Download V2 - V1 = G – R

The Value of FIA Remeasurement
Data
Paul Van Deusen
NCASI
Sacramento, CA
March 9, 2011
Remeasured plots provide detailed change data
Issues related to using FIA GRM data
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Change formula: V2 - V1 = G – R – M
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This change accounting rule implies additivity
1) FIA GRM definitions won't add up to V2 - V1
2) Annual measurements lumped into evaluation
groups don't fit nicely into the accounting rule
Change Components: G – R - M
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FGROWCFGS = Net annual merchantable cubicfoot growth of a growing-stock tree on forest land
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FIA growth is negative if a tree dies before time 2
This means that G and M are confounded
FREMVCFGS includes trees that were removed for
products, for land conversion, and that die because
of human actions (part of mortality).
FMORTCFGS = Will include trees already counted
in G and R
FIA explains all of this in the user manual.
Should you use FIA GRM estimates
or compute your own?
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V2 – V1 = G – R – M won't add up, otherwise.
It is possible to compute estimates for G,R and
M according to other definitions
For example (to achieve additivity):
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Let G be based only on growth
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Let R include only trees removed for products
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Let M be mortality on land that was forested at
times 1 and 2
G/R Estimate for Maine
G/R estimate from FIA data suggests that Maine is not sustainable.
Adjusted G/R estimate suggests it is sustainable.
Other Federal
FIA GRM
18.3
Adjusted GRM 52.9
State/Local
Private
All
0.9
2.7
0.97
1.51
0.97
1.57
Done with GForest
What is time 1 or 2 with annual data?
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An evaluation group includes plots measured
over a range of years
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How can the accounting rule be applied?
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Create a change index analogous to V2/V1
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Ic = 1 + (G – R – M) / V
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All estimates can be based on the moving average
This is motivated by dividing both sides of the
accounting equation by V1, i.e.

V2/V1 = V1/V1 + (G – R – M)/V1
The Change Index for Maine
Computed for Biomass.
Based on a ratio relationship
Between sound volume and
Total Above Ground Biomass.
Computed with GCOLE.
See: Van Deusen and Roesch (2009), Forestry
Is the moving average adequate for
change estimation?
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The MA is adequate for the change index with 1
remeasurement
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What about when there are 3 or more
remeasurements?
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The MA is just the mean of an evaluation group.
Need to use a time series approach
A time series approach can also use annual
panels for trend estimates.
Maine: Mixed Estimator Trend
Sound volume (ft3/acre) by Inventory Year
Standard Errors
California: Mixed Estimator Trend
Sound volume (ft3/acre) by Inventory Year
Standard Errors
The need for GRM data in Florida
Foley Timber and Land Company
The concern is that fewer acres are being planted, but ....
More plantation acres are being harvested
Is Florida Facing Unsustainable
Plantation Harvesting?
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The concern is that plantation growth rates are
much greater than natural stand growth.
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Florida growth over removals ratio might be deteriorating
FIA has removed the Florida GRM data
Florida growth issue can't be addressed with FIA data
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How long should FIA wait before making GRM
data available for a state?
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This will soon be an issue in the West
Summary
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Standard FIA GRM estimates may not be what
users expect
Estimating change from GRM annual inventory
data is not as easy as with periodic data
The moving average is not adequate for
estimating trends
Should FIA put GRM data online as soon as
they are available for a state, or wait for several
years?
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In Florida, there might be an evolving problem that the
GRM data could detect.