Download Mapping Fire Regimes Across Time and Space:

Fire-climate-vegetationtopography-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 (18801999) 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-climatevegetation-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-firevegetation 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
th
20 -Century Fire Perimeters -- Gila/Aldo Leopold Wilderness Areas
New Mexico
1900
1910
1920
1930
1940
1950
20 k
1960
1970
1980
AZ
NM
1990
Fire atlas boundary
Gila NF Wilderness District
Boundary
N
Rollins/LTRR
Area burned during three different eras of
fire management
Area burned and Palmer Drought Severity Index (PDSI)
GALWC
Fire frequency
• Derived from the fire
atlases
• Fires >50 ha
Unburned
Burned Once
Burned Twice
Burned Three or
More Times
SBWA
N
20 k
Gila/Aldo Leopold Wilderness Complex
Mogollon Baldy - Langstroth Mesa Transect
1904
9
1965
15
5
5
1953
1968
5
1992
5
37
1953
1904
10
1989
1938
1992
1986 - 1997 fires per 100 ha
Lightning Ignitions
Human Ignitions
Lightning, fires, topography and vegetation
GALWC, fires/100 ha,1986 - 1997
Lightning ignitions
Human ignitions
Climate from tree rings
Cross-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.nrcanrncan.gc.ca/cfsscf/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