Maples under pressure
How sap pressure and flow interacts in maple trees during the sugaring season.
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Root pressure in trees: a spring phenomenon
Root pressure occurs when the soil begins to warm, and when snow has melted, and icy water from snow melt has largely drained from the soil, forest soils warm quickly.
Why Does the Sap Stop Running After a Few Days if it Doesn’t Freeze Again?
Without a freeze, the flow of sap will continue to slow and eventually stop because there is no longer a difference between the pressure inside and outside of the tree. However, producers often observe an uptick in sap flow during the daytime over a few days. Why does this occur? Where did the extra sap come from? Typically, these short bursts of increased sap flow happen when the temperature warms over the next few days. The warm temperature causes gas bubbles in the wood fibers to expand and squeeze more water from the wood tissues, where it flows into the vessels and out through the taphole. This might occur for a couple of days, and eventually turn into slow weeping flows before ceasing entirely.
Why sap may not always flow well in early season
Maple producers know that when the temperature starts to rise in the spring, sap flows can’t be far behind. But when the weather starts to warm early in the spring and temperatures seem favorable for good sap flows, they are sometimes left wondering why the sap hasn’t started to run. There are several explanations for the disconnect between warm air temperature and a lack of flow during
the early season.