen more quickly due to the close proximity to fuels and the
decreased defensibility of property (Cova 2005). In addition to more human lives at
risk in these areas, increases in accidental anthropogenic wildfires are also likely to
occur (Jensen and McPherson 2008). For protection of the ecological value of the
wildland-urban interface and the people who have made these areas home, accidental
wildfire protection and education is fundamental. An increasing human population
creates an increased need for cooperation between restoration efforts and the public as
the wildland-urban interface expands in fire-prone areas.
Another future challenge to restoration and conservation efforts, not only in
prairies but in all ecosystems, is the potential complex influences of climate change.
The frequency and intensity of wildfires is very likely to be affected by a changing
climate, especially in synergy with increased urban development and habitat
fragmentation (Lawson et al. 2012). Longer, warmer, and drier summers will extend
the duration of the fire season and increase the risk of catastrophic wildfires (Brown
et al. 2004, Flannigan et al. 2009). Furthermore, changes in temperature and moisture
17
will alter the vegetation composition and productivity of ecosystems, leading to more
changes in habitats and fire behavior (Lenihan et al. 2003). The forested areas of the
Northwest, many of which border prairie habitat, are of particular concern for climate
change impacts. Forests tend to accumulate large amounts of fuel which poses a much
higher fire danger, particularly under dry climate conditions (Brown et al. 2004).
Puget lowland prairies, however, may not be as disadvantaged in a warmer and drier
climate as other systems; native flora may thrive in areas no longer suitable for forests
in more extreme climate conditions (Bachelet et al. 2011). More difficult to predict,
however, are the reactions of non-native species to climate change, many of which
have already demonstrated their high-adaptability by establishing themselves in many
systems (Bachelet et al. 2011). Plant community changes as a result of climate change
will concomitantly influence fire regimes (Lenihan et al. 2003).
Predicting wildland fire behavior is a complex endeavor, made increasingly
difficult by potential changes in climate (Hély et al. 2000). On a daily basis, even
slight weather changes can dramatically alter fire behavior (Bessie and Johnson
1995). In a drier, warmer, and longer fire season, the ability of wildland firefighters to
predict, alter, or suppress wildfires may be compromised (Hély et al. 2000).
Furthermore, an altered climate that increases fire-prone areas also increases the
wildland-urban interface (Dombeck et al. 2004). People that were previously not
living in a high fire-risk area may unknowingly now live with increased risk.
Improving our understanding of both short- and long-term fire effects can strengthen
predictions concerning climate change effects as well as help managers to adapt
restoration plans for the protection of both prairies and people.
18
Ecosystem management is influenced by fire disturbances across a landscape.
In order to better understand how prescribed burning in Puget lowland prairies
influences plant and butterfly habitat, I investigated changes in soil temperature and
moisture across a burn gradient. Based on patterns found in other ecosystems, I
wanted to understand if Puget lowland prairies also have increased soil temperature
and decreased soil moisture after burning, and how long those changes persist. The
primary purpose of this experiment was to determine how changes in these soil
characteristics impact sensitive butterfly species; however, many plant and animal
species may also be affected by these soil changes.
19
Chapter 2 – Manuscript (formatted for Northwest Science)
Introduction
Wildfires are disturbances that influence a variety of ecosystems across the United
States. Fires provide unique and beneficial influences to those ecosystems. However,
increases in human population and development within fire-prone areas led to an era
of fire suppression beginning in the early 1900s (Dombeck et al. 2004). The goal of
fire suppression policy was to stop all catastrophic and destructive wildfires;
however, this policy was largely unsuccessful at reducing the total area of land
burned every year (Stephens and Ruth 2005, Jensen and McPherson 2008).
Furthermore, with the exclusion of regular fire influences from historically firedependent systems, the vital role of fire disturbances in ecosystem maintenance and
function became increasingly clear (Parr and Andersen 2006). When fires pass
through an ecosystem, they alter plant community structure, reinvigorate growth, and
diversify habitat (Noss et al. 2006). Fire disturbances also contribute to ecosystem
maintenance by reducing thatch cover and overcrowding (Knapp and Keeley 2006).
The current policy challenge is to protect both human populations and fire-dependent
ecosystems in an effective and cost-efficient manner (Harrington and Kathol 2009).
Rather than attempting to suppress every fire, learning to live cooperatively with fire
improves environmental, economic, and social components of sustainability
(Dombeck et al. 2004).
Puget lowland prairies are fire-dependent, grassland ecosystems in the
northwestern United States. The reduction of fire disturbances in this ecosystem has
diminished prairie quality and quantity. Current estimates demonstrate that only 1-5%
20
of native prairies remain compared to the early 20th century (Lawrence and Kaye
2011, Hamman et al. 2011). The remaining prairie habitat is highly fragmented and
degraded. Native Americans once maintained these glacial outwash prairies through
anthropogenic fires for agricultural, hunting, and social purposes (Shinn 1980, Walsh
et al. 2010); however, without regular fire influences, non-native vegetation and
coniferous forests have invaded these sensitive systems (Dunwiddie and Bakker
2011, Hamman et al. 2011). Plant community and soil nutrient alterations have led to
a concomitant reduction in wildlife populations. Observed changes in community
structure, species decline, and native plant cover have created a need for increased
management of prairies before they disappear. Recent anthropogenic managers of
prairies are now attempting to restore ecological structures and native plant cover to
this historically fire-dependent ecosystem.
For restoration success, prairie managers are attempting to reestablish
populations of declining, threatened, and endangered prairie species. Of particular
focus is the restoration of species that provide key ecological services. Butterflies
fulfill a crucial ecosystem function by providing pollination services, increasing the
reproductive and genetic resilience of plant communities (Dixon 2009). Priority
prairie species include the Taylor’s checkerspot butterfly (Euphydryas editha taylori),
which is currently a candidate for endangered species listing under the Federal
Endangered Species Act (ESA). These highly sensitive butterfly species serve as
indicators of macro- and micro-habitat quality (Vanreusel and Van Dyck 2007, Beyer
and Schultz 2010). Furthermore, the successful restoration of pollinating butterfly
species is also predicted to be directly tied to the restoration of several endangered
21
plant species including golden paintbrush (Castilleja levisecta; ESA status:
threatened, WA state status: endangered) (Adler 2003, Caplow 2004, USDA NRCS
2013). Successful butterfly populations help to maintain healthy plant communities
and increase the overall sustainability of prairie ecosystems. Established and
reproducing butterfly populations can also provide crucial feedback about the ability
of current restoration strategies, including prescribed fire, to create high quality
habitat.
