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Don Falk, Tom Swetnam & Chris BaisanDon Falk, Tom Swetnam & Chris BaisanLaboratory of TreeLaboratory of Tree--Ring ResearchRing Research

The University of ArizonaThe University of Arizona

Fire History and Climate Fire History and Climate Variability in Forests of Variability in Forests of

Southwestern North Southwestern North AmericaAmerica

ECOL 206 (Environmental Biology), Spring 2005

Main themes:

• Fire is a natural and essential ecosystem process in many forest systems

• Vegetation and climate largely govern fire regimes

• Human land uses have altered fire regimes in the region, with cascading effects

How do we understand fire as an ecosystem process?

• Observe contemporary events (fire behavior and fire effects)

• Reconstruct historical ecosystem dynamics (fire and climate history)

• Model fire-climate-vegetation interactions (ecological modeling)

What we observe: large, high-intensity fires

Aspen Fire, Catalina Mountains, June 2003 Rodeo-

Chedeski Fire June 2002

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Hi Meadow, CO 4,422 ha

Viveash, NM 11,017 ha

Bobcat Gulch, CO 3,059 ha

High burn

Low/Unburned

Courtesy N. Kotliar, USGS 34

Year1940 1950 1960 1970 1980 1990

01000020000300004000050000

0

20000

40000

60000

80000Region 1 Northern RockiesRegion 6 Washington & Oregon

Region 3 Arizona & New Mexico

1956

1973& 1974

1988 & 1989

Area Burned on National Forests inPacific Northwest (Regions 1 & 6) & American Southwest (Region 3)

1945 to 1990

Central question: Are these large and impressive fires within or outside the range of natural variation?

Photo in R. S. Kellogg 1902, Forest Conditions in Southern Arizona. Forestry & Irrigation 8:501-505.

Forest and fire history provide insight into such questions

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190919491990

Biondi, F. 1999. Ecological Applications 9: 216-227

Lightning strike frequency in Saguaro National Park, Rincon Mountains, Arizona

Wilderness

Park

National

Saguaro Mountain

Rincon

Tanque VerdePeak

8613Mica Mtn

Rincon Pk8483

Chim

enea Canyon

Rincon

Valley

Wilderness

3 0 3 Kilometers

Lightning Density From 1989 to 1999

Contour Interval = 100m

Strikes / 1000 ha11 - 1314 - 1617 - 1819 - 2122 - 2324 - 2627 - 2829 - 3132 - 3334 - 36

~3 strikes /km2/year

Courtesy of Calvin Farris

Some salient attributes of the tree-ring record

• Wide spatial distribution (> 130ºglobal latitudinal range)

• Record wide array of ecological variables

• Long temporal extent (≥104 yr) and preservation

• High temporal resolution (10-1

yr) and accuracy (exact, if crossdated)

• Direct, affirmative evidence of ecological events

“Sky Island” Mountain Ranges with Fire Scar Fire Histories:

Santa Catalina

Rincon

Santa Rita

Huachuca

Pinaleños

Chiricahua

Sierra de los Ajos

Animas

Mogollon

White

Southwestern US Fire-Scar Network

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1

3

4

1. East Cascades, 2 watersheds, 723 trees, Everett et al. 1999, For. Ecol. & Manage., In press.

2. Blue Mountains, 4 watersheds, 628 trees, Heyerdahl 1998 PhD diss., Univ. Wash.

3. West Slope Sierra Nevada, 4 elevational transects, 49 sites, 446 trees, Swetnam & Baisan, In Press.

4. Southwestern US, 63 sites, 1,215 trees, Swetnam and Baisan 1996, USFS RM-GTR-286:11-32.

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Extensive Fire-Scar Networks in the western U.S

90 fire scarred trees sampled in 2 stands

Composite fire record for Monument Canyon RNA, Jemez Mountains, New Mexico

Fire scar chronology from pine/mixed conifer on Mount Graham

Fire-scar chronology from Gila Wilderness, in Southwestern New Mexico. Livestock & Fire

Suppression Era19th Century Fire Gap

Swetnam and Baisan 2003Kaib 1998, and Seklecki et al. 1996

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Large aspen stands in the Southern Rockies are typically a Large aspen stands in the Southern Rockies are typically a ““footprintfootprint”” of past crown fires. Margolis, Swetnam & Allen, of past crown fires. Margolis, Swetnam & Allen, in prep.in prep.

