Determination of the spatial distribution of trees from digital aerial photographs Janne Uuttera * , Arto Haara, Timo Tokola, Matti Maltamo The University of Joensuu, Faculty of Forestry, P.O. Box 111, FIN-80101 Joensuu, Finland Received 18 November 1997; accepted 17 March 1998 Abstract This study examined the possibilities of using computerized digital aerial photograph interpretation in determining the spatial distribution of trees. The material of the study included eight mapped stands in the municipality of Hyytia Èla È (61850 0 N and 24818 0 E), in southern Finland. The aerial photographs used were taken in June 1995 at a scale of 1:5000. Two approaches for determining the spatial pattern of trees were used. Firstly, in the point-process based approach used in this study, the individual trees in the digital aerial photograph were segmented by a robust segmentation method, based on recognition of the pattern of tree crowns with sub-pixel accuracy. Secondly, the crown coverage was determined by region growing segmentation combined with active surface representation. The signi®cance of the differences in the means of image coverage pattern indices between the various spatial distribution categories was tested with one-way variance analysis. Because the process misclassi®ed clustered spatial patterns as regular patterns, and regular patterns as random patterns, the usability of digital aerial photographs seems to be limited for the point-process based determination of the spatial pattern of trees if the scale is 1:5000 or less. When image coverage pattern indices were applied, the differences in the means of the spatial distribution categories proved not to be clearly statistically signi®cant due to the great variation within classes. However, interpretation of crown coverage could have applications in practical forestry due to the low resolution requirements for the images used. # 1998 Elsevier Science B.V. Keywords: Aerial image; Digital image analysis; Spatial pattern; Stand structure 1. Introduction Besides species composition and the size distribu- tion of trees, stand structure is characterized by the spatial distribution of trees. Tree locations may be regularly distributed, randomly distributed, clustered or a combination of these three categories (e.g. Tomppo, 1986). There is a considerable natural varia- tion in the spatial distribution of trees between and within stands, caused by site variation, damages, rocks, swampiness and other factors (Pukkala, 1988). In addition to natural variation, the silvicultural operations that have the greatest impact on the vertical structure and species composition of a stand, affect also the spatial distribution of trees within the stand. Lack of information on the spatial distribution of trees in management planning may result in biased growth prediction and thinning proposal (Pukkala, 1990). In a clustered stand, growth prediction tends Forest Ecology and Management 110 (1998) 275±282 *Corresponding author. Tel.: +358 13 251 4414; fax: +358 13 251 4444; e-mail: juuttera@forest.joensuu.fi 0378-1127/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved. PII S0378-1127(98)00292-8