cascading thresholds
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Cascading Thresholds
• Subsistence-related changes• Warming to fire to permafrost loss to wetland drying to subsistence change
• Warming to fire to altered moose/caribou habitat/access to subsistence change
• Cultural assimilation to declining subsistence
• Declining subsistence to decreased well-being to migration to cities
• Economics-related changes• Global oil shortage to rising village oil prices to migration
• Warming to low river level to no barge deliveries to rising fuel costs to migration
• Warming to drought to spruce budworm to dry firewood to biofuels to jobs
• Warming to permafrost thaw to infrastructure costs to school/airport loss
• Rising fire suppression costs to fire co-management to resource manag. plan
• Rising fuel costs to smaller hunting radius to altered animal distrib to altered veg
1. Current experimental design/data collection and ties to future experimental design
2. Future experimental design
3. New experiments
Fate of datasets – three main decisions
1. Whether to maintain a data collection
2. Whether to maintain all replicates
3. Whether to maintain sampling frequency
Potential considerations and criteria for deciding future data collection efforts (i.e., future of present data collection efforts).
I. Considerations to maintain a data collection:• Data supportive of other research• Data are central to broader BNZ research objectives• Detected or potential to detect important change in ecosystem/community
structure• Cost and labor relative to importance/value of data
II. Considerations to maintain replicates• Detected or potential to detect important divergent patterns over time• Do existing data sufficiently quantify spatial variation to the point where
replication can be pared-down?
III. Considerations to maintain sampling frequency• Shorter term dynamics are relevant ecologically and to BNZ goals
Integration and Synthesis – New Experiment
How will potential changes in ecosystem structure alter material fluxes across the landscape
Potential Changes:• Permafrost thaw & thermokarst• Change in alder abundance• Others…
Response variables:• Carbon and nitrogen fluxes• Energy exchange• Successional trajectories• Others…
Experimental design (or start of design):• Watershed approach to monitor hydrologic and gaseous fluxes• Alder removal• Soil warming• Other manipulations???
Experimental Approaches to Threshold Change
Problem: Threshold changes usually require strong drivers that may be difficult to replicate with experiments
Examples:
Ecosystem warming experiments that minimally warm the soil
Fire experiments that burn at moderate or low severity
"Ap
par
ent"
Tem
per
atu
re S
ensi
tivi
ty
Environmental C
onstraints
sorbed
desorbed
aggregated
unaggregated
anaerobic
a
erobic
water stre
ss
adequate water
frozen
unfrozen
"Intrinsic" Temperature Sensitivity
simple complex
substrates substrates
high low
temperature temperature
Davidson and Janssens. 2006. Nature 440:165-173
Davidson and Janssenns, 2006 and Janssens. 2006. Nature 440:165-173
Soil Organic Matter
The roles of substrate and environment
Sensitivities to Climate, succession,regime shifts
Soil Organic Matter
How are SOM stocks and turnover changing?
•Causal linksSubstrate controlsEnvironmental controls
•Interactive effectsSubstrate X Environment
•Feedbacks to Ecosystem
Goal is to establish:
• Synthesis activities: • site scale models for lter 1, lter 2, lter wet, cpcrw • Litterbag and substrate models
• New long-term experiments• Litterbag and incubation, anchored in 5 yr C stock
harvests: • Locations via substrate X enviroment
• Historic evaluation of archives, data for substrate,environment
Soil Organic Matter
Fairbanks summer temperature 3-yr. Index vs. Yukon River ws ring-width
(all trees; n = 146; 2001:1906)
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
20
04
20
00
19
96
19
92
19
88
19
84
19
80
19
76
19
72
19
68
19
64
19
60
19
56
19
52
19
48
19
44
19
40
19
36
19
32
19
28
19
24
19
20
19
16
19
12
19
08
year
mean
rin
g w
idth
(m
m)
12.0
14.0
16.0
18.0
May,
Ju
l-1
&-2
tem
pera
ture
(C
)
All Yukon Flats 146 Temperature Index
Correlation of monthly precipitation at Fairbanks with residual of temperature prediction of growth
-0.30
-0.20
-0.10
0.00
0.10
0.20
0.30
0.40
month
corr
ela
tio
n (
Pe
ars
on
)
A.A. 2nd half 2nd halfwinter snowwinter snow
A.A. A.A.
