Improving Individual Tree Biomass Equations for National-Scale Biomass Estimation

1. Improving Individual Tree Biomass Equations for National-Scale Biomass Estimation Bruce E. Borders, Professor Forest Biometrics 2011 FIA User Group Meeting Sacramento, CA March 9, 2011

2. Motivation • Great interest in forest biomass & carbon budgets throughout the world, including the U.S. • Clearly, the FIA network of timber inventory plots is the most logical inventory information to use for development of National Scale forest biomass & carbon budgets for the U.S.

3. Motivation • To develop biomass & carbon budgets that are scientifically defensible we must have reliable estimates of forest biomass (the basic building block for carbon estimation in forests) for all pertinent forest components for all timber types across the U.S. • Stemwood • Bark • Branches and foliage • Stump and coarse root

4. Literature Cited Below • Jenkins, J. C. and others. 2003. National scale biomass estimators for United States tree species. Forest Science 49(1): 12-35. • Pastor, J. and others. 1984. Biomass prediction using generalized allometric regression for some northeast tree species. For Ecol and Mgmt 7:265-274. • Heath, L.S. and others. 2009. Investigation into calculating tree biomass and carbon in the FIADB using a biomass expansion factor approach. In McWilliams, W. and others, editors Forest Inventory and Analysis (FIA) Symposium. Oct 21-23, 2008. Park City, UT. Proc RMRS-P-56CD. • Lambert, M.-C. and others. 2005. Canadian national tree aboveground biomass equations. Can J For Res 35: 1995-2018.

5. Current U.S. Forest Carbon Budgets • Based on FIA sample tree measurements and the associated forest area estimates • Biomass estimates developed for the various components based on the work of Jenkins and others (2003), which, according to Heath and others (2009) is: • “arguably the current standard for carbon estimates in the United States”

6. Current U.S. Forest Carbon Budgets • Jenkins and others (2003) • Clearly this work was the logical first step in the development of reliable national-scale biomass estimates • The scientists working on this project recognized the opportunity to use the FIA sample tree data in conjunction with individual tree biomass prediction functions

7. Current U.S. Forest Carbon Budgets • Jenkins and others (2003) • Consequently, they conducted an exhaustive search of the scientific literature and compiled a “comprehensive database of diameter-based biomass regressions for North American tree species” • These equations were used to implement a method proposed by Pastor and others (1984) in which equations are used to generate “pseudodata” and new functions were fitted to these data

8. Current U.S. Forest Carbon Budgets • Heath and others 2009 note that: • The official US forest carbon inventories (U.S. EPA 2008) relied on the work of Jenkins and others (2003) • FIADB3 dataset did not use the Jenkins and others equations for biomass estimation but, instead, used regional specific equations that are not based on FIA volume estimates • These authors go on to indicate that FIADB4 released in April, 2009 contains biomass estimates resulting from their component ratio method (CRM) that are ‘consistent with FIA volume estimates at tree-level’

9. Current U.S. Forest Carbon Budgets • It is generally agreed that nationally consistent estimates of forest biomass is a laudable goal • The works by both Jenkins and others (2003) and Heath and others (2009) develop estimates with this goal in mind

10. Current Biomass Equations • Various methods have been used by different FIA units around the country – often times, biomass component estimates are obtained for individual trees relative to FIA stem-wood volume estimates • This constraint can produce illogical estimates of total tree biomass estimates due to many factors – not the least of which is the fact that total tree biomass is often simply taken as the sum of the components that have each been related to stem volume – and hence there is no logical constraint on the components nor the total biomass estimates

11. Current Biomass Equations • Jenkins and others (2003) work was a good step in the right direction for trying to develop a consistent approach to estimating national-scale biomass/carbon budgets • However, they indicate that their effort did not produce the best possible biomass estimation equations because: • The available literature shows tremendous variability in biomass allocation from site to site and study to study – hence more information is required about differences in biomass and allocation of biomass among different tree species and sites

12. Current Biomass Equations • Jenkins’ and others (2003) go on to point out: • “Most published biomass equations were developed using trees sampled from isolated study sites or from very small regions. As a result, it is difficult to use existing biomass equations with forest inventory datasets at large spatial scales because the literature is site specific, often disorganized, and sometimes inconsistent. Existing compilations of equations are incomplete or ignore differences in tree component definitions.”

