Three-dimensional structure of a mixed broad-leaved forest in Japan

Abstract

An investigation was made in a mixed broad-leaved forest in Japan to determine the three-dimensional structure of the crowns of the component species. Vertical extensions and positions of foliage above a circle with a 20-cm diamter on the forest floor were measured using a grid of 177 points in the forest. The first leaf layer above a point was defined to be the highest aggregation of the foliage above the point, and the second leaf layer to be the one below. There were generally two leaf layers above each point, the first and the second. Each of the nineteen species in the plot belonged to either the first leaf layer or the second. Because the leaf layers varied in height from place to place in the forest, the two leaf layers were not separated clearly. Mean vertical depth of each leaf layer was about 2 m irrespective of the leaf layers and component species. Since the depths were similar among the species, species mean crown volumes (volumes of the spaces occupied by foliage) per unit land area mainly depended on horizontal extensions of their crowns, or the coverage. That is, species varied in their horizontal rather than vertical crown extensions. There was an upper limit (6 m) to the sum of vertical depths of the leaf layers above a point on the forest floor. On an average, about three species occurred above a point.