Changes in pine volumes across the U.S. South following updated NSVB equations

by David Rossi and Ray Sheffield

In October, the U.S. Forest Service updated the FIA database to reflect their updated methodology for estimating merchantable forest inventory volume, biomass volume, and carbon storage (see Westfall et al., 2023). These new datasets provide a consistent methodology for estimating inventory volumes across different regions of the U.S., in contrast to previous methods which relied on alternative techniques in different regions. This update not only changes future inventory, growth, and removal estimates across the U.S. South, but it also changes historical trends in these measurements.

This article is the first in a series of comments highlighting changes in the SRTS-ready FIA data across the U.S. South following this change in the USFS methodology. The focus of this first post is to highlight basin-level changes in pine volume across the old version of the SRTS data (v37a) and the new version (v2023b) within the 8 states where only the methodology for estimating inventory volume, biomass, and carbon has changed (and where no new survey data was compiled).[1]

All states in the U.S. South were affected by this update, but the extent of the impact depends on forest types, species groups, age classes, and survey units across the U.S. South. The latest version of the SRTS data (v2023b) includes 5 states with updated survey data (North Carolina, South Carolina, East Oklahoma, Virginia, and Kentucky), and so estimated changes in these states across versions 37a and 2023b may reflect both changes in methodology and the addition of more recent survey data. There are 8 states with no new survey data but only changes to the volume estimation methodology (Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, Tennessee, and East Texas).

 Tables 1-8 below provide estimates of changes in total growing stock pine inventory (“INV”), average growth per acre (“AVG. GPA”), and removals (“REM”) on private timberland across the v37a and v2023b data. Volume data in Tables 1-8 is expressed in MCF, except for average growth per acre which is expressed in cubic feet per acre. Since no new survey data was compiled and the new NSVB methodology does not impact acreage estimates, we do not observe any changes in timberland area across the v37a and v2023b data (“ACRES”).

The largest percentage changes in growing stock pine inventory volume occur in east Tennessee (+7.3%), the Plateau region of Tennessee (+5.6%), central Tennessee (+4.6%), the Ozark region of Arkansas (+4.5%), north-central Georgia (+3.4%), north Georgia (+2.5%), and northeast Florida (-3.2%).

The largest percentage changes in average per acre pine growth occur in the Mississippi Delta basin (+6.5%), west-central Alabama (+4.4%), central Mississippi (+4.1%), north-central Georgia (+4.1%), north-southwest Alabama (+4.0%), southwest Mississippi (+3.9%), and north Mississippi (+3.7%).

Excluding the Mississippi River Delta basins and south Florida where there is very little industrial pine harvesting activity, the largest percentage changes in removals occur in the plateau region of Tennessee (-7.7%), northeast Florida (-6.8%), northwest Florida (-4.4%), central Tennessee (-3.8%), west Tennessee (-3.4%), southeast Texas (-3.4%), southeast Georgia (-3.3%), north Alabama (-3.2%), and south-southwest Alabama (-3.1%). These removal estimates in Tables 1-8 below exclude removals from timberland conversion.

            For estimates of changes in the v2023b data for different states, species, age classes, or forest types, please contact David Rossi (drossi2@ncsu.edu).

Table 1: Alabama (pine)

Table 2: Arkansas (pine)

Table 3: Florida (pine)

Table 4: Georgia (pine)

Table 5: Louisiana (pine)

Table 6: Mississippi (pine)

Table 7: Tennessee (pine)

Table 8: East Texas (pine)

References

Westfall, J., J. Coulston, A. Gray, J. Shaw, P. Radtke, D. Walker, A. Weiskittel, D. MacFarlane, D. Affleck, D. Zhao, H. Temesgen, K. Poudel, J. Frank, S. Prisley, Y. Wang, A. Sanchez Meador, D. Auty, G. Domke. 2023. A national-scale tree volume, biomass, and carbon modeling system for the United States. U.S. Department of Agriculture, Forest Service. Northern Research Station. General Technical Report WO-GTR-104. Washington, D.C. https://doi.org/10.2737/WO-GTR-104. Last accessed: 27 Nov. 2023.

End Notes

[1] Note that a USFS summary of state-level changes across different species groups and volume types can be found at: https://charcoal2.cnre.vt.edu/nsvb_factsheets/index.html.