L'inventaire par évaluation visuelle de grosseurs d'arbres, une alternative pertinente aux inventaires forestiers complets

Abstract

The inventory technique using visual evaluation is based on a systematic sampling method with a high survey rate (25 to 40%). It is proposed as a promising alternative to complete inventories for the characterisation of mixed broadleaved uneven-aged stands. Trees located within 0.1 ha sampling plots are visually graded into large size categories. Two modalities of this inventory method, using one or two operators (IGVE1 or IGVE2), have been compared with two other methods: the classical complete inventory (CI) and a systematic sampling inventory with girth measurement (SIGM). The calculations are based upon experimentations carried out in a coppice with standards. No significant difference has been detected between IGVE1, IGVE2 and the complete inventory, concerning number of trees and basal area estimations, considered globally or by girth classes. However, IGVE1 compared with SIGM, provides a slight, but significant, underestimation (5%) of the number of trees. This is mainly observed in the sampling units comprising a high number of small trees. Nevertheless, inventory method with girth visual evaluation can be considered as a very useful tool for the description of unevenaged mixed broadleaved stands, namely during the stage of analysis of management plans. Furthermore other information useful for the preliminary phase of a forest management (description of regeneration, health status of trees, ...) can also be collected during the same inventory, and a thematic mapping of the results is possible at the stand level. © INRA, EDP Sciences, 2005.