Eastern hemlock transpiration: patterns, controls, and implications for its decline in southern Appalachian forests
Eastern hemlock, a principal riparian and cove canopy species in the southern Appalachian mountains, is facing potential widespread mortality due to the hemlock adelgid (HWA). To estimate the impact that the loss of this species will have on forest transpiration (E1) we quantified whole-tree (Ec) and leaf-level (E1) transpiration over a range of tree sizes (9.5 - 67.5 cm or 3.7 - 26.6 in) during 2004 and 2005. Maximum rates of Ec varied by a diameter, with large tree transpiring a maximum of 186 kg (or 49 gal) water tree-1 day-1. Large trees had higher maximum rates of instantaneous El compared to small trees (1.99 versus 1.54 mmol m-2s-1). with increasing HWA infestation, regardless of leaf area, trees are expected to have declining transpiration rates. Hemlock mortality could reduce annual- and winter-spring E1 by 10 and 30 percent, respectively. The lack of an evergreen riparian canopy species will alter the dynamics of E1 and stream discharge.