DISTURBANCE REGIMES AND DISTURBANCE WINDOWS:
CONTEMPORARY POST-FIRE PHENOLOGY
IN THE BASIN AND RANGE, USA
Joel B. Sankey
U.S. Geological Survey
jsankey@usgs.gov
https://profile.usgs.gov/jsankey
Fire in the Western USA
• Contemporary changes:
– Longer annual wildfire season
– Increase in wildfire frequency
– More big fires
Fires and Erosion
• Contemporary changes:
– Increase in post-fire
erosion of soil
Relative Sediment Transport
(rate/bare surface rate)
1
Water
Wind
0.5
0
0
0.5
Relative Vegetation Abundance
(fractional cover with uniform spacing)
1
CarbonCarbon
discharge
(g C
discha
100
*
100
0
0
B
> 106
*
300
C
> 500
300
-1
-1 -1
-1
Carbon
discharge
(g C(gmC dm) d )
Carbon
discharge
Fires and Erosion
200
200
*
100
100
0
8/07
12/07
4/08
8/08
12/08
-1
-1
d )
> 500
rge (g C m
• Contemporary changes:
– Increased nutrient and
element transport
200
300
Fire
200
Date
(Hasselquist et al., 2012, Biogeosci)
C
Fires and Erosion
•
Contemporary changes:
- Increased nutrient
and element transport
- Local effects
(Sankey et al., 2012, JGR and JAR)
Fires and Erosion
•
Contemporary changes:
- Increased nutrient
and element transport
- Regional effects (e.g., dust on snow)
Great Basin Climate
Short-term post-fire vegetation dynamics
Spring
Fall
Sankey et al.(2009) JAE and JAR
Disturbance Windows: short-term post-fire vegetation dynamics
and soil stabilization
Erosion-limiting
factor
Eroded sediment
yield
Vegetation
Window of disturbance
Fire
Time
(Shakesby and Doerr, 2006)
Short-term, post-fire
windows of disturbance:
potential for especially
large magnitude erosion
events
Disturbance Windows
Vegetation
Greenness
(e.g., NDVI)
Calendar year
Calendar year
Eroded sediment
yield
Calendar year
Fire
Time
Calendar year
Calendar year
Fire Database
Effects of:
- Fire season length
- Seeding treatments
Fire database:
- from USGS-FRESC, USFS
- ~100 historical fires in
sagebrush steppe
- foothills
- loamy ecosites
- seeding treatments
- replicate plots
Seeding
• Long-term goals: Desirable vegetation community
• Short-term goals: Rapid protective cover of vegetation for soil
stabilization
• Very common, expensive, limited follow-up or evaluation
Fire Database
Fire Database
Mallard Lake F494
Fire Database
Remote Sensing Phenology MODIS NDVI 16 day composites
- 23 composite images/y
…
…
Remote Sensing Phenology –
MODIS NDVI 16 day composites and field plot comparison
0.4
August
y = 0.7475x + 0.0661
R² = 0.8482
NDVI
0.2
1:1
Linear (NDVI)
0.1
September
y = 0.5684x + 0.0925
R² = 0.6918
0.3
MODIS
0.3
0.2
NDVI
1:1
0.1
Linear (NDVI)
0
0
0
0.1
0.2
0.3
0
0.4
0.1
0.2
November
0.4
y = 0.6939x + 0.0807
R² = 0.7723
0.3
0.2
NDVI
1:1
Linear (NDVI)
0.1
0
0
0.3
0.4
Field Spectroradiometer
Field Spectroradiometer
MODIS
MODIS
0.4
0.1
0.2
0.3
0.4
Field Spectroradiometer
Remote sensing phenology
Spring green-up
From: http://phenology.cr.usgs.gov/
Remote sensing phenology: Fourier method
Remote sensing phenology: Fourier method
Remote sensing phenology
Year of fire
0.3
NDVI
Fire
0.2
0.1
0.0
0
64
128
192
Julian Date
256
320
Remote sensing phenology
Year of fire
0.3
NDVI
Fire
Fall green-up
0.2
0.1
0.0
0
64
128
192
Julian Date
256
320
Remote sensing phenology
Year after fire
0.3
NDVI
Spring green-up
0.2
0.1
0.0
0
64
128
192
Julian Date
256
320
Remote sensing phenology: Fourier method
Year of fire
2nd term: fall green-up
0.50
1st Term
2nd Term
Magnitude
0.25
0.00
-0.25
-0.50
0
64
128
192
Julian Date
256
320
Remote sensing phenology: Fourier method
Year after fire
1st term: spring green-up
0.50
1st Term
2nd Term
Magnitude
0.25
0.00
-0.25
-0.50
0
64
128
192
Julian Date
256
320
What will be the impact of a longer fire season?
Will more early season fires = longer disturbance windows?
NDVI
Do post-fire seeding treatments = shorter disturbance windows?
Period of enhanced erosion
Date (YY)
What will be the impact of a longer fire season?
Will more early season fires = longer disturbance windows?
NDVI
Do post-fire seeding treatments = shorter disturbance windows?
Period of enhanced erosion
Date (YY)
Does the length of the disturbance window vary with time of year that fires burn?
- Fall (MODIS, 2000… )
150
Days Bare (Fire - Fall Green-up)
R2 = 0.47
100
50
0
150
175
200
Fire Date
225
250
Does the length of the disturbance window vary with time of year that fires burn?
- Spring (MODIS, 2000… )
450
Days Bare (Fire - Spring Green-up)
R2 = 0.28
400
350
300
250
200
150
175
200
Fire Date
225
250
AVHRR (1990…)
Precipitation
• Marginal increase in the strength of the disturbance
window vs. fire date relationship with incorporation of
precipitation received during the first year after fire as
an additional predictor
Post-fire seeding treatments
Post-fire seeding treatments
Summary
• Disturbance windows (post-fire green-up as proxy for soil
stabilization) appear to vary with fire date
• Early relative to late season fires appear to result in longer
periods of bare soil
• Prioritize rehabilitation and soil stabilization efforts
• No substantial effects of seeding treatments on short term, postfire vegetation greenness dynamics
http://birrell.org
Acknowledgements
• Research supported by a USGS Mendenhall Fellowship
• USGS-WGSC and USGS-FRESC
Longer term (~10-20 y) post-fire vegetation
1.0
Burned and Seeded
Burned, Not Seeded
Not Burned
Fractional Cover
0.8
0.6
0.4
0.2
0.0
Perennial
Annual+Perennial
Vegetation Components
BRTE