Figure 1. Stand regions and moisture conditions across eastern United States deciduous forests. Aridity index values are mean Aridity Wetness Index (calculated as the fraction of mean annual precipitation to mean annual evapotranspiration) at 9 m spatial resolution from 1970–2000. Aridity index data were accessed from the CGIAR-CSI GeoPortal at https://cgiarcsi.community (Trabucco & Zomer, 2009).
Figure 2. Embolism thresholds across forest stands. Panel (a) and (b) are mean P12 and P50 values ( \(\pm\)SE), respectively. Numbers above bars are sample size. Groups of bars not sharing the same uppercase letters denote significant differences among species determined by a two-way ANOVA with species and age as fixed factors and region as a blocking factor (Table 2).
Figure 3. Test of simple effects of significant interaction terms from two-way ANOVA by pairwise comparison of least square means. Panel (a) is least square mean P50 ( \(\pm\)SE) across forest ages for each species. Panel (b) is least square mean P50 ( \(\pm\)SE) across chronosequence regions for each forest age. Groups of bars not sharing the same uppercase letters denote significant differences of main effects at α = 0.05. Within groups, bars not sharing the same lowercase letters denote significant differences at α = 0.05.
Figure 4. Mean xylem lumen area ( \(\pm\)SE) across chronosequences (Panel (a)) and age (Panel (c)). Groups of bars not sharing the same uppercase letters denote significant differences (p ≤ 0.05) between species, while bars within groups not sharing letters denote differences within species among ages or chronosequences from a two-way ANOVA with species and age as fixed factors. Panels (b) and (d) show the relationship between mean lumen area and mean specific embolism threshold of individual trees assessed by linear regression. Lines are best fit from linear regression when slope is significant (p < 0.05).
Figure 5. Mean vessel density ( \(\pm\)SE) across chronosequences (Panel (a)) and age (Panel (c)). Groups of bars not sharing the same uppercase letters denote significant differences (p < 0.05) between species, while bars within groups not sharing letters denote differences within species among ages or chronosequences from a two-way ANOVA with species and age as fixed factors and region as a blocking factor (Table 2). Panel (b) and (d) show the relationship between mean lumen area and mean specific embolism threshold of individual trees assessed by linear regression. Lines are best fit from linear regression when slope is significant (p < 0.05). Solid lines are best fit across species and dashed line is at the species-level.
Figure 6. Midday leaf water potential (ΨL) behavior across species and stands. Panel (a) is ΨL interquartile range in each respective stand. Box‐plots show the median (middle line), interquartile range (box), and maximum/minimum value (whiskers), except where values exceed 1.5 times the interquartile range (points). Numbers above boxes are sample size. Panel (b) is mean interquartile range ( \(\pm\)SE) for each species. Bars not sharing the same uppercase letters denote significant differences across species by a two-way ANOVA with species and age as fixed factors.
Figure 7. Relationship between hydraulic safety margin (Ψsafety) and ΨL interquartile range. Panel (a) is safety margin at P12 (Ψsafety,P12) and Panel (b) is safety margin at P50 (Ψsafety,P50). Solid lines are best fit linear regression (least square means) across species when slope is significant (p < 0.05). Error bars are the minimum and maximum Ψsafety from100 simulated Ψsafety data points calculated from the lowest 10% of ΨL and the middle 60% of Ψthresh from 50,000 bootstrapped samples for each species and each site (section 5.6).