5. Materials and Methods
5.1 Study sites
We selected ten forest stands across four regions in the eastern US that spanned a hydroclimatological gradient (Fig. 1). Four of the stands were ~85-year-old temperate deciduous forest AmeriFlux network 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 regulation and vulnerability to hydraulic failure varied with stand age in regions experiencing a similar climate.