Forests are changing in response to global change, with increased winter temperatures a critical driver. Warmer winter temperatures can allow range expansions for species currently limited by cold. Lianas may respond more favorably to warmer winters than trees because of their hydraulic characteristics, particularly larger vessels that are subject to cavitation. Temperate lianas pose serious treats to forest composition and functioning, and these influences may intensify with climate change. Although temperate lianas are suggested to be restricted by cold temperatures, the cold tolerance of trees and lianas has not been systematically compared. Furthermore, successful seed dispersal is essential for species to track climate change, and dispersal mode can relate to movement success. Here we ask whether cold tolerance and dispersal mode vary between lianas and trees, and whether these differences give lianas an advantage over trees under future conditions. To assess regional dispersal patterns of trees and lianas, we examined the prevalence of bird dispersal between state floras created from the USDA Plants database. To test if lianas were less cold tolerant than trees, twigs from trees and lianas were exposed to several cold temperature treatments in the spring and the resulting tissue damage was compared.
Results/Conclusions
Taxonomic diversity and dispersal mode varied between tree and liana floras across the 32 eastern most U.S. states. Diversity of both lianas and trees decreased with latitude, and from Florida to Minnesota the number of genera decreased from 88 to 10 for lianas and 315 to 52 for trees. Lianas were predominantly fleshy fruited, while trees were predominantly non-fleshy. The one exception was for Florida, which exhibited the opposite pattern presumably due to the influence of tropical species. Across the latitudinal gradient, the distribution of dispersal modes changed considerably for lianas but not trees. With increasing latitude, the percentage of the flora with fleshy fruits decreased from 45 to 33% for trees and increased from 50 to 90% for lianas. The high prevalence of fleshy fruits among lianas suggests that liana species may be less limited by dispersal than trees. Preliminary data on the cold tolerance of liana and tree tissue indicate substantial variability between species, but lianas tend to be less cold tolerant than trees. As winters continue warming, temperature limitations on liana populations may become relaxed and allow species to expand within and among forest patches on the landscape.