The \changing dynamics of tropical forests hypothesis\ attributes recent increases in tree turnover rates tree basal area and lianas to rising concentrations of atmospheric CO2 (Phillips and Gentry 1994 Phillips et al. 1998 2002a). The relative importance of large lianas (woody vines) increased by 100% for stem enumerations conducted during the 1980s and 1990s in widely scattered Neotropical forests. We use three independent types of data to evaluate the hypothesis that lianas have increased in importance in old growth forests on Barro Colorado Island Panama. Liana leaf litter production and the proportion of forest-wide leaf litter composed of lianas increased between 1986 and 2002. In contrast liana seed production and liana seedling densities were much more variable through time with particularly high levels during and immediately after El Niv±o years. Longer time series will be required to detect shifts in life-form composition for highly dynamic seed and seedling communities. The Barro Colorado Island leaf production data are however consistent with the hypothesis that lianas are increasing in importance in Neotropical forests.