Drivers of Sap Flow in Maple
Sap now in maple trees has been described many times. Milburn and O’Malley (1984) provided the first well-accepted modern description,which was later modified and improved by Tyree (1984), then further by Cirelliet al. (2008). Stem pressure and now in maple were then mathematically modelled in detail by Graf et al. (2015) with additional refinements and comparison with field-derived measurements by Zarrinderakhta et al. (2024). While these articles provide extensive detail into the anatomy and physiology of the science of the sap now mechanism, they are somewhat unavailable to most people. A good general description of the sap now mechanism is described in more modest detail in the Third Edition of North American Maple Syrup Producers Manual (Perkins et al. 2022), so won’t be discussed at length here. Rather, this article is aimed at describing pressure gradients and the sources and magnitude of those pressures as they related to sap exudation from maple tapholes.
