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).