Variation in trunk taper of buttressed trees within and among five lowland tropical forests

• Published in: Biotropica 2021-09, Vol.53 (5), p.1442-1453
• Main Authors: Cushman, K. C., Bunyavejchewin, Sarayudh, Cárdenas, Dairon, Condit, Richard, Davies, Stuart J., Duque, Álvaro, Hubbell, Stephen P., Kiratiprayoon, Somboon, Lum, Shawn K. Y., Muller‐Landau, Helene C.
• Format: Article
• Language: English
• Subjects: aboveground biomass; Bias; Biomass; buttressed trees; Buttresses; Carbon; Density; Diameters; Error analysis; Estimates; Forest biomass; forest dynamics; forest plots; Forests; Haliporoides diomedeae; Measurement; measurement error; photogrammetry; Tapering; Trees; Tropical climate; tropical forest; Tropical forests; trunk taper; Variation; Wood
• ISSN: 0006-3606; 1744-7429
• DOI: 10.1111/btp.12994

Accurately projecting global carbon dynamics requires understanding controls over temporal and spatial tropical forest biomass variation. Changes in tropical forest aboveground biomass per area are most commonly estimated using repeat forest plot censuses, but errors in these estimates can be relatively large, limiting our ability to detect real changes in forest carbon. One source of error is nonstandard heights of diameter measurement, which are common in tropical forests because buttressed trees are usually measured above buttresses. Nonstandard and temporally variable measurement heights affect biomass change estimates because tree trunks taper—higher measurements result in smaller diameters and, thus, smaller estimated biomass. Modeling trunk taper is a potential way to correct for biases associated with nonstandard and changing measurement heights. We measured trunk taper for 260 buttressed trees in five lowland tropical forests to assess variation in taper within and among sites. Trunks taper more slowly in trees with larger diameters above buttress, taller buttresses, and higher wood density; these variables together explain 29% of taper variation. We also used plot data to quantify the distribution of measurement heights—and potential for bias in biomass estimates. We found significant variation in measurement heights among plots, and over time within plots. At the site level, our general taper model (taper predicted from diameter above buttress, buttress height, and wood density) produced site‐level biomass estimates within 3.4%, on average, of estimates from measured taper. We recommend using this model to reduce bias from nonstandard measurement heights in studies of tropical forest biomass variation. in Spanish is available with online material. Resumen Para entender la dinámica del carbono en los bosques tropicales se requiere conocer los factores que determinan la vairación espacial y temporal de la biomasa aérea. En los bosques tropicales, los cambios de la biomasa aérea por unidad de área se estiman principalmente usando medidas repetidas sobre parcelas permanentes. Sin embargo, errores debido a sesgos en los estimados pueden ser realtivamente altos, lo cual limita nuestra capacidad de detectar los cambios reales en las reservas de carbono almacenadas en los bosques. Una causa común de sesgo es la medición del diámetro a diferentes alturas. La imposibilidad de estandarizar la altura de medición de los diámetros a 1,3 m en los bosques tropi