Abstract
Aim of study: Cross-sectional area is one of the most important forest inventory variable since it is highly correlated with growth and yield at both tree and stand levels. In this research, we evaluated the bias, precision and accuracy of three measurements such as cross-sectional area: the girth, the arithmetic mean diameter, and the geometric mean diameter normally used to estimate the cross-sectional area in practical forestry.Area of study: Measurements were taken in a poplar plantation (Populus x euramericana (Dode) Guinier cv. Luisa Avanzo) located in Huesca, Spain.Material and Methods: A total of 5,408 cross-sectional areas from 48 poplar trees were measured with and image based software. To test the differences between real and estimated cross-sectional area based on the three measurements of study, a multilevel mixed-effect model was used.Main Results: All three measurements overestimated the cross-sectional area by (0.47%-2.37%) and were found to be biased. Estimations based on arithmetic or geometric mean diameter of the maximum and minimum axes were more accurate than those using tree girth.Research highlights: There was a strong correlation between estimation errors and departures from a circumference in the cross section i.e. estimation errors were larger in elliptical cross-sections than in those closer to a circumference. In order to avoid overestimation of growth and yield derived from cross-sectional area estimates, we recommend using the geometric mean diameter trying to measure the largest and the smallest diameters of the section, especially on trees that are clearly elliptical.Keywords: diameter; circumference; cross-sectional area; poplar plantations.
Highlights
Accurate tree volume and biomass estimations are central in forestry, since their information is used for foresters when deciding amongst forest management options or when conducting research
Estimations based on arithmetic or geometric mean diameter of the maximum and minimum axes were more accurate than those using tree girth
Research highlights: There was a strong correlation between estimation errors and departures from a circumference in the cross section i.e. estimation errors were larger in elliptical cross-sections than in those closer to a circumference
Summary
Accurate tree volume and biomass estimations are central in forestry, since their information is used for foresters when deciding amongst forest management options or when conducting research. Both volume and biomass are well correlated and estimated based on basal area measures, which is defined as the crosssectional area at breast height (Mackie & Matthews, 2006). Cross-sectional area can be measured directly using a planimeter, though this is rarely done in practice. Instead, it is usually estimated upon diameter measures assuming a circular section. Instead of the arithmetic average has been found to produce the lowest bias (Matérn, 1990; Chacko, 1961)
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