TAMM review: On the importance of tap and tree characteristics in maple sugaring

Abstract

Maple sugaring mainly uses sugar and red maples (Acer saccharum and Acer rubrum) by tapping them for sap in the leafless-state across large portions of their ranges. How much sap exudes from a tap hole and how sweet this sap is, can vary substantially. Year-to-year variation in sap yield and sugar content can be primarily traced to differences in meteorological conditions that drive sap runs. Yet, how much of the total variation in sap yield and sugar content is linked to the year, site, species, tree, or tap has not been investigated systematically.Here, we reviewed the literature and also compiled a dataset of sap yield and sugar content from gravity taps on 324 red and sugar maples. The compiled data originates from multiple studies at ten sites across a large proportion of the ranges of sugar and red maple and stretches over eleven years. Using about 15000 data points on sap yield and sap sugar content, we analysed the importance of tap and tree characteristics, such as height of the tap hole on the stem or diameter at breast height. We also review previous research on the importance of tap and tree characteristics in maple sugaring. Moreover, we partition variability in the data to attribute it to species, site, tree, year, and tap characteristics.Our results indicate that species, site and tree characteristics are the three largest sources of variability with regards to sap yield and the sap’s sucrose concentration. However, differences between years and tap characteristics, which were found to be comparatively minor sources of variability in sap yield and the sap’s sucrose concentration, have attracted far more attention in the past. We advocate for the continuation and expansion of systematic measurements of sap characteristics across a network of sites to further improve our understanding of maple sugaring. Such an understanding will be instrumental to prepare maple sugaring operations against the imminent effects of the climate and biodiversity crises and ensure their sustainability to perpetuate this traditional activity.