Biomass, stem basic density and expansion factor functions for five exotic conifers grown in Denmark

Abstract

Adequate allometric equations are needed for estimating carbon pools of fast growing tree species in relation to international reporting of CO₂ emissions and for assessing their possible contribution to increasing forest biomass resources. We developed models for predicting biomass, stem basic density and expansion factors of stem to above-ground biomass for five fast growing conifers. Data included destructive measurements of 236 trees from 14 sites, covering a wide range of growth conditions. To ensure model efficiency, models for predicting stem, crown and total above-ground biomass for the five species were estimated simultaneously using a linear, mixed effects model that allowed contemporaneous correlations between the different tree components. Models differed among species and included dbh and tree height. The models explained more than 98% of the variation in above-ground biomass and reflected differences in the allometry between tree species. Stem density differed among species but generally declined with increasing site index and dbh. The overall model for predicting stem basic density included dbh, H₁₀₀ and site index and explained 66% of the total variation. Expansion factors decreased from 1.8–2.0 in small trees (dbh < 10 cm) to 1.1–1.2 for large trees (dbh > 25 cm), but differed among species. The overall model explained 86% of the variation and included quadratic mean diameter and dbh.

Keywords:

• allometric model
• carbon
• mixed effect
• simultaneous estimation

Acknowledgements

We wish to acknowledge the effort of Christian Mørk Hansen, Rita Razauskaite, Allan Overgaard Nielsen and Bruno Bilde-Jørgensen for their tedious work with collecting field data and performing laboratory analyses.

Additional information

Funding

The project was supported by special grants from the Nature Agency, Ministry of Environment and Dalgas Innovation, Hedeselskabet and was conducted within the Nordic Energy Research supported ENERWOODS project. Finally, the project relied on goodwill as well as practical support from the Danish Nature Agency's regional units Nordsjælland, Vestjylland, Midtjylland and Vendsyssel as well as the forest districts Skjoldenæsholm and Løvenholm.