6.1 Spatio-temporal variation in embolism vulnerability
We found little variation in embolism vulnerability across stands, though embolism thresholds were markedly different across species (Fndf,ddf = 149.87, p = 0.001 for P12, andFndf,ddf = 169.62, p = 0.003 for P50, Fig. 2). At the P50 threshold, we detected some variability arising from the interaction between species and age (Fndf,ddf =18.88, p = 0.017, Table 2) and age and region (Fndf,ddf = 21.312, p = 0.016, Table 2). Specifically, we found that A. saccharum P50 differed between young (15yo) and intermediate (35yo) stands, although embolism vulnerabilities were invariant across stand ages for Q. alba andL. tulipifera (Fig. 3a). Additionally, across all species, young stands (15yo) had more vulnerable xylem in the mesic NC_W stands than in the drier IN and NC_E stands; however, this pattern was not observed for the 35yo and 85yo age classes (Fig. 3b). In general, Q. albahad the most vulnerable xylem while A. saccharum had the least (Fig. 2). Mean P12 across all stands were −1.09 MPa (SE = 0.06), −1.65 MPa (SE = 0.10), and −2.75 MPa (SE = 0.20) and mean P50 was −2.72 MPa (SE = 0.09), −3.91 MPa (SE = 0.12), and −4.77 MPa (SE = 0.18) forQ. alba, L. tulipifera, and A. saccharum , respectively.