iForest - Biogeosciences and Forestry


Estimation of stand crown cover using a generalized crown diameter model: application for the analysis of Portuguese cork oak stands stocking evolution

Joana A Paulo   , Sónia P Faias, Célia Ventura-Giroux, Margarida Tomé

iForest - Biogeosciences and Forestry, Volume 9, Issue 3, Pages 437-444 (2015)
doi: https://doi.org/10.3832/ifor1624-008
Published: Dec 02, 2015 - Copyright © 2015 SISEF

Research Articles

A generalized non-linear tree crown diameter model was developed with the aim of allowing the computation of tree crown diameter over a large range of tree dimensions, and allowing its inclusion in forest growth and yield models. The model was formulated to provide biological meaning to the predicted values. Due to the nested structure of the data analyzed (trees within stands), both mixed- and fixed-effect models were developed. Since tree crown diameter is not frequently measured in forest inventories, the validation of the mixed model was carried out by considering the population specific response. The results demonstrate that when the measurements required for the mixed model calibration are not available, the use of the fixed effect model results in less biased and more accurate estimates. The fixed model was applied to the data from the two last Portuguese National Forest Inventories (NFI) to analyze the change in stand crown cover and assess the stocking evolution of cork oak stands in Portugal between 1996 and 2006. Results showed an increase in the frequency of stands with crown cover lower than 20%, as well as a decrease in the frequency of stands with crown cover between 20 and 40%. Average crown cover values were significantly different in the two NFI, with a decrease from 28.0 to 26.5% over the considered period.


Quercus suber, Stand Crown Cover, Tree Crown Diameter, Nonlinear Mixed Effects Model, Nonlinear Fixed Effects Model, Portuguese National Forest Inventory

Authors’ address

Joana A Paulo
Sónia P Faias
Célia Ventura-Giroux
Margarida Tomé
Universidade de Lisboa, Instituto Superior de Agronomia, Centro de Estudos Florestais, Forest Ecosystem Management under Global Change research group (ForChange), Tapada da Ajuda, 1349-017 Lisbon (Portugal)

Corresponding author

Joana A Paulo


Paulo JA, Faias SP, Ventura-Giroux C, Tomé M (2015). Estimation of stand crown cover using a generalized crown diameter model: application for the analysis of Portuguese cork oak stands stocking evolution. iForest 9: 437-444. - doi: 10.3832/ifor1624-008

Academic Editor

Rupert Seidl

Paper history

Received: Feb 27, 2015
Accepted: Jul 28, 2015

First online: Dec 02, 2015
Publication Date: Jun 01, 2016
Publication Time: 4.23 months

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