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Uncertainty in Forest Carbon and Nutrient Budgets
Ruth D. Yanai
State University of New YorkCollege of Environmental Science and Forestry
Syracuse NY 13210, USA
Quantifying uncertainty in ecosystem budgetsPrecipitation (evaluating monitoring intensity)Streamflow (filling gaps with minimal uncertainty)Forest biomass (identifying the greatest sources of uncertainty)Soil stores (detectable differences)
QUANTIFYING UNCERTAINTY IN ECOSYSTEM STUDIES
UNCERTAINTY
Natural Variability
Spatial Variability
Temporal Variability
Knowledge Uncertainty
Measurement Error
Model Error
Types of uncertainty commonly encountered in ecosystem studies
Adapted from Harmon et al. (2007)
Bormann et al. (1977) Science
How can we assign confidence in ecosystem nutrient fluxes?
Bormann et al. (1977) Science
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
Net N gas exchange = sinks – sources = - precipitation N input+ hydrologic export+ N accretion in living biomass+ N accretion in the forest floor ± gain or loss in soil N stores- weathering N input
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Measurement Uncertainty Sampling UncertaintySpatial and Temporal Variability
Model Uncertainty
Error within models Error between models
Volume = f(elevation, aspect): 3.4 mm
Undercatch: 3.5%Chemical analysis: 0-3%
Model selection: <1%
Across catchments:
3%
Across years:
14%
We tested the effect of sampling intensity by sequentially omitting individual precipitation gauges.
Estimates of annual precipitation volume varied little until five or more of the eleven precipitation gauges were ignored.
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Yanai, Levine, Green, and Campbell (2012) Journal of Forestry
Don Buso HBES
Gaps in the discharge record are filled by comparison to other streams at the site, using linear regression.
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Cross-validation: Create fake gaps and compare observed and predicted discharge
Gaps of 1-3 days: <0.5%Gaps of 1-2 weeks: ~1%
2-3 months: 7-8%Yanai et al. (2014) Hydrological Processes
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass + N accretion in the forest floor± gain or loss in soil N stores
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass + N accretion in the forest floor± gain or loss in soil N stores
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Tree Inventory
log(Height) = a + b*log(Diameter) ± errorlog (Mass) = a + b*log(1/2 r2 *Height) ± error
Nutrient content = Mass * (Concentration ± error)Sum all trees and all tissue types
Allometric Equations
and Nutrient Concentrations
Monte Carlo
Simulation
Yanai, Battles, Richardson, Rastetter, Wood, and Blodgett (2010) Ecosystems
Monte Carlo simulations use random sampling of the distribution of the inputs to a calculation. After many iterations, the distribution of the output is analyzed.
Repeated Calculations of N in Biomass
Hubbard Brook Watershed 6
611 ± 54 kg N/ha
Nitrogen Content of Biomasswith Uncertainty
***IMPORTANT***
Random selection of parameter values applies across all the trees and all the time periods in each iteration.
The uncertainty between two measurements can be less than in a single measurement!
100 Simultaneous Calculations of N in Biomass in 1997 and 2002
100 Simultaneous Calculations of N in Biomass in 1997 and 2002
Accumulation Rate of N in Biomass
Distribution of Estimates
18 ± 5 kg N/ha over 5 yr
C1 C2 C3 C4 C5 C6 HB-Mid JB-Mid C7 C8 C9 HB- Old JB-Old
Young Mid-Age Old
Biomass of thirteen standsof different ages
C1 C2 C3 C4 C5 C6 HB-Mid JB-Mid C7 C8 C9 HB- Old JB-Old
3% 7% 3%
4% 4% 3% 3% 3%
3% 2% 4% 4% 5%
Coefficient of variation (standard deviation / mean)of error in allometric equations
Young Mid-Age Old
C1 C2 C3 C4 C5 C6 HB-Mid JB-Mid C7 C8 C9 HB- Old JB-Old
Young Mid-Age Old
3% 7% 3%
4% 4% 3% 3% 3%
3% 2% 4% 4% 5%
CV across plots within stands (spatial variation)Is greater than the uncertainty in the equatsions
6% 15% 11%
12% 12% 18% 13% 14%
16% 10% 19% 3% 11%
Yanai, Levine, Green, and Campbell (2012) Journal of Forestry
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass (± 1)+ N accretion in the forest floor± gain or loss in soil N stores
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass (± 1)+ N accretion in the forest floor± gain or loss in soil N stores
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Oi
Oe
Oa
E
Bh
Bs
ForestFloor
MineralSoil
Nitrogen in the Forest FloorHubbard Brook Experimental Forest
Nitrogen in the Forest FloorHubbard Brook Experimental Forest
The change is insignificant (P = 0.84).The uncertainty in the slope is ± 22 kg/ha/yr.