The recent re-introduction of fire to Puget lowland prairies through prescribed
burning demonstrates enormous potential as a key strategy for restoring and
preserving the few remaining prairies in the Pacific Northwest (Hamman et al. 2011).
Fire influences several important habitat factors for sensitive species. For the Taylor’s
checkerspot butterfly, important influences of fire include altered phenology of food
and host plants and microclimatic variation in temperature and moisture (Weiss et al.
1988). One of the primary uses of prescribed burning is for removal of noxious nonnative species, such as Scotchbroom (Cytisus scoparius, USDA NRCS 2013), which
can alter the habitat structure of these short-grass prairies. Without fire influences,
increased thatch and tall non-native plants negatively impact butterfly behaviors
including basking, puddling, and oviposition (Lawrence and Kaye 2011). Through
experiments using a chronosequence of burns, we hope to find an optimum fire return
interval, or fire frequency, for prairie sustainability. Currently estimated at every 2-5
years, an appropriate fire return interval may maximize biodiversity and habitat
availability while still providing ample time for post-burn recovery (Agee 1996, Rook
et al. 2011). The long-term benefits from fire can be maximized through mosaic burn
22
patterns and maintaining an appropriate fire return interval. Establishing more
frequent, but smaller and less intense fires can actually decrease the likelihood of
catastrophic wildfires that damage property and risk human lives (Brown et al. 2004).
This may also increase ecosystem resilience while simultaneously creating
microhabitat heterogeneity that is ideal for butterflies.
The most dramatic fire influences on a landscape often involve soil. Soil
characteristics are the building blocks of an ecosystem and drive the available habitat
for plants and rare species such as the Taylor’s checkerspot butterfly. Both physical
and chemical changes to the soil after a burn influence plant community recovery.
Variation in soil temperature and moisture influence the germination and growth of
seeds in the post-burn community (Wrobleski and Kauffman 2003). The altered plant
community determines which wildlife populations succeed. For butterfly restoration,
the availability of host and food plants, as well as the phenological timing of those
plants, determines the reproductive success of each population (Weiss et al. 1988).
Chemical changes and soil blackening create temperature variation (Neary et al.
1999). Butterflies depend on warm soil surfaces for basking and thermoregulation at
multiple life stages (Weiss et al. 1988, Stinson 2005, Beyer and Schultz 2010).
Thermoregulation improves larval growth and survival as well as adult butterfly
oviposition success (Severns 2007). A common strategy for Taylor’s checkerspot
butterfly restoration is to release captive-bred larvae following a burn, assuming that
this provides larvae with advantages such as increased temperatures. Establishing the
long-term temperature pattern as a community recovers from a burn may indicate
when and where ideal butterfly habitat conditions exist.
23
The importance of butterflies to restoration success and the increasingly
widespread practice of prescribed burning led us to investigate the soil characteristics
created by mosaic burning that may influence butterfly distribution and reproductive
success. In order to investigate the physical characteristics of the ground surface
during the approximate larval stage of Taylor’s checkerspot butterflies, we addressed
several research hypotheses: 1) prairie surface temperature would be warmer and
more variable following recent burns. 2) subsurface soil temperature at a depth of 5
cm would be warmer and more variable following recent burns. 3) soil moisture
would be lower following recent burns.
Study Area
This study took place on two of the remaining Puget lowland prairies: Johnson prairie
and Upper Weir prairie. These prairies are located on Joint Base Lewis-McChord
near Rainier, Washington, and are approximately 1 km apart. Both areas have similar
topographical variation and are military training sites. These short-grass prairies are
presently managed through the use of prescribed burning and native seeding for
restoration and habitat enhancement. Burning occurs in a mosaic pattern (Figure 1) to
maximize the diversity of micro-habitats. On each prairie we established eight 40 m2
plots (Figure 2), two plots per burn year (2009, 2010, 2011, and 2012) at close
proximity to minimize travel time among plots. At Upper Weir prairie we established
two additional plots for 2013 when a section of prairie was burned in February 2013.
24
Prairie Burn Mosaic
Johnson Prairie
Upper Weir Prairie
Figure 1: Burn mosaic patterns of Johnson prairie and Upper Weir prairie. Areas
coded by burn year: 2009 (
Johnson Prairie
), 2010 (
), 2011 (
), 2012 (
), 2013 (
).
Upper Weir Prairie
Figure 2: Modified-Whittaker plot locations at Johnson prairie and Upper Weir
prairie. Plot color coded by burn year: 2009 (green), 2010 (orange), 2011 (red), 2012
(blue), and 2013 (purple).
25
Methods
Soil Temperature
Several methods were used to record soil temperature. An infrared thermometer (CenTech Model #96451) was used to measure surface temperature. Six measurements
were taken following a grid pattern in each plot (Figure 3), with a maximum distance
between points of 10 m to account for the suspected maximum daily travel distance of
butterfly larvae (Weiss et al. 1988). Simultaneously, two soil thermometers spaced
15 m apart were used to record subsurface temperature at a depth of 5 cm (Figure 3).
Each measurement was recorded weekly (with the occasional exception of Upper
Weir when military training prohibited access to the site) and within the hours of
1100 and 1400. One HOBO datalogger (Model # UA-002-08) per burn year was
located centrally between each burn year plot to record continuous surface
temperature and relative light intensity every 10 minutes (Figure 3). Due to the
limited availability of dataloggers, there were several weeks when we did not have a
datalogger for every burn year at each site. In this case, the datalogger most central to
all the plots was referenced.
26
Figure 3: Plot layout per year, including measurement locations for surface
temperature, subsurface soil (5 cm depth) temperature, soil moisture, and dataloggers.
Soil Moisture
Soil cores, with a diameter of 1.5 cm and 5 cm deep, were taken from Johnson prairie
in early February 2013 and from both sites in early March 2013. Soil moisture
content was calculated using gravimetric water content protocols (Black 1965).
Within each plot two cores were taken, 15 m apart. A 15 mL subsample from each
soil core was weighed in its “wet” state, and then dried in a 105°C oven for 48 hours.
Each sample was re-weighed in its “dry” state to determine percent moisture. The
moisture content within each plot was then averaged for analysis.
27
Statistical Analysis
Weekly soil surface temperatures were standardized to the corresponding
HOBO datalogger light and temperature data as if they were all recorded at 1200.
