Sap Yield and Sugar Content of Boxelder and Norway Maple Trees in Northern Utah

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Sap Yield and Sugar Content of Boxelder and Norway Maple Trees in Northern Utah Jesse Mathews1, Youping Sun1, Paul Harris1, Xin Dai2, Steven Price3, Darren McAvoy4, Michael Farrell1, and Kelly Kopp1 KEYWORDS. Acer negundo, Acer platanoides, maple sap, maple syrup, air temperature ABSTRACT. Maple syrup is a well-known natural sweetener made from the sap harvested from maple trees (Acer sp.). The North American scientific literature regarding maple syrup has predominantly originated in the Northeastern United States and Canada. However, the range of this Holarctic genus extends across the continent and all species produce sap with the potential for syrup production. This study focuses on two maple species commonly found in Northern Utah, namely the native boxelder (Acer negundo) and the introduced Norway maple (Acer platanoides). Thirty trees of each species were tapped in Cache Valley, UT, USA, on 19 Feb 2022, and measured for daily sap yield and sugar content until the season ended 37 days later on 27 Mar 2022. The same trees were re-tapped on 1 Mar 2023 and taps were removed 41 days later on 10 Apr 2023. Average 2022 sap yields were 22.1 L for boxelder and 7.5 L for Norway maple per tree. In 2023, average sap yields were 26.4 L for boxelder and 9.3 L for Norway maple per tree. Boxelder trees produced an average sap yield more than double that of Norway maple in both years. Sugar content was similar for both species ranging from 2.2% to 2.8%. Air temperatures were analyzed using data from Utah AgWeather System weather stations nearest to the trees, and air temperature had a significant impact on sap yield. It was found that an average daily air temperature of 0.5 C and a daily air temperature difference of ~10 C with a minimum air temperature close to 25 C and a maximum air temperature of ~6 C was the optimal condition for production. An analysis of the mineral nutrient concentrations in the sap and soil showed no correlation. These findings indicate that there is potential for using Utah’s maple species for syrup production.

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aple syrup is a popular agricultural commodity produced mainly in Quebec, Canada, and the northeastern United States. Quebec itself accounts for more than 90% of maple syrup production in Canada and 75% of production worldwide, with most of the remaining 25% being produced in the United States [Crops and Horticulture and Division Agriculture and Agri-Food Canada (CHDAAFC) 2021]. Within the United States, Vermont produced 40% of the country’s maple syrup in 2021, and other top-producing states that year include Maine (14%), New York (17%), Pennsylvania (5%), and Wisconsin (10%) [US Department of Agriculture (USDA), National Agricultural Statistics Service (NASS) 2022]. Sugar maple (Acer saccharum) is the most popular species to tap in these areas because of its higher sugar content (Perkins et al. 2022). Sugar maple does not survive well in Utah, in part because of to higher soil pH compared with its 52

native range (Boettinger 2009). Sugar maples also struggle in excessively dry soils, which occur frequently in Utah (Boettinger 2009; Perkins et al. 2022). Many maples (Acer sp.) have problems with iron chlorosis in soils with a pH over 7.0, which makes it hard to uptake iron (Kuhns and Koenig 2002). This might be one contributing factor to the lack of historical maple syrup production and cultural familiarity with production in Utah. About 211,714 boxelder (Acer negundo) trees exist in the state that could be tapped (USDA, Forest Service 2022). Similar inventory estimates are not available for Norway maple (Acer platanoides), as they grow primarily in urban settings, but they are widespread and common in both parks and domestic landscapes in Utah. Little information has been published about the sap yield and quality of these maple species in the state. Although tree characteristics can influence annual sap yield, climate conditions, mostly revolving around air temperature during the sap flow season,

have long been identified as the main factor affecting annual changes in maple sap yields (Duchesne and Houle 2014; Duchesne et al. 2009; Kim and Leech 1985). Sap exudation occurs when winter temperatures fall below freezing at night and rise above freezing during the day, which causes freeze-thaw cycles, creates positive pressure inside the tree, and forces sap out through tap holes because of the lower atmospheric pressure outside the tree (Perkins et al. 2022; Stockie et al. 2022; Tyree 1984). Late winter weather conditions are monitored for daytime air temperatures above freezing that initiate the freezethaw cycle. In addition, observations are often made on a few trees tapped early to monitor sap flow initiation indicating when the remaining trees should be tapped, thereby, beginning the tapping season. As the season progresses toward spring, sap flows either become minimal or the tree begins to break dormancy leading to “buddy” sap with poor quality because of its off-tasting flavor (Camara et al. 2019). Because of the annual variability of seasonal air temperatures, the production season length, number of days of sap flow and collection, and timing can be inconsistent across years, often lasting only 4 to 6 weeks (Giesting 2020). Optimal sap production areas are found at latitudes 43 N, with latitudes within a few degrees above and below having comparable sap yields (Rapp et al. 2019). Northern Utah, generally considered all areas of the state from the Salt Lake area and north, is at a latitude close to 41 degrees north, which falls within the high sap production range. Utah receives less than 33% of the annual precipitation of the high syrup production states mentioned previously [US Department of Commerce, National Oceanic and Atmospheric Administration (NOAA) 2023], and soil moisture has been shown to affect sap yield (Perkins et al. 2022). It also has large areas of either thinly diffused forests or no forest at all, contrasting with densely diffused forests in the northeastern United States (USDA, Forest Service 2023). As mentioned previously, sugar maples do not grow well in Utah, in part because of the differences in soil in the state as compared with soil in the northeastern United States. This is significant because it is known that soil composition does influence sap composition

February 2024 34(1)


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