Sources of temporal variation in sap sugar content in a mature sugar maple ( Acer saccharum) plantation

Abstract

Temporal factors affecting sap sugar content (SSC) were assessed in a 65-yr-old plantation of sugar maple ( Acer saccharum Marsh.) located in Québec. 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 tree variation in SSC was extensive, ranging from 1.3 to 5.5% for spring 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 extensively between sampling hours within days, while it varied significantly among sampling days for both years analysed. However, the largest source of variation in SSC was between the 2 sampling years. Tree relative performances in SSC were moderately conserved among days within years and to a lesser degree, between sampling years. The relative magnitude of the differences between statistical treatments and the stability analysis of tree relative performances indicated that, for adequate estimation of an individual tree's SSC, sampling over years appears superior to sampling over several days within a single sugar season. Also, sampling towards the end of the sugar season or during days with lower SSC appears less reliable for mass selection.