Subsurface soil temperature at 5 cm was assumed to be negligibly affected by the
change in sunlight and surface temperature over the course of the two hours during
which the measurements were recorded due to increased insulation from moss and
thatch layers. Results from the 2013 plots located in Upper Weir were not included in
statistical analyses because they were not replicated at the time of this study.
Repeated measures ANOVA was used to evaluate relationships found
between surface temperature and plots over time. The average surface temperature,
maximum surface temperature, and surface temperature standard deviation for each
plot at each site for eight weeks were analyzed. Similarly, a repeated measures
ANOVA was used to investigate the influence of the fire chronosequence on average
subsurface temperature and subsurface temperature standard deviations. Post-hoc
orthogonal contrast comparisons were used to further investigate patterns. The
influence of average daily air temperature (as recorded by the Ft. Lewis weather
station via <http://www.wunderground.com>) on surface and subsurface
temperatures, was evaluated through a regression analysis. Furthermore, we evaluated
the influence of light intensity on surface temperature through a regression analysis of
measurements from the dataloggers.
We used a regression analysis to compare average soil moisture variation with
burn year in March (February measurements were omitted from regression analysis
28
due to limited replication). A student’s t-test was used to compare differences
between February and March measurements.
Results
Surface Temperature
When comparing average surface temperatures across the burn chronosequence using
a repeated measures ANOVA, burn year had a significant influence on average
surface temperature (F(3,4)=30.4225, p=0.0033; Figure 4). Orthogonal contrast
comparisons demonstrated that 2009 temperatures were significantly colder than all
other burn years (Figure 4, Appendix A). Surface temperatures for 2010, 2011, and
2012 were all relatively similar. Midday surface temperatures from infrared
thermometer measurements were supported by continuous datalogger measurements
(Appendix B). Average daily air temperature had a positive correlation with surface
temperature, accounting for approximately 19% of the variation in surface
temperature (R2=0.1875, p<0.0001, Appendix C). Average surface temperature was
more strongly positively influenced by light intensity (R2=0.4649, p<0.0001; Figure
6). Light intensity accounted for approximately 46% of the variation in surface
temperature.
There were also significant differences in maximum surface temperature
among burn years (F(3,4)=11.3678, p=0.0199; Figure 5). Similar to average surface
temperatures, orthogonal contrast comparisons of maximum surface temperatures
demonstrated that 2009 temperatures were significantly cooler compared to all other
burn years and maximum surface temperatures for 2010, 2011, and 2012 were all
29
relatively similar (Figure 5, Appendix A). Average air temperature also had a positive
correlation with maximum surface temperature, but only accounted for approximately
13% of the variation in maximum surface temperature (R2=0.1292, p<0.001,
Appendix C).
Standard deviation of surface temperature within each plot ranged between
0.2°C and 3.4°C. Burn year did not significantly influence the variation of surface
temperature within each plot (F(3,4)=0.6656, p=0.6156). Standard deviations also did
not show a strong response to average daily air temperature (R2=0.0123, p=0.1451,
Appendix C).
LSM Average Plot Surface Temperature
30
2009 A
25
F(3,4)=30.4225, p=0.0033
2010 B
2011 B
2012 B
Temperature (°C)
20
air temp
15
10
5
0
15-Jan
25-Jan
4-Feb
14-Feb
24-Feb
5-Mar
15-Mar
25-Mar
4-Apr
Figure 4: Results from a repeated measures ANOVA for average plot surface
temperature compared with burn year, represented by least squares means
(F(3,4)=30.4225, p=0.0033). Years are coded as follows: 2009 (green), 2010 (orange),
2011 (red), and 2012 (blue). Average air temperature is shown as a dotted black line.
30
LSM Maximum Plot Surface Temperature
35
2009 A
30
F(3,4)=11.3678, p=0.0199
2010 B
2011 B
2012 B
25
Temperature (°C)
air temp
20
15
10
5
0
15-Jan
25-Jan
4-Feb
14-Feb
24-Feb
5-Mar
15-Mar
25-Mar
4-Apr
Figure 5: Results from a repeated measures ANOVA for maximum plot surface
temperature compared with burn year, represented by least squares means
(F(3,4)=11.3678, p=0.0199). Years are coded as follows: 2009 (green), 2010 (orange),
2011 (red), and 2012 (blue). Average air temperature is shown as a dotted black line.
Temperature vs. Light
50
R2 = 0.4649, p<0.0001
40
Temperature (°C)
30
20
10
0
0
50000
100000
150000
200000
250000
300000
-10
-20
Light Intensity (lux)
Figure 6: Influence of light intensity (lux) on prairie surface temperature (°C), as
measured by HOBO data loggers from January through March 2013.
31
Subsurface Soil Temperature
Comparing the influence of a burn chronosequence on subsurface temperatures
throughout time using a repeated measures ANOVA demonstrated that burn year had
a significant influence on average subsurface temperature (F(3,4)= 8.891, p=0.019,
Figure 7). Plots burned in 2009 or 2010 tended to be cooler than plots burned in 2011
and 2012 (Figure 7). Statistically significant differences were found between 2009
and 2011 (p=0.0051, Appendix A), and 2009 and 2012 (p=0.0138, Appendix A).
Average daily air temperature had a positive correlation on average subsurface
temperature (R2=0.7434, p<0.0001, Appendix C). This was a very strong correlation,
with average air temperature accounting for approximately 74% of the variation in
subsurface temperature.
Within-plot variation in subsurface temperatures did not vary significantly
among burn years (F(3,4)= 0.3013, p=0.8241). Standard deviation of subsurface
temperature only ranged between 0.03°C and 1.15°C throughout the study, likely due
to the increased insulation provided by moss and thatch layers and less influence from
sunlight compared with surface temperatures. Average daily air temperature was not
significantly correlated with subsurface temperature standard deviation (R2=0.0039,
p=0.4416, Appendix C).
32
LSM Average Plot Subsurface Temperature
14
2009 A
2010 A B
12
F(3,4)=8.891, p=0.0185
2011 C
2012 B C
Temperature (°C)
10
air temp
8
6
4
2
0
15-Jan
25-Jan
4-Feb
14-Feb
24-Feb
5-Mar
15-Mar
25-Mar
4-Apr
Figure 7: Results from a repeated measures ANOVA for average subsurface
temperature compared with burn year represented by least squares means
(F(3,4)=8.891, p=0.0.0185). Years are coded as follows: 2009 (green), 2010 (orange),
2011 (red), and 2012 (blue). Average air temperature is shown as a dotted black line.
