Crown cover estimate on ortho-photos and application of forest definition in forest inventories

Abstract

Forest area definition is the starting point for forest resource assessment and is one of the key issues in forest inventories. In this paper, the forest area definitions used for the first Italian National Forest Inventory (IFNI85) and that of the FAO – Forest Resources Assessment 2000 (FRA2000) have been compared analysing a sample of photo-plots distributed on different regions of Italy. The differences between the forest proportions obtained applying the two definitions, due to the different minimum threshold values of crown cover and of forest size, were very little, approximately 1%. Crown cover for each sample has been computed digitizing crown limits in GIS environment to reliably assess if minimum coverage threshold was met for each classification. Moreover, the lower cover threshold value of the FAO definition makes more difficult the classification of open areas. The applicability of reliable and less time consuming procedures for crown cover measuring, based on dot grids has been evaluated. The crown cover values estimated by dot grids were similar to those obtained digitizing crown limits on the ortho-photos. This study showed that the use of the FRA2000 definition of forest for the new national forest inventory should not significantly affect the comparisons of the new inventory data with the oldest ones (IFNI85 data), moreover the new data would be comparable on the international level.