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass (± 1)+ N accretion in the forest floor (± 22)± gain or loss in soil N stores
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Studies of soil change over time often fail to detect a difference.We should always report how large a difference is detectable.
Yanai et al. (2003) SSSAJ
Power analysis can be used to determine the difference detectable with known confidence
Yanai et al. (2003) SSSAJ
Sampling the same experimental units over time permits detection of smaller changes
Yanai et al. (2003) SSSAJ
In this analysis of forest floor studies, few could detect small changes
Yanai et al. (2003) SSSAJ
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass (± 1)+ N accretion in the forest floor (± 22)± gain or loss in soil N stores
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Nitrogen Pools (kg/ha)Hubbard Brook Experimental Forest
Forest Floor
Live Vegetation
Coarse Woody Debris
Mineral Soil10 cm-C
Dead Vegetation
Mineral Soil0-10 cm
Yanai et al. (2013) ES&T
Quantitative Soil Pits0.5 m2 frame
Excavate Forest Floor by horizonMineral Soil by depth increment
Sieve and weigh in the fieldSubsample for laboratory analysis
In some studies, we excavate in the C horizon!
We can’t detect a difference of 730 kg N/ha in the mineral soil.
From 1983 to 1998, 15 years post-harvest, there was an insignificant decline of 54 ± 53 kg N ha-1 y-1
Huntington et al. (1988)
Yanai et al. (2013) ES&T
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass (± 1)+ N accretion in the forest floor (± 22)± gain or loss in soil N stores (± 53)
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± ?? kg/ha/yr
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass (± 1)+ N accretion in the forest floor (± 22)± gain or loss in soil N stores (± 53)
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± 57 kg/ha/yr
Net N gas exchange = sinks – sources = - precipitation N input (± 1.3)+ hydrologic export (± 0.5)+ N accretion in living biomass (± 1)
The N budget for Hubbard Brook published in 1977 was “missing” 14.2 kg/ha/yr
14.2 ± 2.6 kg/ha/yr
Draw your budget boundaries to ask questions that can be answered with confidence!
The Value of Uncertainty Analysis
Quantify uncertainty in our resultsUncertainty in regressionMonte Carlo samplingDetectable differences
Identify ways to reduce uncertaintyDevote effort to the greatest unknowns
Improve efficiency of monitoring efforts
Be a part of QUEST!• Find more information at: www.quantifyinguncertainty.org
• Read papers, share sample code, stay updated with QUEST News• Email us at quantifyinguncertainty@gmail.com• Follow us on LinkedIn and Twitter: @QUEST_RCN
QUANTIFYING UNCERTAINTY IN ECOSYSTEM STUDIES
ReferencesYanai, R.D., N. Tokuchi, J.L. Campbell, M.B. Green, E. Matsuzaki, S.N. Laseter, C.L. Brown, A.S. Bailey, P. Lyons, C.R. Levine, D.C. Buso, G.E. Likens, J. Knoepp, K. Fukushima. 2014. Sources of uncertainty in estimating stream solute export from headwater catchments at three sites. Hydrological Processes. DOI: 10.1002/hyp.10265
Yanai, R.D., M.A. Vadeboncoeur, S.P. Hamburg, M.A. Arthur, M.A. Fuss, P.M.Groffman, T.G. Siccama, and C.T. Driscoll. 2013. From Missing Source to Missing Sink: Long-Term Changes in a Forest Nitrogen Budget. Environmental Science & Technology. 47(20):11440-11448.
Yanai, R.D., C.R. Levine, M.B. Green, and J.L. Campbell. 2012. Quantifying uncertainty in forest nutrient budgets, J. For. 110: 448-456
Yanai, R.D., J.J. Battles, A.D. Richardson, E.B. Rastetter, D.M. Wood, and C. Blodgett. 2010. Estimating uncertainty in ecosystem budget calculations. Ecosystems 13: 239-248
Wielopolski, L, R.D. Yanai, C.R. Levine, S. Mitra, and M.A Vadeboncoeur. 2010. Rapid, non-destructive carbon analysis of forest soils using neutron-induced gamma-ray spectroscopy. For. Ecol. Manag. 260: 1132-1137
Yanai, R.D., S.V. Stehman, M.A. Arthur, C.E. Prescott, A.J. Friedland, T.G. Siccama, and D. Binkley. 2003. Detecting change in forest floor carbon. Soil Sci. Soc. Am. J. 67:1583-1593
My web site: www.esf.edu/faculty/yanai (Download any papers)
Alternative spatial models for precipitation in the Hubbard Brook Valley
Alternative spatial models for precipitation in the Hubbard Brook Valley
0.36%
0.58%
0.24%
0.77%
0.83%
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