Soil Moisture
Soil moisture ranged from 34-42% in February and 37-53% in March. No distinct
linear relationships between soil moisture and burn year were found (Table 3);
however, a t-test demonstrated that soil moisture in March was significantly higher
than soil moisture in February (difference=9.721%, p<0.0001).
33
Discussion
Temperature
Observations made over the course of this study demonstrate a significant influence
of a burn chronosequence on both surface and subsurface temperature. Areas last
burned in 2009 were significantly cooler than other burn years during the winter
season. These observations support the estimated historic prairie fire return interval of
every 2-5 years. Approximately four years post-burn, microclimate conditions vary
significantly, and may not provide a warmer temperature advantage to sensitive
species of concern.
Moisture
The burn chronosequence was unexpectedly not correlated with soil moisture.
Anecdotal observations suggest that small topographical variations have a
surprisingly large influence on soil moisture. Furthermore, typical fire influences on
soil that limit water infiltration, such as altered water repellent layers and collapsing
soil structures (Neary et al. 1999), may be less apparent on the already shallow, welldrained, rocky soils of Puget lowland prairies (Dunwiddie and Bakker 2011).
Overall Trends
Observed temperatures demonstrated the anticipated pattern that regular short-interval
burning in Puget lowland prairies provides improved habitat and microclimate
conditions for sensitive species. Differences between burn years became more
apparent over the course of this study. As the growing season begins, we expect these
34
differences to become even more pronounced. The influence of sunlight was very
apparent, accounting for nearly half of the variation in surface temperature recorded
by dataloggers (Figure 6). The increase in available sunlight during the spring and
summer months may provide an increase in temperature variation along the burn
chronosequence. Similar temperature patterns were found in other fire-dependent
grassland ecosystems in southeastern Australia (Bradstock and Auld 1995), South
Africa (Snyman 2003), and the eastern U.S. (Iverson 2005). Observations from this
study suggest that maintaining a fire return interval of four years or less in Puget
lowland prairies provides warmer temperatures that may provide an advantage for
butterfly larvae.
Study Limitations and Future Research
In order to better evaluate the variation of soil temperature and moisture within each
burn year, an increased number of plots spread throughout larger burn areas may be
more representative. Although there was not a significant difference in temperature
standard deviation among burn years, the variation within each plot was still large
enough to imply that larger sampling areas may be more representative of landscapelevel conditions. Employing continuous measurements throughout the landscape may
also capture temporary increases in temperature due to sunbreak variations. Because
species, such as the Taylor’s checkerspot butterfly, are extremely sensitive, even short
variations in temperature throughout the day can mean the difference between a
sustainable, healthy butterfly population and a waning population. Such variations
may not be appropriately represented through snapshot measurements.
35
Recommendations
One of the biggest challenges to prairie restoration is difficulty evaluating
microclimate conditions across the landscape, information important for maintaining
sensitive and rare species. Differences in soil temperatures may result in important
heterogeneity for butterfly survival. Increased variation provides more opportunity for
vulnerable butterflies to appropriately thermoregulate, escape from predators, and
find food and host plants. Fire return intervals providing the most opportunity for
butterflies to utilize a variety of habitat characteristics may then become a primary
management objective to optimize entire prairie locations. Reestablishing successful
populations of this sensitive species may indicate where other prairie-dependent
species will be successful. Based on observations from this preliminary study,
maintaining a fire return interval of approximately four years provides for the
warmest microclimate temperatures for wintering butterfly species. After butterfly
release, maintaining this interval may provide crucial habitat characteristics that
support sustainable populations.
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38
Chapter 3 – Project Significance and Interdisciplinary Connections
Extended Discussion
Surface Temperature
Observations made over the course of this study demonstrate a significant
relationship between surface temperature and a burn chronosequence. Areas burned
in 2009 had significantly cooler surface temperatures than other burn years, a
relationship demonstrated both by average temperatures and maximum temperatures.
The general pattern observed was an increase in surface temperature for more
recently burned areas; however, the only statistically significant differences were
observed between 2009 and other burn years (Appendix A). This pattern appeared to
be stronger in March compared with January, which may imply that as the growing
season proceeds, the influence of the fire chronosequence on temperatures will
become more pronounced. Because light intensity accounted for approximately 47%
of the variation in surface temperature (Figure 6), increased sunlight during the spring
and summer may further influence these temperature differences (Weiss et al. 1988).
Recommendations based on study observations indicate that a fire return
interval of four years is appropriate to maintain warmer microclimates. This may be
especially important for the Taylor’s checkerspot butterfly during the diapause and
post-diapause larval stages, approximately lasting from December through the end of
March (Stinson 2005). If areas that are not being burned more often than four years
provide colder habitats, butterfly larvae may not be getting the temperature advantage
they require for survival. If these temperature patterns continue throughout the
growing season, the success of reproducing adults may be compromised several years
39
after burning if there are insufficient temperatures for thermoregulation (Weiss et al.
1988, Severns 2007, Beyer and Schultz 2010).
Relationships between soil temperature and burning have been more
pronounced in other similar fire-dependent ecosystems. Soils in eastern U.S. forests
maintained warmer daily soil temperatures in burned areas compared to unburned
plots for several months post-fire (Iverson 2005). The South African bush, another
grassland-based ecosystem, showed higher surface temperatures up to two years postburn compared with unburned areas (Snyman 2003). In Snyman’s (2003) study,
however, the strongest patterns between temperature and burning were found during
the growing season. The season of this study, from January to March, concluded at
the start of the growing season for Puget lowland prairies. The relatively small,
nevertheless significant, patterns found over the winter season may become more
pronounced through year-long observations.
Subsurface Soil Temperature
Average subsurface soil temperatures were warmer in recently burned plots than
those burned in earlier years. The indirect influence of subsurface temperatures on the
plant community is imperative for the survival of butterfly larvae. Warmer
microclimates typically provide earlier germination and early senescence of butterfly
host plants (Weiss et al. 1988). Larger differences in subsurface temperature among
burn years were found compared with those seen in surface temperature. Increased
plot-level replication would improve our understanding of the effects of burn history
on soil temperatures.
