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Harvard Forest Symposium Abstract 2017

  • Title: Climate effects on maple sap quantity and quality: the Acer Climate and Socio-Ecological Research Network (ACERnet)
  • Primary Author: Joshua Rapp (Harvard Forest)
  • Additional Authors: Selena Ahmed (Montana State University); Boris Dufour (University of Quebec at Chicoutimi); Ryan Huish (University of Virginia); David Lutz (Dartmouth College); Toni Lyn Morelli (University of Massachusetts - Amherst ); Kristina Stinson (University of Massachusetts - Amherst )
  • Abstract:

    The Acer Climate and Socio-Ecological Research Network (ACERnet) is an international consortium of scientists studying climate impacts on sugar maple and maple syrup production. Our research focuses on the relationship between sap quality and climate; we collect data on sap quantity and quality across the range of sugar maple, from southern Virginia to northern Quebec, and Massachusetts to Indiana. ACERnet formed in 2014, when collaborators in Virginia, New Hampshire and Quebec, and began collecting sap data following protocols developed at Harvard Forest (Rapp has collected sap flow and sugar content data at Harvard Forest since 2012). We also began collecting samples to examine sap secondary chemistry at these four sites in 2014. In 2016 we added an additional site in southwestern Virginia and another in Indiana. Since 2015 we have collected sap from red maple trees as well, at the sites where they are present.
    At each site in the network, we tap trees during the tapping season (late-winter) following tapping guidelines from the North American Maple Syrup Producers Manual. Trees >12” DBH (diameter at breast height) and < 20” DBH get one tap, while trees > 20” DBH get two 5/16” taps. Sap is collected on every day most trees have some sap flow (> 1 L sap in bags). We weigh the sap in the sap sak (or bucket) using a hanging balance and measure sap sugar content using a refractometer. Three times per season we collect sap in 50 mL centrifuge tubes for chemical analysis (primarily phenolics). We also collect sap for secondary chemistry analysis from 5 sugar maple and 5 red maple trees each day of sap collection. For analysis of the influence of daily weather on sap quantity and quality, we use local weather station data (from the Fisher Meteorological Station at Harvard Forest). For network-wide climate analysis we use Daymet gridded climate data.
    ACERnet spans a wide range of climates; mean annual temperature ranges from 2.5C at the northern-most site in Quebec to 12C in southwest Virginia. The sap collection season correspondingly varies from January to early March in VA to April to May in Quebec. The longest and most variable seasons tend to be in the central part of the gradient. Harvard Forest is a good example of this; in 2015 The season ran from mid-March to mid-April, while in 2012 and 2016 the season ran from early to mid-February to mid-March. Total sap flow tends to be higher in earlier seasons across the network. Preliminary analysis indicates that total season sap flow is related to the strength of the freeze thaw cycle, and especially the freeze part of the cycle; sap flow is correlated with the cumulative degrees below freezing during the sap season. Sap sugar content is variable among sites and years. Total phenolic content of the sap was higher in VA than MA or NH in 2014.

  • Research Category: Regional Studies, International Research Projects, Conservation and Management