This paper presents a method for automatic extraction and characterisation of vegetation structures (such as trees, shrubs, hedges or lawns) in high density urban areas. We present a hierarchical strategy to extract, analyze and delineate vegetation areas according to their height. Spectral indices are used to detect urban vegetation areas. We differentiate lawns from treed areas by computing a texture operator on the digital elevation model (DEM) corresponding to the vegetation areas previously detected. A robust region growing method based on the DEM is developed for an accurate delineation of tree crowns. We evaluate the accuracy of the tree crown delineation results to a reference manual delineation. Results obtained are discussed and the influential factors are put forward.