TREEFALLS, CROWN ASYMMETRY, AND BUTTRESSES

1 Crown asymmetry may have important consequences for forest dynamics. Previous research has shown that the tendency for tree crowns to grow laterally away from neighbours was associated with increased tendency for gap-edge trees to fall into pre-existing gaps. 2 We report the fa tes over a 6.7-year period of 127 trees whose crown shapes had been ma pped previously in a tropical broad-leaved forest in Panama. We demons trate directly that trees tended to fall on their heavy sides, and tha t more asymmetrical trees were more likely to fall than less asymmetri cal trees. 3 Using data from two different forests (in Panama and Cost a Pica) we also show that buttress formation is greatest on the sides of trees away from the direction of crown asymmetry, supporting the hy pothesis that buttresses in tropical trees serve at least partly as te nsion elements. There was only a weak tendency to produce buttresses o n the windward sides of trees. 4 However, (smaller) buttresses do occu r on all sides of trees, and buttresses grow in height more quickly th an the trees they support. We suggest that an additional function of b uttress formation in tropical trees is to reduce the effective bole le ngth and therefore reduce the risk of structural failure due t bucklin g.