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Forest sampling combining fixed- and variable-radius sample plots

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Abstract:

We examine the statistical properties of a forest sampling strategy that combines methods of fixed- and variable-radius plot sampling. Circular fixed-radius plots are established at the same locations as variable-radius plots to take advantage of their known efficiencies for unbiasedly estimating stem density and basal area, respectively. The design eliminates the need for measuring stem diameters, except to check borderline trees on variable-radius plots. Separate controls on allowable error for stem density and basal area estimates are possible. An unbiased estimator of volume (Vol) is derived that uses an existing volume equation having the form Vol = a+ bd2h, where d is tree diameter at breast height, h is tree height, and a and b are model parameters. Calculation of volume requires only the measurement of heights for those trees tallied on the variable-radius plots. Properties of the estimator are demonstrated for a mixed-species hardwood forest in the southern Appalachian Mountains of North Carolina, USA.

Nous examinons les propriétés statistiques d’une stratégie d’échantillonnage forestier qui combine les méthodes d’échantillonnage par placettes à rayon fixe et à rayon variable. Les placettes circulaires à rayon fixe sont établies aux mêmes endroits que les placettes à rayon variable pour tirer profit de leur efficacité reconnue à produire des estimations non biaisées de la densité des tiges et de la surface terrière. Le dispositif élimine le besoin de mesurer le diamètre des arbres, sauf pour vérifier les arbres en bordure des placettes à rayon variable. Il est possible de contrôler l’erreur permise de l’estimation de la densité et celle de la surface terrière séparément. Un estimateur non baisé du volume (Vol) est dérivé à partir d’une équation de volume ayant la forme Vol = a + bd2h; cet estimateur exige seulement la mesure de la hauteur des arbres inventoriés dans la placette à rayon variable. Les propriétés de l’estimateur sont démontrées pour un peuplement feuillu mélangé situé dans la partie sud des Appalaches en Caroline du Nord, aux États-Unis.

Document Type: Research Article

Publication date: August 1, 2007

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  • Published since 1971, this monthly journal features articles, reviews, notes and commentaries on all aspects of forest science, including biometrics and mensuration, conservation, disturbance, ecology, economics, entomology, fire, genetics, management, operations, pathology, physiology, policy, remote sensing, social science, soil, silviculture, wildlife and wood science, contributed by internationally respected scientists. It also publishes special issues dedicated to a topic of current interest.
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