40
Subsurface temperatures varied less than surface temperatures throughout the
season, likely due to increased insulation from layers of moss and thatch. Moss and
thatch layers are found throughout Puget lowland prairie landscapes, with Johnson
and Upper Weir being no exception. Moss provides insulation for the soil and reduces
the warming impacts from sunbreaks. While fires often alter and destroy these layers,
much of the thatch in the study sites appeared intact throughout the burn
chronosequence. Seasonality of a burn alters the intensity of a burn (Knapp and
Keeley 2006) and lower intensities often create reduced and patchy burns (Augustine
and Milchunas, 2009). For example, the 2012 burn plot on Johnson prairie had
distinct thatch patches remaining after being burned. Areas with remaining thatch also
appeared to have lost less of their moss layer. Replicate plots accounting for various
burn seasons for each burn year may demonstrate stronger patterns in subsurface soil
variation. In other ecosystems, burn season has had a large influence on fire effects.
Post-fire soil temperatures in southeastern Australia varied strongly with burn season,
with a summer burn having significantly higher subsurface soil temperatures
compared with a winter burn (Bradstock and Auld 1995). These differences were
large enough to influence germination rates of legume species, as only the summer
burn had warm enough post-burn temperatures to break seed dormancy. Compared to
a case study following a bush fire in South Africa, subsurface temperatures deeper
than 200 mm also did not demonstrate significant variation between burned and
unburned areas; however, differences in shallower soil temperature appeared stronger
during the growing season (Snyman 2003).
41
Measurements in Johnson prairie and Upper Weir prairie were observed
during the winter season. While differences in temperature were found during this
timeframe, variation in temperature may become more pronounced when investigated
over the growing season, or throughout an entire year. Because post-burn subsurface
temperatures can vary strongly enough in other systems to alter seed germination,
further investigation of this pattern in Puget lowland prairies is still warranted.
Soil Moisture
Although soil moisture ranged from 34-42% in February and 37-53% in March, this
variation was unexpectedly not significantly influenced by burn year. Variation
within plots, as represented by standard deviation, also did not vary significantly
among burn years. The shallow soil of remaining Puget lowland prairies is rocky and
well-drained (Dunwiddie and Bakker 2011), providing a challenge for measuring soil
moisture. The strongest differences in winter soil moisture may only be apparent
immediately following rain events, as water may drain more quickly from recently
burned areas. In other fire-prone ecosystems, more distinct patterns between soil
moisture levels and burning have been found; soil moisture across an entire landscape
in interior Alaskan forests proved significantly higher at a site that had been burned
five years earlier than the control (Kasischke et al. 2007). Long-term fire influences
on Mediterranean soils included lower soil moisture levels and variation in waterrepellent layers (Granged et al. 2011). Due to the minimal variation in soil moisture
within each 40 m2 plot at both Johnson prairie and Upper Weir prairie, we would
recommend sampling moisture across a larger surface for each burn year. The well-
42
draining, rocky soils of Puget lowland prairies make soil moisture challenging to
evaluate. We would expect that further studies may indicate that overall soil moisture
is similar across burn years, but recently burned areas with less vegetation and more
heavily altered soil composition would drain moisture at an accelerated rate.
Extended Future Research
In order to better evaluate the variation of soil temperature and moisture within each
burn year, an increased number of plots spread throughout larger burn areas may be
more representative. Although there was not a significant difference in temperature
standard deviation among burn years, the variation within each plot was still large
enough to imply that larger sampling areas are needed.
Continuous monitoring of temperature may capture the highly variable effects
of sunlight and other weather variations. Snapshot measurements may lack the ability
to capture more extreme differences across the prairie landscape. Daytime surface
temperatures (as recorded by HOBO dataloggers placed on the prairie surface) varied
by as much as 14°C in 30 minutes. This wide-ranging variation is due to rapid
temperature increases during sunbreaks. Observations from infrared thermometers
could detect increases in surface temperature of 6°C or more in only a few seconds
during a sunbreak. Because sampling across plots takes a considerable amount of
time, variation in solar radiation caused by intermittent sunbreaks may have
confounded average temperature differences across spatial scales. Midday
temperatures did demonstrate differences between burn years, but recording average
temperature throughout the entire day may better capture more dynamic changes in
43
blackened soil. Continuous measurements may also better reflect species needs
because some species are sensitive enough to react to small variations that would go
unnoticed in a single daily measurement of microclimatic conditions. Short temporary
differences in temperature due to sunbreaks may provide more opportunity for
butterflies to appropriately thermoregulate.
Further replication of plots across all burn years may reduce impacts from
topographical variation. Puget lowland prairies have widespread topographical
variation. While plots were chosen to utilize relatively flat areas, the variability in
minor slopes and aspects across Johnson prairie and Upper Weir prairie may have
influenced temperature and moisture differences. Distances between plots were
minimized when possible; however, the Johnson prairie 2009 plot and the Upper
Weir prairie 2010 plot were located farther away from other plots due to the burn
mosaic patterns (all plots were located within approximately 100 m of another plot,
with the exception of Johnson 2009 and Upper Weir 2010 which were approximately
200 m from the nearest plot).
The nested impacts of burn season within each year may demonstrate more
variation in temperature and moisture. Varying weather conditions impact the
intensity and behavior of prescribed burns; changes in season lead to changes in burn
effects. Cooler, more humid burns in spring tend to have less intensity than burns
during the hotter and drier summer (Knapp and Keeley 2006). As seasonal conditions
change, fire behavior varies significantly, with varying residence times for critically
high burn temperatures (Savadogo et al. 2012). For Puget lowland prairies, this
translates into differences in thatch, moss, and plant cover in accordance with burn
44
season. However, burn season was unable to be accounted for in this study due to
insufficient records. In addition to burn season, burn history may influence the
recovering community. Depending on how frequently an area was burned, there may
be corresponding changes in fire behavior and fire influences. Variation in recovery
time between burns will further increase heterogeneity across prairie landscapes,
influencing plant communities, thatch levels, and moss layers.
Future studies should continue to evaluate microhabitat conditions specific to
sensitive species. Microclimate is crucial to butterfly survival at all life cycle stages.
One of the benefits of prescribed fire is that it can cover a large section of landscape
relatively quickly; the challenge is how to maximize the amount of necessary
microclimate for butterfly survival. Measuring temperature and moisture along a
scale of tens of meters across an entire ecosystem is not often an efficient use of
resources, and smaller scale projects are difficult to generalize across larger scale
prairies. The highly fragmented nature of Puget lowland prairies lends to enormous
variation among habitat sites. Because it contains the largest, most continuous, and
most pristine of the remaining Puget lowland prairies, Joint-Base Lewis-McChord has
the potential to create the standard for prairie restoration success. Some of the few
remaining natural Taylor’s checkerspot butterfly populations are found on the base,
implying that there must be some habitat quality there that is providing opportunity
for survival. Restoring the unique ecological functions provided by rare species is
crucial to restoring the few remaining Puget lowland prairie ecosystems. Our advice
to future projects would be to utilize continuous measurements whenever possible
and attempt to characterize variability in microhabitats for keystone species.
