An evaluation of the conical approximation as a generic model for estimating stem volume, biomass and nutrient content in young Eucalyptus plantations |
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| Authors: | S J Rance D S Mendham D M Cameron T S Grove |
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| Institution: | (1) CSIRO Ecosystem Sciences, Private Bag 5, Wembley, WA, 6913, Australia;(2) CSIRO Ecosystem Sciences and CRC Forestry, Private Bag 12, Hobart, TAS, 7001, Australia;(3) Sustainable Forestry Program, School of Environmental Science and Management, Southern Cross University, P.O. Box 157, Lismore, NSW, 2480, Australia; |
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| Abstract: | Accurately and non-destructively quantifying the volume, mass or nutrient content of tree components is fundamental for assessing
the impact of site, treatment, and climate on biomass, carbon sequestration, and nutrient uptake of a growing plantation.
Typically, this has involved the application of allometric equations utilising diameter and height, but for accurate results,
these equations are often specific to species, site, and silvicultural treatment. In this study, we assessed the value of
incorporating a third piece of information: the height of diameter measurement. We derived a more general volume equation,
based on the conical approximation, using a diameter projected to the base of the tree. Common equations were developed which
allowed an accurate estimate of stem volume, dry weight and nutrient content across two key plantation grown eucalypt species,
Eucalyptus grandis W. Hill ex Maiden and Eucalyptus globulus (Labill.). The conical model was developed with plantation-grown E. grandis trees ranging from 0.28 to 15.85 m in height (1.05 g to 80.3 kg stem wood dry weight), and E. globulus trees ranging from 0.10 to 34.4 m in height (stem wood dry weight from 0.48 g to 652 kg), grown under a range of contrasting
cultural treatments, including spacing (E.
grandis), site (E.
globulus) and fertilization (nitrogen and phosphorus) for both species. With log transformed data the conical function (Vcon) was closely related to stem sectional volume over bark and stem weight (R2 = 0.996 and 0.990, respectively) for both E.
grandis and E.
globulus, and the same regressions can be applied to both species. Back transformed data compared with the original data yielded modelling
efficiencies of 0.99 and 0.97, respectively. Relationships between Vcon and bark dry weight differed for the two species, reflecting differing bark characteristics. Young trees with juvenile foliage
had a different form of relationship to older trees with intermediate or adult foliage, the change of slope corresponding
to heights about 1.5 m for E. grandis and age 1 year for E. globulus. The Vcon model proved to be robust, and unlike conventional models, does not need additional parameters for estimating biomass under
different cultural treatments. More than 99% of the statistical variance of the logarithm of biomass was accounted for in
the model. Vcon captures most of the change in stem taper associated with cultural treatments and some of the change in stem form that occurs
after the crown base has lifted appreciably. Fertilization increased N and P concentrations in stem wood and bark, and regressions
to estimate N and P contents (the products of biomass and concentration) were dependent on treatment. For instance, there
was a large growth response to N fertilization in E. globulus corresponding with a change (P < 0.05) in the intercept of the regression to estimate N content. |
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