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Compensating for missing plot observations in forest inventory estimation

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Abstract:

The Enhanced Forest Inventory and Analysis program of the U.S. Forest Service has established a nationwide array of permanent field plots, each representing approximately 2400 ha. Each plot has been assigned to one of five interpenetrating, nonoverlapping panels, with one panel selected for measurement on a rotating basis each year. As with most large surveys, observations for some plots are not obtained. Several techniques for dealing with missing observations were compared with respect to the bias and precision of stratified estimates of mean volume per unit area using data from the State of Indiana in the north-central region of the United States for illustrative purposes. For the proportion of missing plots ranging from 1% to 10%, acceptable results were obtained for techniques that both ignored and replaced missing plot observations, but only when the techniques accounted for differences between plots in private and public ownerships.

Le programme amélioré d'inventaire forestier et d'analyse du Service forestier des États-Unis a permis d'établir un dispositif national de placettes permanentes. Représentant approximativement 2400 ha, chaque placette a été assignée à l'un des cinq groupes qui s'interpénètrent sans chevauchement. Chaque groupe est sélectionné à tour de rôle pour être mesuré sur une base annuelle. Comme dans tous les inventaires à grande échelle, les observations de certaines placettes manquent. Pour résoudre ce problème d'observations manquantes, plusieurs techniques ont été comparées quant au biais et à la précision des estimations stratifiées du volume moyen par unité de surface, en utilisant à titre d'exemple les données de l'État de l'Indiana situé dans le centre nord des États-Unis. Lorsque la proportion des placettes manquantes se situe entre 1 et 10 %, des résultats acceptables ont été obtenus tant par les techniques qui ignorent que celles qui remplacent les observations des placettes manquantes, mais seulement lorsque ces techniques tiennent compte des différences entre les placettes sur les terres publiques et celles sur les terres privées.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: 2003-10-01

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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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