Evaluating revised biomass equations: are some forest types more equivalent than others?

Area of Science:

• Forestry and Ecological Sciences
• Biomass Estimation and Carbon Stock Assessment

Background:

• Two sets of biomass equations for temperate US forests exist: Jenkins et al. (2003) and Chojnacky et al. (2014), both meta-analytically derived.
• Both equation sets share methodological similarities, necessitating an evaluation of their comparative carbon stock estimates.
• Understanding differences is crucial for researchers and software utilizing these biomass equations.

Purpose of the Study:

• To compare carbon stock estimates derived from the Jenkins et al. (2003) and Chojnacky et al. (2014) biomass equations for US forests.
• To provide guidance on applying the newer Chojnacky et al. equations to US tree species.
• To assess the equivalence of carbon stock estimates between the two equation sets across different forest types and regions.

Main Methods:

• Meta-analysis of published equations to develop both Jenkins et al. (2003) and Chojnacky et al. (2014) biomass estimation models.
• Application of both equation sets to estimate total carbon stocks in live trees across the US.
• Equivalence testing of carbon stock estimates at national, regional, and forest type group levels.

Main Results:

• National-level total carbon stocks in live trees differed by less than one percent between the two equation sets.
• Significant regional differences, sometimes exceeding 10-15%, were observed for specific regions and forest type groups.
• No consistent pattern emerged where one equation set systematically overestimated or underestimated carbon stocks compared to the other.

Conclusions:

• Biomass estimates are not equivalent for specific forest type groups, including southern pines, northern spruce-fir, and arid western forests.
• Estimates for the majority of forest type groups are generally equivalent at the presented scales.
• Aggregated summaries of equivalent forest type groups reduce the likelihood of substantial discrepancies between the Chojnacky and Jenkins equation sets.