Preliminary Results of Sugar Maple Carbohydrate and Growth Response under Vacuum and Gravity Sap Extraction

Recent technological advancements have increased the amount of sugar-enriched sap that can be extracted from sugar maple (Acer saccharum). This pilot study quantified overall sugar removal and the impacts of vacuum (60 cm Hg) and gravity sap extraction on residual nonstructural carbohydrate (NSC) concentrations and on stem and twig growth. Vacuum sap extraction (VSE) resulted in significantly greater mean sugar removal (1.19 ± 0.46 kg [SE]) than gravity sap extraction (GSE) (0.48 ± 0.14 kg). Residual stem NSC displayed a pattern of increased concentration with increased extraction. Twig residual NSC concentrations were highly variable, perhaps because of the highly dynamic late spring period, and no clear patterns were observed. Mean radial stem growth in the year after sap extraction was greater in untapped trees (2.93 ± 0.58 mm) than with VSE (1.99 ± 0.44 mm) or GSE (1.67 ± 0.12 mm). The results raise the possibility that sap removal shifts sugar maple NSC source-sink relationships toward storage at the expense of growth.