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Figure S1. Relationship between P50 and percent loss of conductance for diffuse-porous species. The relationship was strenghtened when tested with PICs (12=0.54, P=0.035).

Figure S2. Relationship between wood density and leaf water potential for four sites exhibiting a range in drought stress (a, b); water potentials were measured during the most intense drought period studied. Relationship between wood density and leaf water potential at the driest site, for three dates over a period of lessening drought conditions in 2007.

Figure S3. (a) Relationship between P50 and midday leaf water potential for the four sites. Water potentials were measured during the most intense drought period studied, prior to any rain. P50 is the xylem water potential at which 50% loss of conductivity is observed. (b) The midday safety margin against excessive embolism (ψmd-P50), calculated for diffuse-porous species. Site codes, in order of increasing water deficit are LRW, Lake Raleigh Woods; SCB, Swift Creek Bluffs; HB, Hemlock Bluffs; BP, Bond Park.

Figure S4. Vulnerability curves used to determine P50, the water potential at which conductivity is reduced to 50% of maximum. Data for the remaining species were obtained from the literature. We also determined maximum vessel length of each of these species. To do this, five branches of approximately 60 cm were flushed with distilled water for 10 min at 100 kPa. One end of the branch was then attached to a source of compressed air at 100 kPa while the other end was progressively shortened by removing sections of 1–2 cm until air was observed to exit the cut end. Only for Oxydendrum arboreum did mean maximum vessel length (32.6 cm) exceed the length of the branches used to determine vulnerability (25 cm). For the remaining species, vessel lengths ranged from 11.8 cm (Viburnum nudum) to 19.8 cm (Prunus serotina).

Table S1. Data summary of the study species. Xylem is categorized as diffuse porous (DP) and ring porous (RP). Phenology is categorized as partial drought deciduous (D) and not drought deciduous (N). Two species, F. americana and P. serotina, exhibited very limited amounts of leaf senescence during the drought, and are classified here as not drought deciduous. WD is wood density. PLC08 and PLC07 are percent loss of conductivity in the non-drought year (2008) and the drought year (2007). Slope is the slope of the relationship between ln(gs) and leaf WP. Midday water potential are mean values at each site for the period of most intense drought. Mortality, PLC, and desiccation are mean values from the two driest sites (HB and BP).

Table S2. Percent loss of conductivity (%) of three species at three dates of lessening drought intensity. There was no evidence of recovery of conductivity by the end of the season despite substantial amelioration of drought conditions. The first sampling date was in the peak of drought conditions, the second date followed a 39 mm rainfall event, and the last date followed several days of rainfall totaling 142 mm.

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