13. Current Biomass Equations • Lambert and others (2005) point out two problems with Jenkins’ and others methodology: • Use of the method of Pastor and others (1984) to generate pseudodata from available biomass equations results in high autocorrelation in the data and hence results in unbiased regression coefficient estimates but traditional estimates of variance for fitted regression coefficients are inappropriate and hence may lead to incorrect parameterization • Large potential for bias in the sample of papers selected at the national level – equations based on a single site with small sample size have the same weight as equations based on multiple sites with larger sample sizes

14. Current Biomass Equations • Lambert and others (2005) also report that in Canada they found artificial differences across provinces/territories due to different biomass estimation procedures used by the different provinces/territories – very similar to differences associated with various FIA units

15. Improving Biomass Equations • Lambert and others (2005) state: • “When forest inventory plot data are used for estimating biomass density, tree biomass equations that can be consistently applied on a national scale represent a basic tool for converting inventory plot data into biomass density.”

16. Improving Biomass Equations • Clearly, Jenkins and others (2003) agree with this premise because they tried to create such equations but were limited by available data. In fact, they state: • “Development of continental-scale regressions of known accuracy requires a continental-scale measurement campaign in which individuals of all species and sizes are measured, over the entire range of site conditions typical of each species. This would be a formidable task.”

17. Improving Biomass Equations • Lambert and others (2005) made use of individual tree biomass data from across Canada obtained in the 1980’s within the ENFOR (Energy from the FORest) program: • A national tree biomass data collection effort across Canada • Using these data consistent national scale biomass equations were developed • However, they noted there was a major problem in their resulting equations caused by the “absence of a standard sampling plan and of a standard tree harvesting protocol to collect the biomass.”

18. Improving Biomass Equations • Heath and others (2009) presented another methodology for developing consistent biomass equations for use at national scale in the U.S. • They also recognize and discuss the weaknesses that both Jenkins and others (2003) and Lambert and others (2005) noted and state that their own effort also suffers from these problems

19. Improving Biomass Equations • Heath and others (2009) state: • “A planned, coordinated, supported and funded national effort across FIA units and with other, interested scientific experts to develop tree level volume, biomass and carbon equations would increase the credibility and usefulness of the resulting biomass estimates, providing ‘high quality, consistent and reliable data … a several year effort … will be well worth the investment’”

20. Improving FIA Biomass Estimates • Clearly, there is agreement among scientists that the most appropriate methodology to estimate national scale forest biomass components should be based on: • Credible national scale timber inventory data (FIA) • Individual tree biomass prediction functions developed using an adequate sample of consistently measured individual trees for the most important timber types/species throughout the country

21. Improving Individual Tree Biomass Equations • These functions should be developed with flexibility and consistency of estimates in mind: • A common sampling/measurement protocol should be developed with input from experts from throughout the U.S. • These same experts have many ideas on how these functions should be structured to insure that they can be used for realistic/consistent component and total tree biomass estimates • Various university and USDA Forest Service units throughout the country should be identified to lead on the ground sampling/analysis work in each region – these units should be part of the discussions used to develop the sampling/measurement protocol and will be charged with implementing this protocol as established through such discussions • A single national center should be identified to organize/coordinate all protocol development, function development and ultimately a plan for implementation across FIA units

22. Improving Individual Tree Biomass Equations • The Central government in China recently funded just such an effort across China (personal communication – Dr. Dehai Zhao, UGA) • The program was coordinated from Beijing University • A common sampling protocol/harvesting strategy was developed and implemented regionally • Regional research centers were charged with implementing the protocol and collecting appropriate data • Each regional center also developed individual tree biomass functions separately from other regions • All data from across the country were compiled at Beijing University and national-scale functions were developed in this unit

23. Improving Individual Tree Biomass Equations • Yesterday, David Meriweather indicated that policy and management decisions on federal lands will be made with the ‘Best Science’ available • If we continue to obtain national-scale biomass/carbon budgets using the methodology used to date we will definitely not be using the ‘Best Science’ that is available • We know what the ‘Best Science’ is – we simply need the will to make it happen

24. Improving Individual Tree Biomass Equations • As my daddy always told me – “if you are going to do something – do it right” • We know what to do – do we have the will to do it? • Another old saying (dad or someone else) – “there’s no time like the present”