Fire history in high-severity, stand-replacing ecosystems

NM/CO Border

1861

Alamosa, CO

Albuquerque, NM

1861

1851

Death dates of Death dates of firefire--killed killed snagssnags

Recruitment dates Recruitment dates of postof post--fire aspenfire aspen

Margolis et al, in prep.Margolis et al, in prep. 1840 1850 1860 1870 1880 1890 1900

Per

cent

age

of S

ites

Rec

ordi

ng F

ire

0

10

20

30

40

50

60regional surface fire yearstand-replacement fire year

Synchronous crown fire years in northern NM and southern CO are coincident with regional surface fire years in the Southwest.

Margolis et al., in prep.

The role of climate as a governing factor for fire regimes:

• Decadal climate governs the distribution of vegetation• Inter-annual climate variation regulates biomass (fuel) production• Intra-annual (seasonal) climate variation generates “fire weather” that regulates fuel moisture, provides most ignitions, and triggers extreme events

The Southwestern US network of fire scar sites shows a high degree of regional fire synchrony –the largest and smallest fire years are well correlated with dry and wet years, respectively.

Livestock Grazing/Fire Suppression EraSwetnam & Baisan 2003

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Synchronous stand replacing fire years correspond with major drought years.

Margolis et al., in prep.

Drought, fire...what about insect outbreaks?Western spruce budworm extends from British Columbia to the Southwest. Outbreaks encompassing millions of hectares have occurred several times in the 20th century, far exceeding area burned in major fires. Current outbreak in BC > 10 million ha.

The mid-1990s to present drought follows the extraordinary decadal wet period of the mid-1970s to early 1990s.

Courtesy of Kurt Kipfmueller, Univ. Arizona Laboratory of Tree-Ring Research. From Ni et al., 2002

Turn-of-the century drought

1910-20s wet period

1930s to 1960s droughts

1970s-1990s wet period Current

drought

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Multiproxy temperature reconstructions (from tree rings, ice cores, etc.) and simulations global circulation models agree that Northern Hemisphere temperatures in recent decades are at the highest levels in at least 1,000 years.

0

20

40

60

80

100

1900 1920 1940 1960 1980 2000

WESTERN USA DROUGHT TREND: 1900 - 2003

y = -329.72 + 0.185x R= 0.232* p<0.05 2-tailed

YEAR

Dro

ught

Are

a In

dex

(<-1

)

Cook et al. 2004

Observed change in surface temperature for the Southwest US (black line) compared to a global climate model simulation of SW US temperature driven by increasing GHG.

Courtesy Henry Diaz, NOAA.

Multi-model projection of winter temperature and precipitation changes for the Southwest United States. Curves show the temporal evolution as departure from the 1971–2003 averages.

Courtesy Henry Diaz, NOAA.

Dense overgrown forests are a common element in severe fires and

insect outbreaks

Land use: People, forests, and fire on a collision course

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Private Inholdings on the Payson District, Tonto NFGraphic courtesy Tonto NF

• 75 locations within District subdivided into more than 3,000 parcels

• Occupy only 4.7% of acreage but influence management decisions across entire District

Fire fighters in Santa Catalina Mountains, clearing a fire line and swatting low flames with makeshift hand tools - cut tree saplings.

Photo taken in May 1900, by early forest surveyor S. J. Holsinger near Mount Lemmon.

How can we make our forests more resilient to the effects of climate change?

We know:

Fire was ubiquitous in grasslands, woodlands and forests of western North America before ca. 1900, and drastically reduced in frequency and extent thereafter.

Fires were ignited by both lightning and people before and after 1900. The initial disruption of frequent, widespread fire was caused by the introduction of large numbers of livestock.

Increasing forest density and connectivity sets up large high-severity events.

Fire suppression feeds the cycle of large fires.

Inter-annual and decadal climate variability influence fire occurrence now as in the past.

We need to know more about:

Fire frequency estimates from more locations and how they varied in space and time.

The role of Native Americans in altering/influencing pre-1900 fire regimes.

Effects on fire behavior of the combination of forest structure changes and climate.

The effect of greenhouse gas-caused warming on Southwestern climate and wildfire occurrence, including changes in seasonality.

Effects of changing land use in the West, and social acceptance of fire as a landscape presence