what have we learned from forest tower flux data following disturbance? brian amiro, a. barr, j....
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What have we learned from forest tower flux data following
disturbance?Brian Amiro, A. Barr, J. Barr, T.A. Black, R. Bracho, M. Brown, J. Chen, K. Clark, K. Davis, A. Desai, S. Dore, V.
Engel, J. Fuentes, A. Goldstein, M. Goulden, T. Kolb, M. Lavigne, B. Law, H. Margolis, T. Martin, J.H. McCaughey, M. Montes-Helu, A. Noormets, J. Randerson, G. Starr, J. Xiao
Disturbances in North American Forests
(total area 7 million km2)• Fire: 40,000 km2/year• Harvest: 50,000 km2/year• Insects: larger• Storms/hurricanes: > 17,000 km2/year• Disease: ???
Disturbance Sequence Studies
• Our goal: Synthesize flux tower measurements of CO2 exchange for experiments designed to understand the effect of disturbance
• Chronosequence approach: forests of different ages
• Time series approach: follow a single site through a disturbance cycle
JGR 115: G00K02, doi:10.1029/2010JG001390, 2010
Acknowledgements: Large host of contributors and funders
Disturbance Chronosequenceswith Annual NEP measured by eddy covariance
Fire = 4Harvest = 7+Insects = 3Hurricane Wilma
Fire Sites: Boreal and Arizona
Forest Tent Caterpillar
Mountain Pine BeetleGypsy Moth
INSECTS
Harvesting: Practices highly variable. Clearcut, thinning…
Hurricane Wilma in October 2005; destroyed 30% of trees at a Florida mangrove site
Trajectory of hurricane Wilma during October 2005
Annual Carbon Flux from Eddy Covariance Towers
• Measure CO2 directly using fast-response anemometer and gas analyser
• Get 30-min mean fluxes• Calculate annual NEP (Net
Ecosystem Production)• Calculate GPP (Gross
Photosynthetic Production) and ER (Ecosystem Respiration) from tower data
• Networks: Ameriflux, Fluxnet-Canada (Canadian Carbon Program)
Age (years)
0 20 40 60 80 100
NE
P (
g C
m-2
y-1
)
-200
-100
100
200
300
0
Saskatchewan: PineManitoba: SpruceAlaska SpruceArizona: Pine
Annual NEP for fire chronosequences: boreal sites gaining carbon after 10 years
Fire: GPP and ER
GP
P (
g C
m-2
y-1 )
0
200
400
600
800
1000
Age (years)
0 20 40 60 80 100
ER
(g
C m
-2 y
-1)
0
200
400
600
800
1000
1200
SaskatchewanManitobaAlaskaArizona
ER relatively flat with age at boreal sites
Time to recovery from fire?Curve fit of NEP data from boreal fire sites
Boreal Forest Sites
Time Since Fire (years)
0 5 10 15 20 25 30
Cu
mu
lati
ve N
EP
(g
C m
-2)
-800
-400
400
800
1200
1600
0
2000
Typical range of mean carbon lost through combustion
Harvest Chronosequences: NEP
Age (years)
0 20 40 60 80 100
NE
P (
g C
m-2
y-1
)
-800
-600
-400
-200
200
400
600
800
0
1000
Saskatchewan: pineQuebec: spruceNew Brunwick: firVancouver Island: firOregon: pineFlorida: pineWisconsin: hardwoods
Harvest GPP and ER
Age (years)
0 20 40 60 80 100
ER
(g
C m
-2 y
-1)
0
500
1000
1500
2000
2500
GP
P (
g C
m-2
y-1
)
0
500
1000
1500
2000
2500
3000
SaskatchewanQuebecNew BrunswickVancouver IslandOregonFloridaWisconsin
Are there any relationships that apply with age following stand-replacing disturbance?
• Leaf area index (LAI) development?• What about GPP and ER relationships?
Ratio GPP/ER with age
Age (years)
0 20 40 60 80 100
GP
P/E
R
0.2
0.4
0.6
0.8
1.2
1.4
1.6
1.8
0.0
1.0
2.0
FireHarvest
Asymptote = 1.23
Ra = 0.55*GPP
Heterotrophic Respiration (normalized to mean for individual chronosequences)
assuming Ra = 0.55*GPP
Age (years)
0 20 40 60 80 100
Het
ero
tro
ph
ic R
esp
irat
ion
No
rmal
ized
0.0
0.5
1.0
1.5
2.0
2.5
FireHarvest
No statistically significant pattern with age
NEP Thinning: Harvest and Hurricane
Time since disturbance (years)
-2 -1 1 2 3 4 50
NE
P (
g C
m-2
y-1
)
-200
200
400
600
800
1000
1200
1400
0Florida HurricaneArizona ThinningNew Brunswick ThinningCalifornia Thinning
Insect sequences: NEP
Time since disturbance (years)
-2 -1 1 2 3 4 50
NE
P (
g C
m-2
y-1
)
-200
200
400
600
0
Mountain Pine BeetleForest Tent CaterpillarGypsy Moth
CFS web page
What have we observed?
• Forests become carbon sinks within 5 to 20 years following stand-replacing events
• GEP/ER ratio becomes relatively constant by 15 years
• Heterotrophic respiration variable with no strong age function
• Quick recovery in NEP following thinning• Insect effects variable: depends on nature of
infestation, but NEP becomes positive quickly
What should we do; where are the gaps?
• All sites were disturbed at some time, so when does the disturbance history become less important than inter-annual variability and other site factors?
• Do young sites respond to climate and stressors differently from more mature sites?
• Do we need more chronosequences? Where? For how long? Can we compare severity/management practices?
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