Recent evidence suggests that liana abundance and biomass are increasing in Neotropical forests, representing a major structural change to these ecosystems. However, putative explanations for these increases remain largely untested. Over an 8-year period (1999 - 2007), we censused lianas in nine, 24 x 36 m permanent plots in old-growth and selectively logged forest at La Selva Biological Station in Costa Rica to test two hypotheses: (1) lianas abundance and basal area are increasing in this forest; and (2) vegetative recruitment is a large contributor to liana increases. We defined vegetative recruitment as lianas that were not present in 1999 or 2002, but had clearly entered and rooted in the plot from outside or above.
Results/Conclusions
We found that both mean density and basal area of lianas (>1cm diameter) increased by 15 and 20 percent, respectively, in the old-growth forest at La Selva, supporting the hypothesis that lianas are increasing in abundance in this forest. Vegetative recruitment contributed 7.3 and 60 percent to the increase in liana abundance and basal area, respectively, supporting the hypothesis that vegetative recruitment contributes substantially to liana increases in old-growth forests. In the selectively logged forest, however, neither liana abundance nor basal area increased, suggesting that the pattern of increasing lianas may be restricted to old-growth forest or masked by successional patterns. Our data support the hypothesis that lianas are increasing in abundance and biomass in old-growth forests, and that vegetative recruitment is a major contributor for these increases, particularly for liana biomass.