SOURCES OF TEMPORAL VARIATION IN SAP SUGAR CONTENT IN A MATURE SUGAR MAPLE (ACER-SACCHARUM) PLANTATION

Temporal factors affecting sap sugar content (SSC) were assessed in a 65-yr-old plantation of sugar maple (Acer saccharum Marsh.) located in Quebec. A total of 694 maples were measured and the variation in SSC was assessed between 2 sampling years, among 3 days within each sugar season, and among hours within each sampling day. Average individual t ree variation in SSC was extensive, ranging from 1.3 to 5.5% Tor sprin g 1994, and from 1.4 to 4.8% for spring 1995. The correlation between DBH and SSC was weak for both sampling years. SSC did not vary extensi vely between sampling hours within days, while it varied significantly among sampling days for both years analysed. However, the largest sou rce of variation in SSC was between the 2 sampling years. Tree relativ e performances in SSC were moderately conserved among days within year s and to a lesser degree, between sampling years. The relative magnitu de of the differences between statistical treatments and the stability analysis of tree relative performances indicated that, for adequate e stimation of an individual tree's SSC, sampling over years appears sup erior to sampling over several days within a single sugar season. Also , sampling towards the end of the sugar season or during days with low er SSC appears less reliable for mass selection, (C) 1998 Published by Elsevier Science B.V.