45
Restoration Impacts
The rarity of Puget lowland prairies unfortunately means a lack of quantitative
evidence to support anecdotal ecological patterns (Dunwiddie and Bakker 2011).
Studies designed to test observed and assumed patterns are important to influence
management practices. Prescribed burning needs to be used effectively, as there is not
much prairie land left to lose to mistakes. This study is one of the first to directly
measure temperature changes in the Puget lowland prairies, and it will serve as a pilot
study for further research. An important consideration for future studies is long-term
landscape characteristics. Throughout the succession of an ecosystem post-fire, the
beneficial influences of fire begin to fade. Increases in moss and thatch cover, along
with increased cover of non-native plants, can diminish the habitat quality for prairiedependent species. In the sensitive Puget lowland prairies, frequent burning may
maintain essential ecological function by maintaining appropriate soil microclimate
conditions. Many restoration goals can be met by maintaining a fire return interval
that maximizes a diversity of beneficial effects for the longest amount of time.
Fire management plans need to adapt to a number of challenges with regard to
predicting and utilizing fire influences. Variation in landscape, weather, and
seasonality are all characteristics that influence fire effects. Adaptive management is
especially important when utilizing fire disturbances for endangered species. Altering
the plant community through regular burning and maintaining long-term temperature
increases affects all prairie wildlife. In addition to the Taylor’s checkerspot butterfly,
another candidate species for protection under the Federal Endangered Species Act,
(ESA) the streaked-horned lark (Eremophila alpestris strigata) thrives on open
46
habitat created by burning (Pearson and Altman 2005, Stinson 2005). Increasing open
habitat and native forb diversity also benefits the Mazama pocket gopher (Thomomys
mazama), a third ESA candidate species (Stinson 2005). For a landscape as
topographically variable and fragmented as the remaining Puget lowland prairies,
adaptive management and feedback learning are valuable restoration strategies for
understudied rare species. Adjusting to new research-based information on fire
influences is crucial to endangered species restoration as well as improving human
safety and reducing catastrophic fire potential (Stephens and Ruth 2005).
Adaptive management can also be utilized to improve ecological resilience.
Long-term fire suppression in historically fire-dependent ecosystems may hinder the
ability of those systems to recover from disturbances. Frequent, low-intensity fires
allow plant and wildlife species to adapt and build stronger defenses against future
fires. Ecological resilience is especially important as climate change potentially alters
fire behavior and plant communities. Degradation of prairies may be exacerbated
under new climate conditions; however there is also the possibility of prairie
expansion into former agricultural and forest lands in a new climate regime (Bachelet
et al. 2011). The potential expansion of prairies may force human populations to
manage lands for resiliency against regular fire influences.
Stakeholders
A variety of stakeholders are involved in and influenced by restoration practices in
Puget lowland prairies. The fragmented nature of this habitat means prairies are found
on private, state, and federal lands. Private landowners are not required to participate
47
in management practices; however, they are impacted by federal legislation if
candidate species are granted protection under the federal Endangered Species Act (as
of the date of this thesis, Taylor’s checkerspot butterfly and Mazama pocket gopher
are proposed federally endangered species, and the streaked-horned lark is a proposed
federally threatened species). The prairies found on Joint Base Lewis-McChord are
often considered the most pristine of the remaining habitat, which creates a rather
unique concern. Management of these areas is a concern for both ecological reasons
and to maintain military training. Classifying species as endangered impacts the
training strategies of the military; for some of the candidate species, the few
remaining successful populations exist almost exclusively on military property. The
United States Department of Defense has become an enormously influential
stakeholder with their financial power and physical means to maintain the prairies
that exist on their property as well as a strong motivation to establish healthy wildlife
populations and high-quality habitat in other locations. Ironically, military training
involving explosives is likely the reason why the most pristine prairies are found on
the base; while other areas were highly impacted by fire suppression, regular fires still
occurred on military property. Joint Base Lewis-McChord provides ample learning
opportunities for ecologists and land managers to define high-quality prairies. While
sensitive species-of-concern still persist, observations of optimal habitat attributes can
create standards for restoring other prairie areas that historically also housed these
species. In addition to military interest, several non-profit organizations and private
landowners are important stakeholders. Collaboration between stakeholders,
including the Department of Defense, the Center for Natural Lands Management, the
48
Department of Natural Resources, the Evergreen State College, and others, has
increased collective understanding of Puget lowland prairies through quantitative and
qualitative research and management. Partnerships with private landowners have also
increased available land for prairie restoration and conservation, providing
opportunities to increase connectivity between available prairie habitat locations.
Interdisciplinary Practices
Successful restoration and management of any ecosystem requires effective
interdisciplinary work. Fire ecology requires knowledge of multiple disciplines to
truly understand the impacts fire has on a landscape, including: soil science,
chemistry, botany, wildlife ecology, climatology, physics, human health and safety,
economics, entomology, and more. Collaboration between these various disciplines
improves fire management success in maintaining the ecological benefits of fire while
still providing for human health and safety.
Impossible to ignore are the economic impacts of fire disturbances.
Regardless of whether the policy for an area is full suppression of every wildfire or
routine use of prescribed fire, there is a financial cost. Economic costs come from
hiring personnel, damaged property, lost natural resources, and health-related issues.
Firefighters require specialized training and personal protective equipment for their
own safety, as well as equipment such as fire trucks, hoses, and water pumps. The
financial burden of this equipment often falls upon state budgets. Fire suppression
practices were implemented in the United States in the 1930s because of the desire to
not only save lives but also to save resources (Dombeck et al. 2004, Jensen and
49
McPherson 2008). In the Pacific Northwest, many communities depend on logging
and timber industries to provide employment opportunities. Forest fires were thought
to destroy valuable timber products and have even contributed to unemployment in
entire towns (Noss et al. 2006). Interestingly, fire suppression practices often cost
more than the resources that would have been lost if the fire was left to burn on its
own (Jensen and McPherson 2008). Encouraging lower intensity fires may have
actually benefitted timber industries by improving tree and ecosystem health and
function.
