Growing evidence suggests that one of the major contemporary changes in tropical and some temperate forests is the increase in the relative abundance and basal area of lianas (woody vines). Lianas constitute 10-45% of the woody stems and species in tropical forests and 5-15% of the above ground biomass (AGBM), reaching upwards of 30% ABGM in disturbed areas. More than any other growth form, lianas appear to have a disproportionately large impact on carbon dynamics in relation to their stand-level AGBM. As liana abundance and biomass increase, forest-wide carbon storage and sequestration may actually decrease, with heavy liana infestations inhibiting tree regeneration and reducing the total amount of carbon sequestered in tree biomass. Thus, it is critical to determine whether lianas are actually increasing in abundance and basal area and to quantify the extent of this increase. We used previously published studies, along with three of our own long-term datasets to examine whether lianas are indeed increasing in abundance and basal area in both temperate and tropical forests.
Results/Conclusions
Several published studies reported steep increases in liana abundance, basal area, and leaf and flower production in neotropical and subtropical forests. Using our own data, in which we tracked tagged liana individuals over long time periods, we found mixed results. After 10-years on Barro Colorado Island, Panama (1993 - 2003), we detected no significant change in liana abundance or basal area in sixteen 24 x 36 m plots. After 8-years at La Selva Biological Station in Costa Rica (1998-2006), liana basal area increased in nine of nine 24 x 36 m plots, but liana abundance did not increase over these 8 years. Recensusing lianas in 14 forests located in southeastern Wisconsin revealed no change in liana abundance or basal area over a 45-year period. In summary, our results were equivocal and they do not confirm the predicted and purported increases in lianas in temperate and tropical forests. Collectively, these contrasting results argue for the need for additional long-term datasets in a variety of sites to evaluate this question.
