e-Publications@Marquette

The impact of lianas on tree dynamics and forest regeneration, and the question whether lianas can redirect tropical forest succession from tree-dominated to liana-dominated ecosystems, are of profound importance for the potential impact of global change on long-term tropical forest health and the maintenance of species diversity. Growing evidence suggests that lianas can substantially alter tropical forests by disrupting tree regeneration and thus altering species diversity and forest carbon sequestration. Because liana abundance and biomass are increasing in neotropical forests, studies on the ecology of lianas and their role in tropical forests are now critical. In this project, we are testing a series of interrelated hypotheses to determine whether lianas can set in motion a positive feedback process whereby tropical forests are driven toward permanently liana-altered structure, species composition, and reduced tree density, diversity, and biomass. To accomplish test these hypotheses, we permanently tagged, spatially mapped, measured the diameter, and identified all lianas > 1 cm diameter in a 50 hectare plot of tropical forest on Barro Colorado Island, Panama. We have combined this demographic study with a controlled liana removal experiment to gain a more mechanistic understanding of liana-tree interactions. n 2007 we finished a full census of all of the lianas > 1 cm on the 50-ha plot on Barro Colorado Island (BCI). In total, we are following more than 68,000 rooted lianas comprising 163 species. Some of our preliminary findings demonstrate that lianas substantially reduce tree growth and survival, and that trees with a high degree of liana infestation in their crowns tend to have twice the probability of dying than trees with little or no liana infestation. In treefall gaps, which have been called the engines of regeneration for tropical forests, lianas suppress tree recruitment, growth, regeneration and diversity, and thus may have a widespread impact in tropical forests. Finally, we found that lianas are increasing in abundance and biomass rapidly on BCI, and the proportion of trees with lianas in their crowns, as well as the severity of liana infestation, are far higher now than 40-years ago – a pattern that is consistent with other neotropical forests.