7. Discussion
We tested three hypotheses to assess variability and coordination of key plant hydraulic traits across ten deciduous forest stands. We found little support that stand age and hydroclimate influenced relative xylem vulnerability (hypothesis 1 & 2). While we detected some region and age effects, variation in vulnerability to embolism was principally determined by the large species effect. Additionally, we found little support for hypothesis 3, which predicted stricter ΨLregulation would be associated more vulnerable xylem. Contrary to the prevailing expectation, we found that the more anisohydric Q. alba possessed stem tissues more vulnerable to embolism than their more isohydric counterparts. Moreover, we found that Q. alba had small or negative Ψsafety and a high degree of estimated native embolism such that its loose regulation of ΨLlikely occurred with a substantial hydraulic cost.