Do invasive trees have a hydraulic advantage over native trees?
The hypothesis was tested that invasive trees have hydraulic traits that contribute to their invasive nature. Five pairs of co-occurring invasive and native trees, in mesic habitats, were selected: (1) Tamarix ramosissima and Salix amygdaloides; (2) Robinia pseudoacacia and Alnus rhombifolia (3) Schinus terebinthifolius and Myrica cerifera; (4) Ligustrum sinense and Acer negundo; and (5) Sapium sebiferum and Diospyros virginiana, respectively. Resistance to cavitation (the water potential [Ψx] at 75% loss of hydraulic conductivity [Ψ75]) was not consistently greater for invasive compared to native species (Ψ75=-1.91 and -1.67 MPa, respectively). Xylem specific conductivity (Ks), a measure of xylem efficiency, was not different between native and invasive species (Ks=3.50 and 3.70 kg s-1 MPa-1 m-1, respectively). The lack of difference for resistance to cavitation among invasive and native species suggests that the sampled invaders are not more tolerant to water stress than co-occurring native species. Apparently the spread and invasive nature of the sampled species cannot be explained by hydraulic traits alone.