Long-term ecological monitoring has revealed an increase in tropical liana (woody vine) abundance over the course of the past two decades.  Lianas have a substantial effect on adult tree recruitment, growth, reproduction, and mortality, but few studies have experimentally compared the relative competitive effects of lianas vs. trees on tropical forest dynamics.  Because liana abundance and biomass appear to be increasing, their unique effect on tree seedling recruitment may have future implications for tropical forest species composition. We experimentally cut an equal biomass of lianas and saplings at 10 sites in central Panama.  At each site, we tracked four experimental plots to compare the effects of (1) liana removal, (2) sapling removal, and (3) no-manipulation controls paired with each removal category.  We planted forty 3-month-old seedlings of Lacmellea panamensis, Dipteryx oleifera, and Apeiba membranaceae into each plot and recorded seedling survival and growth over a 2-year period.
Results/Conclusions

The presence of both lianas and saplings significantly reduced light levels in the forest understory, although saplings had a more consistent effect across seasons.  Seedling survival was also highest and most consistent in sapling removal plots, although not significantly different than liana removal plots.  Of those seedlings that survived, seedling RGR was highest in both removal treatments, and fastest in A. membranacea.  However, post-hoc Tukey tests showed that there were no differences in seedling RGR between different species or removal treatments during the dry seasons of 2008 or 2009, but that D. oleifera grew most in both removal treatments during the wet seasons of 2008 and 2009.  Based on previously published work documenting liana-specific effects on water availability at these sites, paired with our light level measurements, we propose that lianas and saplings have very similar effects on seedling regeneration at this local size scale, but that the mechanism for this effect may be unique to growth form.