The Value of FIA Remeasurement Data

Paul Van DeusenNCASI

Sacramento, CAMarch 9, 2011

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

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

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.

Should you use FIA GRM estimates or 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

G/R Estimate for Maine

Other Federal State/Local Private All

FIA GRM 18.3 0.9 0.97 0.97Adjusted GRM 52.9 2.7 1.51 1.57

G/R estimate from FIA data suggests that Maine is not sustainable.

Adjusted G/R estimate suggests it is sustainable.

Done with GForest

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

The Change Index for MaineComputed for Biomass.

Based on a ratio relationshipBetween sound volume andTotal Above Ground Biomass.

Computed with GCOLE.

See: Van Deusen and Roesch (2009), Forestry

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.

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?

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 dataFlorida 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

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.