Bark water vapor conductance varies among temperate forest tree species and is affected by flooding and stem bending.

Abstract

Bark water vapor conductance (gbark) modulates forest transpiration during droughts, when leaf transpiration is highly reduced. If disturbances such as windstorms and floods impact gbark, they could affect tree performance during subsequent droughts. Bark traits, particularly lenticel traits, likely drive variation in gbark and may influence the effects of disturbances on gbark. We assessed variation in gbark and bark traits in tree branches of 15 tree species in a temperate forest in Louisiana, USA, and performed experiments to test whether gbark in tree branches was affected by bending (simulating wind) and whether gbark of tree saplings was affected by soil flooding. Among tree species, mean branch gbark ranged from 2.22 to 12.02 mmol m-2 s-1. Stem bending increased gbark by 23% compared to unbent controls. Although gbark was unaffected by 38 days of flooding, after 69 days post-flood it was reduced by 41% compared to unflooded controls. The relationships between gbark and bark traits, including bark thickness, lenticel density, and lenticel size, were inconsistent across the survey and experiments. Together, these results show that gbark is variable among species and mutable. Uncovering the drivers of gbark variation within and among trees, including exposure to extreme weather events, will inform projections of forest dynamics under climate change.