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Evaluation of sampling alternatives to quantify tree leaf area

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Abstract:



High within- and among-tree crown variation have contributed to the difficulty of tree-crown sampling and single-tree leaf area (area available for photosynthesis) estimation. Using reconstructed trees, simulations were used to compare five sampling designs for bias, mean square error (MSE), and distribution of the estimates. All sampling designs showed nearly zero bias. For most sample trees, stratified random sampling resulted in the lowest MSE values, followed by ellipsoidal, two-stage systematic, simple random, and then by two-stage unequal probability sampling. The poor performance of two-stage unequal probability sampling can be ascribed to the unequal probability of inclusion of first-order branches and twigs.

La forte variation à l'intérieur et entre les cimes contribue également à la difficulté d'échantillonner la cime et d'estimer la surface foliaire (surface disponible pour la photosynthèse) d'arbres individuels. A l'aide d'arbres reconstitués, des simulations ont été utilisées pour comparer cinq techniques d'échantillonnage en termes de biais, de carré moyen résiduel (CMR) et de la distribution des valeurs estimées. Toutes les techniques d'échantillonnage ont montré un biais proche de zéro. Pour la plupart des arbres échantillonnés, l'échantillonnage aléatoire stratifié en fonction de la hauteur dans la cime a montré les valeurs les plus faibles de carré moyen résiduel, suivi par l'échantillonnage ellipsoïde, l'échantillonnage systématique à deux degrés, l'échantillonnage aléatoire et finalement l'échantillonnage à probabilité inégale à deux degrés. La mauvaise performance de la dernière technique d'échantillonnage peut être attribuée à la probabilité inégale d'inclusion des branches et des rameaux du premier ordre.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: January 1, 2003

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