The impact of season of harvest and duration of pre-measurement storage impact hydraulic conductance of stem samples for Acer rubrum L. x saccharinum L. and Fraxinus americana L.

The influence of pre-measurement storage length and season of harvest of stem segment samples on hydraulic conductance and percentage embolism was determined for two tree species because no published guidelines exist concerning storage. Stem sections from Fraxinus americana L. 'Autumn Applause' (white ash) and Acer rubrum L. x saccharinum L. 'Autumn Blaze' (hybrid red maple) were collected from well-established trees in fall 1995 (October), spring 1996 (April), and summer 1996 (July). Ends of stem sections collected in the fall were either covered with wax or left exposed. Entire sections from all dates were placed in closed plastic bags to prevent desiccation during transport and subsequent storage. Stem sections were either analyzed immediately (0 storage) or held at 2 degrees C for 2 or 4 days. Hydraulic conductance before embolisms were cleared with positive pressure (initial k(h)), hydraulic conductance after embolisms were cleared (maximum k(h)), and percentage embolism were similar for all pre-embolism measurement storage lengths within each of the three seasonal sampling periods for hybrid red maple and spring- and summer-collected white ash. Fall-collected white ash samples with 0 storage had higher initial k(h), and percentage embolism increased if samples were stored. Embolism was greatest for summer-collected samples and lowest for spring-collected samples for hybrid red maple, but values were similar for white ash. Stem covering did not influence measured parameters. Our data indicate that hybrid red maple stem segments can be stored without significant loss of hydraulic conductance for up to 4 days, but white ash should not be stored in the fall. Unless maximum levels of native embolism have been reached, as determined from laboratory analysis, stem segments of species on which storage data are not available should be processed as soon as possible.