Maintaining defensible property in the wildland-urban interface has a personal
cost to private landowners. Costs associated with personal property protection,
including insurance, tools, and appropriate landscaping, merit consideration. Another
large financial burden is the ecological consequence of years of fire suppression. As
fire-dependent ecosystems, such as the Puget lowland prairies, are deprived of fire
disturbances, management costs increase and sustainable practices become more
difficult to achieve (Brooks et al. 2004). As these ecosystems are altered and become
rare, so do the species that depend on them. Species that are granted endangered or
threatened status under the Federal Endangered Species Act bring on additional
protective costs. Managers need to protect remaining populations and preserve
habitat. In turn, private landowners also become responsible for federally endangered
species if populations exist on their property. Economic incentives, such as fines or
increased management costs, can shape human behavior in ways that may actually
inhibit endangered species recovery (Shogren et al. 1999).
50
Social concerns that impact fire policy include public health and safety. Even
controlled prescribed fires have inherent unavoidable risks (Stephens and Ruth 2005).
Unpredictable fire behavior can lead to lost lives and damaged property. Especially in
very dry and windy conditions, fires can travel very quickly. A fire a mile away can
suddenly be at your door in minutes. While wildland fire-fighting knowledge and
experience have increased over the last few decades, one of the most important
lessons learned is that fire can be very unpredictable. The timing of evacuation orders
for people living within the wildland-urban interface is crucial to save lives (Cova
2005). Flames can travel quickly, and smoke can block visibility on roads.
Cooperation of ecologists, public officials, fire-fighters, and residents is needed for
effective evacuations, public education, and maximum protection of human lives.
Even if a nearby fire is not a direct threat to a community, nuisance smoke
from both wildfires and prescribed fires can create serious health problems, especially
in sensitive populations. Inhalation of small particulate matter can create breathing
difficulties (Bowman and Johnston 2005). Smoke can contain a variety of noxious
chemicals that have the potential to cause health damage. Carbon monoxide exposure
can lead to headaches, and in extreme cases death (Reinhardt and Ottmar 2000).
Communities that are particularly susceptible to regular fires also require appropriate
medical facilities to manage those who are impacted by smoke inhalation or burns
(Cova, 2005). Firefighters are at the highest risk of having severe health issues due to
their close proximity to flames and smoke. The safety of firefighters, as well as their
success at controlling a fire, depends on shared knowledge of weather predictions and
51
ecological conditions. Regardless of the fire policy, humans and their property are put
at risk with both anthropogenic fires and wildfires.
Political challenges are often created by concerns for public safety and
financial costs. Fire management policies need to simultaneously protect the welfare
of people and property within management areas, the economic stability of affected
communities, and ecosystem services. These issues create a considerable need for
interdisciplinary cooperation when prescribed burning is proposed. Obvious concerns
about the safety of surrounding communities and firefighting personnel may make
intentional fires seem unnecessarily dangerous at first glance. However, prescribed
burning places personnel at a considerably lower risk than fighting wildfires, and
provides control over when and where a burn occurs to utilize optimal weather and
environmental conditions. By reintroducing smaller, controlled, and less intense burns
into fire-dependent systems, the risk of catastrophic and unpredictable wildfires is
greatly reduced. Justifying the risks of prescribed burning through the ecological,
social, and financial benefits gained by better protecting ecosystems from
catastrophic wildfires is the challenge for ecological burn managers. Nevertheless,
negative media attention, as well as the conspicuous nature of fires, often challenges
public acceptance prescribed burning.
Fire Ecology and Sustainability: Case Studies
Embracing fire disturbances in historically fire-dependent ecosystems promotes
environmental, economic, and cultural sustainability. A prime example of sustainable
fire practices occurs in Kruger National Park, South Africa. Kruger National Park
52
relies on mosaic burning to maintain habitat for elephants, leopards, and other
sensitive species. As part of a management plan, fire has helped restore African
elephant (Loxodonta africana) populations, improving their IUCN (International
Union for Conservation of Nature) red list category from “endangered” to
“vulnerable” in 2004 (Blanc, 2008). Wildlife adaptations to regular fire disturbances
become apparent within days of a burn. Emergent grass shoots attract grazing
animals, such as zebras. The improved habitat within Kruger National Park also
serves the important function of containing large and dangerous animals. Preventing
animals from damaging crops, destroying property, and threatening human safety
protects local communities and economics interests. Fire regimes create strong
connections between environmental, social, and economic sustainability that are
crucial to maintaining coexistence between humans and wildlife at Kruger National
Park.
Fire ecology also helps create sustainability in farming communities. In South
America, charcoal is used as an inexpensive, environmentally-safe form of fertilizer
(Glaser 2007). Economically, farmers benefit from increased agricultural yield after
supplementing soil with ash (Glaser 2007). While intensive farming depletes soil
nutrients, using charcoal as a soil amendment in conjunction with other sustainable
practices can be particularly effective in maintaining soil fertility (Glaser 2007). The
improvement of agricultural yields through burning and charcoal soil amendments
can also increase social capital in farming communities by providing a means to
maintain trade connections and cooperation (Glaser 2007). Furthermore, increased
food availability may improve public health (Glaser 2007). In addition to facilitating
53
sustainable agricultural practices, charcoal fertilizer can contribute to nutrient
availability in restoration areas (Barrow 2011). The utilization of charcoal may also
have global implications. Long-term atmospheric carbon dioxide sequestration can
occur through the creation of charcoal (Barrow 2011). Embracing this aspect of fire
improves sustainability on several scales: higher agricultural yields locally, reduced
environmental degradation regionally, and atmospheric carbon dioxide mitigation
globally
Reintroducing the historic fire regime to Puget lowland prairies is an
opportunity to preserve Native American heritage. Historically, prairies provided
indigenous food crops, such as camas (Camassia quamash, USDA NRCS 2013)
bulbs (Walsh et al. 2010). Native populations used fire as a hunting strategy;
anthropogenic burning created habitats attractive to large game and edible insects
(Shinn 1980). Furthermore, burning opened landscapes and decreased the effort
required to acquire game. Anthropogenic prairie fires also played a role in social
interactions between tribes. Tribes used fire as a signal for organizing convocations or
migrations (Shinn 1980). Native populations also used anthropogenic fires as a war
tactic to create a barricade against enemies (Shinn 1980). Whether in South Africa,
South America, or the west coast of the United States, prescribed burning has
enhanced the environmental, economic, and cultural sustainability of local
communities.
