Decreased radial growth in sugar maple trees tapped for maple syrup

The conversion of sap from sugar maple (Acer saccharum) to syrup is a multi-million dollar agroforestry industry in North America. Sugar maple trees take decades to reach a size that can be tapped; therefore, maintaining vigorous trees is crucial to the industry's sustainability. Our objectives were to identify whether syrup production altered radial growth or cambium miner activity. We extracted increment cores and measured ring widths from trees tapped for syrup production and untapped reference trees. In Pennsylvania and Ontario, radial growth in tapped trees was significantly reduced compared to reference trees. In New York, there was no significant difference in radial growth between tapped and reference trees. All sites showed a significant reduction in radial growth following commencement of tapping, compared to growth rates prior to tapping. This pattern was not identified in reference trees, which indicates that it was not an artifact of age-related growth trends. There was no significant difference between cambium miner activity in tapped and reference trees. We concluded that the reduction in sugar maple radial growth is likely due to reallocation of resources as the tree heals the damage to the stem during tapping.