5.1 Study sites
We selected ten forest stands across four regions in the eastern US that
spanned a hydroclimatological gradient (Fig. 1, Table 1). Four of the
stands were ~85-year-old temperate deciduous forest
AmeriFlux sites (US-MMS, US-CWT, US-Dk2, and US-MOz) in the states of
Indiana (IN), North Carolina (NC), and Missouri (MO). The gradient
approach allowed us to understand how key plant hydraulic traits varied
as a function of climate. Additionally, the ~85-year-old
stands in IN and NC were each end-members of a chronosequence (including
~15- and ~35-year-old stands co-located
within 20 km of the ~85-year-old stand). The
chronosequences in NC and IN allowed us to investigate how the
relationship between ΨL behavior and vulnerability to
hydraulic failure varied with stand age in regions experiencing a
similar climate.
Indiana chronosequence
stands:
The ~85-year-old (IN 85yo) (39° 19’ 23.52”, -86° 24’
47.16”) and ~35-year-old (IN 35yo) (39° 19’ 19.87”, -86°
28’ 51.92”) IN stands were located in Morgan-Monroe State Forest.
Dominant species were A. saccharum, L. tulipifera, Q. alba,
Sassafras albidum Nutt., Quercus rubra L., and denseLindera benzoin L. understory (Roman et al ., 2015). Deep
silt clay loam soils characterized the sites (90–120 cm). The
~15-year-old stand (IN 15yo) (39° 13’ 10.93”, -86° 32’
30.96”) was a nearby (<20 km) regenerating planting with
similar species composition located at The Indiana Research and Teaching
Preserve’s Bayles Road site. There, 5-year-old saplings of common
Indiana forest tree species from local forest seed stock were planted in
2006 at a spacing of 5.25m \(\times\) 5.25m and in random 12 \(\times\)12 arrangements (Flory & Clay, 2010).