PROXY MODELS FOR Pseudotsuga menziesii (Mirb.) Franco STEM BIOMASS: PRESSLER METHOD

Abstract

Accurate assessment of tree biomass is necessary to estimate carbon stocks and understand the contribution of forest ecosystems in regulating greenhouse gas emissions. The objective of this study was to develop an allometric equation to predict stem biomass (Bf) for Pseudotsuga menziesii (Mirb.) Franco, in the Arteaga Coahuila region, in northeastern Mexico. The normal diameter (Dn), leader point height (Hp) and total height (Ht) were measured by using Criterion RD1000®. The stem volume (Sv) was obtained by applying the Pressler equation, and then it was transformed into biomass using the basic density of the wood. The data were adjusted through the potential model Ŷ = aXb in its logarithmic form, where Ŷ is Sb and X the Dn, assessing the assumptions of normality, homoscedasticity and no autocorrelation. A total of 110 sample trees of this species were sampled. The equation ln(Bf) = −2.8732 (± 0.238) + 2.4237 (± 0.066) × ln(Dn) fulfilled all the assumptions of lineal models (P- value > 0.05), ensuring that the stem biomass prediction is reliable. Normal diameter explained 98 % of the stem biomass of P. menziesii. The bias in the stem biomass prediction due to the logarithmic transformation must be corrected by multiplying it by a correction factor of 1.018. Indirect volume estimation by the Pressler method is an efficient, low-cost and non-destructive approach to generate an allometric model of stem biomass.