Fire-climate-vegetation-topography-land use

What drives and determines fire patterns across time and space?

What are the implications of global climate change?

Global climate change• Avg. surface T increased by 0.6C in 20th

century

• 1990s were warmest decade and 1998 was warmest year since 1861, and probably the warmest of the last 1000 yr

• Freeze-free season longer in mid and high latitudes

• Less snow and ice, higher sea levels

Global temperatures• Mean global

temperatures in 2000 were 0.39C (0.7F) above the long-term (1880-1999) average

• 2000 was the sixth warmest year on record

• The only years warmer were 1998, 1997, 1995, 1990 and 1999

Earth’s surface temperature, 140 yr

IPCC 2000

Earth’s surface temperature, 1000 yr

IPCC 2000

Global changes in atmosphere• CO2 content has increased by 31% since

1750

• Higher concentration now than at any time in last 420,000 yr, and probably more than at any time in last 20 million yr

• Rate of increase in concentration is unprecedented in the last 20,000 yr

Greenhouse gasses

IPCC 2000

Future changes• Global surface temperature increase by 1.4

to 5.8C between 1990 and 2000

• Land areas will warm more than the oceans, especially northern North America

• Larger and faster changes than at any time in last 10,000 yr

Future climate extremes

IPCC 2000

Climate change and fires• What are the implications for fires

and their ecological effects?• The answer depends in part on the

role of climate vs topography or local fuel conditions in determining fire patterns

• We’ll also look at some of the tools people are using to answer these questions

Example hypotheses

• There are linkages among fire-climate-vegetation-land use-topography across temporal and spatial scales

• Regional climate entrains fire patterns at fine spatial scales, overriding the influence of local topography and vegetation, leading to synchrony at widely separated sites and across regions

• Fires will mediate the effects of climate change

Approaches• Cross-regional studies• Comparative case studies:

thoughtful comparisons across time and space, and in different climates will be informative of general theory

• Simulation models• Long-term climate-fire-

vegetation reconstructions• Combined approaches

Drought

Swetnam, TW

Fire along environmental gradients

Swetnam, TW

• Fire frequency• Fires of some size every few yrs • Larger fires once or twice per decade• Regional fire yrs 2 to 5 times per century

• Synchrony• Variable• Factors controlling fire regimes varied through time• Climate important in controlling landscape conditions and

ignitions• Wet conditions favored increased fuel production and accumulation• Dry conditions favored effective ignition and spread. • Cool/moist decreased fire frequency, but increased fire size and

intensity. • Long-term warm/dry conditions: more frequent fires, but less spatial

continuity of fuels and, consequently smaller fires.

Implications for the future• Fire regimes will continue to change in response to

changing forest conditions and climate• A warmer climate with more frequent burning could

change species composition• Wet, warm climate could increase fuel production,

with corresponding increases in fire intensity and size

• Warmer-drier conditions might lead to intense fires followed by a decrease in fire severity as fuel production declined.

• The forest-climate-fire system is dynamic

Area burned• Selway-Bitterroot Wilderness Area

• 474,237 ha burned in 437 fires from 1880 to 1996• 7 yrs of extensive fire, 72% of all area burned• 1889, 1910, 1919, 1929, 1934, and 1988

• Gila-Aldo Leopold Wilderness Complex• 147,356 ha burned in 232 fires from 1909 to 1993• 6 yrs of extensive fire, 71% of all area burned• 1909, 1946, 1951, 1985, 1992, 1993

Fire atlas boundary

Gila NF W ilderness DistrictBoundary

1900

1910

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20 -Century Fire Perimeters -- G ila/Aldo Leopold Wilderness AreasNew Mexico

th

AZ NM

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Rollins/LTRR

20 k

Area burned during three different eras of fire management

Area burned and Palmer Drought Severity Index (PDSI)

Fire frequency • Derived from the fire

atlases• Fires >50 ha

U n b u rn ed

B u rn e d O n c e

B u rn e d Tw ic e

B u rn e d T h ree o r M o re T im e s

20 k

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SBWA

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19921938

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Gila/Aldo Leopold Wilderness ComplexMogollon Baldy - Langstroth Mesa Transect

1986 - 1997 fires per 100 ha

Lightning Ignitions

Human Ignitions

Lightning, fires, topography and vegetationGALWC, fires/100 ha,1986 - 1997

Lightning ignitions Human ignitions

Climate from tree ringsCross-dating is used to identify missing and false rings, and therefore to get accurate dates

Old trees give longer records

Changing fire patterns

Complex interactions• Fires influence global C

• Fires release CO2

• Fire-killed vegetation decomposes

• Recovering vegetation may absorb less C

• Fires will increase under climate change• Canada may experience a

50% increase in annual area burned (Amiro et al. 2001, Flannigan et al. 1998)

• The number of lightning fires could increase by 30% (Price and Rind 1994)

• Extended fire seasons

Canadian Forest Service. 2001. Forest fire: context for the Canadian Forest Service’s science program. 2001. Available [Online]: <http://www.nrcan-rncan.gc.ca/cfs-scf/science/context_fire/index_e.html>. Accessed November 2001.

Drivers• Local site productivity

• Topography

• Climate

• Fire exclusion policies

• Land use

• Exotic plants

Climate-vegetation-land use linkages• Climate is a major driver of fire occurrence in all fire

regimes, but • Climate and climate variability only partially explains

changes in fire regimes through time • Land use has altered fire regimes: grazing (where

fine fuels carry fires), roads (limit fire spread), fire suppression, logging, mining, exotics, etc.• Intensive grazing in dry forests (Swetnam and Baisan

1996; Swetnam and Betancourt 1990, 1998)• Fire suppression (Rollins et al. in press)• Less influential where infrequent, stand-replacing fires

were the norm• Fire size has not changed in 20th century in chaparral of

CA (Keeley et al. 1999)

What have we learned• Climate has an overriding importance at both

broad and fine scales (Swetnam and Betancourt 1998; Heyerdahl et al. 2001), particularly for extreme events.

• Human impacts are ubiquitous as well, but more pronounced in altering fire regimes where fires were historically frequent (Hardy et al. 2001), and where human population density is high and land use is intense (e.g. chaparral in California, Keeley et al. 1999).

Salmon R. in Idaho, Photo from Amy Haak

Challis National Forest, Idaho, Photo from Amy Haak