Thursday, August 7, 2008

PS 68-167: Sycamore (Platanus occidentalis) support more lianas than expected in southwestern Ohio floodplain forests

James R. Milks, Justin Hibbard, and Thomas P. Rooney. Wright State University

Background/Question/Methods: Lianas are structural parasites that depress growth, fertility and survival rates of their hosts, but the magnitude to which they alter these rates differs among host species. We tested the hypothesis that sycamore would have fewer creeping lianas because it possesses exfoliating bark and is therefore able to shed lianas from the trunk. We investigated the distribution of lianas on the trunks of trees > 6 cm DBH in floodplains throughout the Miami River Valley (southwestern Ohio). We recorded the identity and DBH of each tree species and counted the number of creeping lianas present on the trunk at 1.6 m in height in 10 x 300 m belt transects conducted along 3 river stretches. We generated expected frequencies lianas per tree based on the relative surface area available per tree species, and analyzed data using replicated goodness of fit tests. Our analysis includes 875 lianas (mostly Toxicodendron radicans) and 730 trees.
Results/Conclusions: Contrary to predictions, sycamore trees had 32% more lianas than would be expected based on chance alone (G pooled = 29.04; df = 1; P < 0.001). Also to our surprise, box elder (Acer negundo) had only half of the lianas as would be expected based on chance (G pooled = 44.39; df = 1; P < 0.001). We find no support for our hypothesis that bark exfoliation protects sycamore trees from the lianas in our study area, and hypothesize bark chemistry may enable box elder to suppress liana growth on its trunk.