54
Conclusion
Increasing available prairie habitat in the Pacific Northwest will hopefully increase
the spread and success of endangered species, and decrease their need for federal
protection. It is crucial to gain stakeholder cooperation in order to reduce the
management requirements, financial costs, and ecological costs of species decline.
Every ecological dilemma needs to consider social, political, and economic
components to improve the health, resilience, and sustainability of ecosystems. For
many communities, fire can play an important ecological role that can provide a more
sustainable lifestyle.
55
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Appendix A: Contrast Pairwise Comparison Results
63
62
61
2012
2010
60
Canonical1
59
pair
2009
2011
2009
2010
2009
2011
58
Grand
57
56
55
54
2012
2012
2010
2011
2011
F
72.7548
4.1168
61.1599
1.7419
42.2584
p
0.001
0.1123
0.0014
0.2574
0.0029
53
2009
52
51
-6 -5 -4 -3 -2 -1 0
1
2
3
4
5
6
Canonical2
Figure A1: Pairwise contrast results for average surface temperature. Bolded rows
indicate significant differences. A Bonferroni correction indicated that p-values less
than 0.01 were significant.
39
38
2012
37
36
Canonical1
pair
2009
2011
2009
2010
2009
2010
2011
82
89
63
67
46
75
32
18
42
53
25
Grand
35
34
33
F
27.8496
0.8244
19.7474
0.0056
19.0884
p
0.0062
0.4152
0.0113
0.9440
0.0120
2009
32
31
-4
2012
2012
2010
2011
2011
-3
-2
-1
0
1
2
3
4
Canonical2
Figure A2: Pairwise contrast results for maximum surface temperature. Bolded rows
indicate significant differences. A Bonferroni correction indicated that p-values less
than 0.01 were significant.
62
55
2011
54
2012
88
81
67
63
25
46
32
74
18
42
Grand
Canonical1
53
52
pair
2009
2010
2011
2009
2010
2009
2010
51
50
2009
49
-3
-2
-1
0
1
2
2012
2012
2012
2010
2011
2011
F
17.5489
4.3872
1.8796
4.3872
12.0102
30.9152
p
0.0138
0.1043
0.2423
0.1043
0.0257
0.0051
3
Canonical2
Figure A3: Pairwise contrast results for maximum surface temperature. Bolded rows
indicate significant differences. A Bonferroni correction indicated that p-values less
than 0.01 were significant.
63
Appendix B: Sample Datalogger data
Midday Moving 5-day Average Temperature
Johnson Prairie
18
2009
16
2010
2011
14
2012
air temperature
Temperature (°C)
12
10
8
6
4
2
0
20-Jan
25-Jan
30-Jan
4-Feb
9-Feb
14-Feb
Figure B1: Sample 5 day moving average surface temperature (recorded from
dataloggers) from Johnson prairie from January 19th to February 14th 2013. Average
air temperature was recorded from Ft Lewis weather data
(http://www.wunderground.com/history/airport/KGRF/2013/2/15/DailyHistory.html?
req_city=NA&req_state=NA&req_statename=NA).
64
Midday Moving 5-day Average Temperature
Upper Weir Prairie
18
2010
16
2011
2012
14
2013
air temperature
Temperature (°C)
12
10
8
6
4
2
0
17-Feb
19-Feb
21-Feb
23-Feb
25-Feb
27-Feb
29-Feb
Figure B2: Sample 5 day moving average surface temperature (recorded from
dataloggers) from Upper Weir prairie from February 16th to March 3rd 2013. Average
air temperature was recorded from Ft Lewis weather data
(http://www.wunderground.com/history/airport/KGRF/2013/2/15/DailyHistory.html?
req_city=NA&req_state=NA&req_statename=NA).
65
Appendix C: Average Daily Air Temperature Influence
Influence of Average Daily Air Temperature on Average Surface Temperature
35
2
R = 0.1875, p<0.0001
Average Surface Temperature (°C)
30
25
20
15
10
5
0
0
-2
2
4
6
8
10
12
14
Average Daily Air Temperature (°C)
Figure C1: Regression analysis of the influence of average daily air temperature on
average surface temperature. Air temperature has a significant positive influence on
surface temperature, accounting for approximately 19% of the variation (R2 = 0.1875,
p<0.0001).
Influence of Average Daily Air Temperature on Maximum Surface Temperature
40
R2 =0.1292, p<0.001
Maximum Surface Temperature (°C)
35
30
25
20
15
10
5
0
-2
0
2
4
6
8
10
12
14
Average Daily Air Temperature (°C)
Figure C2: Regression analysis of the influence of average daily air temperature on
maximum surface temperature. Air temperature has a significant positive influence on
surface temperature, accounting for approximately 13% of the variation (R2 = 0.1292,
p<0.0001).
66
Influence of Average Daily Air Temperature on Surface Temperature Standard
Deviation
4.5
2
R =0.0123, p=0.1451
Surface Temperature Standard Deviation (°C)
4
3.5
3
2.5
2
1.5
1
0.5
0
0
-2
2
4
6
8
10
12
14
Average Daily Air Temperature (°C)
Figure C3: Regression analysis of the influence of average daily air temperature on
surface temperature variation within each plot, represented by standard deviation. Air
temperature did not significantly influence surface temperature variation (R2 =
0.0123, p=0.1451).
Influence of Average Daily Air Temperature on Average Subsurface Temperature
16
R2 = 0.7434, p<0.0001
Average Subsurface Temperature (°C)
14
12
10
8
6
4
2
0
-2
0
2
4
6
8
10
12
14
-2
Average Daily Air Temperature (°C)
Figure C2: Regression analysis of the influence of average daily air temperature on
average subsurface temperature. Air temperature has a significant positive influence
on surface temperature, accounting for approximately 74% of the variation (R2 =
0.7434, p<0.0001).
67
Influence of Average Daily Air Temperature on Subsurface Temperature
Standard Deviation
Subsurface Temperature Standard Deviation (°C)
2.5
2
R = 0.0039, p=0.4416
2
1.5
1
0.5
0
-2
0
2
4
6
8
10
12
14
Average Daily Air Temperature (°C)
Figure C3: Regression analysis of the influence of average daily air temperature on
subsurface temperature variation within each plot, represented by standard deviation.
Air temperature did not significantly influence subsurface temperature variation (R2 =
0.0123, p=0.1451).
68