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The Value of FIA Remeasurement Data

Paul Van Deusen NCASI Sacramento, CA March 9, 2011. The Value of FIA Remeasurement Data. Remeasured plots provide detailed change data. Issues related to using FIA GRM data. Change formula: V2 - V1 = G – R – M This change accounting rule implies additivity

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The Value of FIA Remeasurement Data

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  1. Paul Van Deusen NCASI Sacramento, CA March 9, 2011 The Value of FIA Remeasurement Data

  2. Remeasured plots provide detailed change data

  3. Issues related to using FIA GRM data • Change formula: V2 - V1 = G – R – M • 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

  4. Change Components: G – R - M • FGROWCFGS = Net annual merchantable cubic-foot growth of a growing-stock tree on forest land • 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.

  5. Should you use FIA GRM estimatesor compute your own? • 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): • Let G be based only on growth • Let R include only trees removed for products • Let M be mortality on land that was forested at times 1 and 2

  6. 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. Done with GForest

  7. What is time 1 or 2 with annual data? • An evaluation group includes plots measured over a range of years • How can the accounting rule be applied? • Create a change index analogous to V2/V1 • Ic = 1 + (G – R – M) / V • 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

  8. 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

  9. Is the moving average adequate for change estimation? • The MA is adequate for the change index with 1 remeasurement • The MA is just the mean of an evaluation group. • What about when there are 3 or more remeasurements? • Need to use a time series approach • A time series approach can also use annual panels for trend estimates.

  10. Maine: Mixed Estimator Trend Sound volume (ft3/acre) by Inventory Year Standard Errors

  11. California: Mixed Estimator Trend Sound volume (ft3/acre) by Inventory Year Standard Errors

  12. The need for GRM data in Florida Foley Timber and Land Company

  13. The concern is that fewer acres are being planted, but ....

  14. More plantation acres are being harvested

  15. Is Florida Facing Unsustainable Plantation Harvesting? • The concern is that plantation growth rates are much greater than natural stand growth. • 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 • How long should FIA wait before making GRM data available for a state? • This will soon be an issue in the West

  16. Summary • 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? • In Florida, there might be an evolving problem that the GRM data could detect.

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