year of ringyear of ringformationformation
1 year prior to1 year prior to ring formationring formation
2 years prior to2 years prior to ring formationring formation
Juday and Alix - IPEV/UAFJuday and Alix - IPEV/UAF
sig.@sig.@95%95%
sig.@sig.@95%95%
C.C. Nov Dec Nov Dec snow (neg)snow (neg)
B.B. Jul Aug Jul Aug rainrain
B.B. Aug Aug rainrain
= selected for= selected formodel (positive)model (positive)
= selected for= selected formodel (negative)model (negative)
rr22 = .46 = .46
Precipitation effect on temperature prediction of growth
(Yukon Flats w. spruce; 2001-1909; no 1991, 1963, 1928, 1926)
R2 = 0.35
R2 = 0.55
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
4.0
5.0
-3.0 -2.0 -1.0 0.0 1.0 2.0 3.0
Precipitation Index (stdev)
Re
sid
uals
of
Tem
p p
red
icti
on
(std
ev)
Juday and Alix - IPEV/UAFJuday and Alix - IPEV/UAF
Compensatory effectCompensatory effectof adding moistureof adding moisture
Deleterious effectDeleterious effectof withdrawing moistureof withdrawing moisture
Above medianAbove mediantemperaturetemperature
Below medianBelow mediantemperaturetemperature
smoothed Climate index vs. actual growth growth
(Yukon Flats w. spruce; all trees; n = 146; 2001-1909)
0.7
0.9
1.1
1.3
1.5
-4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0
Precip and Temp Index (stdev)
5-y
r. M
ean
Sam
ple
rin
g w
idth
(std
ev)
cool/moistcool/moisthot/dryhot/dry
rr22 = .77 = .77
LowerLowerthreshold? threshold?
UpperUpperthreshold? threshold?
Range ofRange ofsensitivity? sensitivity?
Future directions for vegetation
dynamics: Scaling in time and space
From McGuire, Chapin, Walsh, and Wirth. 2006. Integrated regional changes in arctic climate feedbacks: Implications for the global climate system. Annual Review of Environment and Resources 31:61-91.
PhysiologyClimate warming
Structure
Land Use
composition, vegetation shifts
Disturbance
CO2, SH
Permafrostwarming, thawing
Physical feedbacks
Biotic controlMediatingprocesses
Snowcover
1, 2, 3, 4
5, 6, 7
8, 9
10, 11
12, 13
A
B
C
14
15
16
enzymes, stomates
fire, insects
logging, drainage,reindeer herding
D
E
I
II
IV
III V
fast (seconds to months)intermediate (months to years)slow (years to decades)
Response time
Mechanisms:: albedoGH: ground heat fluxSH: sensible heat fluxCO2, CH4: atmospheric concentration
Physiological feedbacks:(1) higher decomposition CO2(2) reduced transpiration SH (3) drought stress: CO2(4) PF melting: CH4(5) longer production period: CO2(6) NPP response to N min: CO2(7) NPP response to T: CO2
Structural feedbacks:(8) shrub expansion: (9) treeline advance: , CO2 (10) forest degradation but CO2, SH (11) light to dark taiga: but CO2, SH(12) more deciduous forest: , SH(13) fire / treeline retreat:
Physical feedbacks:(14) increased, then reduced heat
sink GH,SH(15) watershed drainage SH(16) earlier snowmelt
Climatewarming
Soil climate
Physical feedbacks Biotic control
Snow cover PhysiologyPhenology, Growth rates, Mineralization
StructureComposition,Species shifts
Soil temperatureSoil moistureWater table position
Fig 1. Schematic of potential physical, physiological, and structural feedbacks to peatland C fluxes investigated in the proposed research. Response times of feedbacks vary from fast (seconds to months; i.e., NPP responses to temperature), to intermediate (months to yrs; i.e., NPP responses to longer growing seasons) and slow (yrs to decades; i.e., NPP responses to woody expansion).
Snowpack thicknessDuration of snowpack
Climatewarming
Soil climate
Physical feedbacks Biotic control
Snow cover PhysiologyPhenology, Growth rates, Mineralization
StructureComposition,Species shifts
Soil temperatureSoil moistureWater table position
Fig 1. Schematic of potential physical, physiological, and structural feedbacks to peatland C fluxes investigated in the proposed research. Response times of feedbacks vary from fast (seconds to months; i.e., NPP responses to temperature), to intermediate (months to yrs; i.e., NPP responses to longer growing seasons) and slow (yrs to decades; i.e., NPP responses to woody expansion).
Snowpack thicknessDuration of snowpack
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