Allometric Equations for Estimating Compartment Biomass and Stem Volume in Mature Hybrid Poplars: General or Site-Specific?

Julien Fortier,Benoit Truax,Daniel Gagnon,France Lambert

doi:10.3390/f8090309

Abstract

We evaluated the extent to which general or site-specific allometric equations, using diameter at breast height (DBH) as a predictor, are more accurate for estimating stem volume, stem biomass, branch biomass, aboveground woody biomass, and coarse root biomass in 14 year-old plantations of Populus canadensis × Populus maximowiczii (clone DN × M-915508) located along an environmental gradient in southern Québec (eastern Canada). The effect of tree size and site on stem wood basic density, moisture content, and proportion of branch biomass was also evaluated. For stem volume, stem biomass, and aboveground biomass, site-specific and general models had comparable fit and accuracy, but lower Akaike’s Information Criterion (AICc) values were observed for the general models. For the branch and coarse root biomass, higher fit and accuracy and lower AICc values were observed for the site-specific models. Allometric trajectory changes (plastic allometry) across sites were mainly observed for coarse root biomass, branch biomass, and stem volume. On the low fertility site, allocation was increased to coarse roots and decreased to stem volume. Site-specific tradeoffs between tree architecture and stem wood density explained the relatively invariant allometry for the whole aboveground woody biomass across the plantation sites. On the high fertility sites, basic wood density was the lowest and declined as tree DBH increased. At all sites, stem wood moisture content and the proportion of branch biomass increased with DBH. Overall, this study showed that biomass allometry, tree architecture, and biomass quality are a function of both tree size and plantation environment in hybrid poplar. Allometric model selection (site-specific or general) should depend on the objective pursued (evaluation of yield, nutrient budget, carbon stocks).

Highlights

The afforestation of abandoned farmland with fast-growing species from the Salicaceae family provides tremendous opportunities to increase wood and biomass production, to sequester atmospheric carbon dioxide (CO2 ) in terrestrial ecosystems, and to accelerate forest ecosystem restoration [1,2,3]
The results from this study show that the plantation environment affects hybrid poplar The results from this study show that the plantation environment affects hybrid poplar aboveground tree architecture, while little plasticity aboveground tree architecture, while little plasticity waswas observed for the relationship between
This study has shown that the allometric relationships between diameter at breast height (DBH) and tree compartment biomass or stem volume were plastic, but not for all compartments

Summary

Introduction

The afforestation of abandoned farmland with fast-growing species from the Salicaceae family provides tremendous opportunities to increase wood and biomass production, to sequester atmospheric carbon dioxide (CO2 ) in terrestrial ecosystems, and to accelerate forest ecosystem restoration [1,2,3]. As nutrient-rich coarse roots and branch biomass are increasingly harvested for the production of bioenergy, off-site nutrient exportation is a growing concern because of its potential adverse impacts on soil fertility and long-term stand productivity [5,6,7]. To correctly evaluate the nutrient budget of hybrid poplar plantations and the impacts of whole-tree harvest vs stem harvest on carbon and nutrient cycling, and on the provision of several key ecosystem services in planted forests (C and nutrient storage, biomass and wood production, microclimate and habitat creation), an accurate knowledge of plantation structure and biomass distribution in different tree compartments is required. The estimation of stem volume and compartment biomass at the plantation-scale often requires that trees of various sizes be felled, dissected into components, and weighed or measured [8]. The biomass and volume data obtained from these destructive sampling procedures are used to develop allometric equations between a predictor variable that is measurable in the field, usually diameter at breast height (DBH), and response variables, such as stem volume or the biomass of a given tree compartment

Methods

Results

Conclusion