S2In the spring of 1967, a vacuum pump was installed at a sugarbush located in Underhill, Vermont. This work proceeded in two phases: an individual-tree study designed to determine if sap could be drawn out of a tree in sufficient quantities to account for large yield differences; and a large-scale study of the effects of sustained levels of vacuum on yields from a nearly commercial-size network of tubing. S3.

S2When sap production research was begun by the Northeastern Forest Experiment Station in Burlington, Vermont, in 1964, it became apparent that more quantified information on sap yield variation among individual trees and among years was needed to facilitate the designing of efficient experiments. One of the first projects undertaken was to record seasonal sap yields on approximately 140 individual trees on a sugarbush near Jericho, Vermont. Yields were measured in the sap seasons of 1965, 1966, and 1967. Data presented in this report are based for the most part on a random sample drawn from these trees. All sample trees were tapped with two tapholes bored to a uniform depth.S3.

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