On research priorities to advance understanding of the safety–efficiency tradeoff in xylem: A response to Bittencourt et al.'s (2016) comment 'On xylem hydraulic efficiencies, wood space‐use and the safety–efficiency tradeoff'. Issue 4 (27th June 2016) - Gleason, Sean M.; Westoby, Mark; Jansen, Steven; Choat, Brendan; Brodribb, Tim J.; Cochard, Hervé; Delzon, Sylvain; Hacke, Uwe G.; Jacobsen, Anna L.; Johnson, Daniel M.; Lens, Frederic; Maherali, Hafiz; et al.