Abstract Different allometric relationships were established at the leaf, branch, stem and whole-tree levels for young poplar ( Populus) trees during their first and second year of growth. Five poplar clones were grown under an intensively cultured regime at two different locations, Afsnee (near Gent, Belgium) and Orsay (near Paris, France). Leaf area was related linearly or non-linearly (power or logarithmic functions) to parameters that can be measured easily and non-destructively, such as leaf length or width, stem or branch diameter, stem or tree height, and volume index. Only small differences in the basic allometric relationships were noticed between the two sites and the five clones. A very good agreement was observed between leaf area index ( LAI) values estimated from allometric relations and from indirect measurements using a plant canopy analyzer. These observations suggest that simple and general relations can be used to estimate LAI in young, high density poplar stands or leaf area at different organizational levels in trees.