NUTRTIONAL QUALITY OF GLYPHOSATE-INJURED BROWSE FOR MOOSE IN MAINE

Abstract

Live deciduous vegetation on regenerating clearcuts previously treated with the herbicide glyphosate frequently exhibits evidence of injury, which may affect the nutritional value of this vegetation for browsing herbivores such as moose. We compared the nutritional quality of glyphosate-injured and uninjured twigs (current annual growth) from red maple (Acer rubrum) and white birch (Betula papyrifera), two abundant and commonly used winter foods of moose in Maine, at 17 months posttreatment. For red maple, neutral and acid detergent fiber (NDF and ADF) concentrations were 18% less (P < 0.001), and lignin-cutin was 8% greater in injured than uninjured twigs. Predicted digestible dry matter (DDM) and digestible energy (DE) values were 7% greater (P = 0.003-0.014) in injured than uninjured twigs. Crude protein concentrations were low in red maple overall, but were greater (P < 0.001) in injured than uninjured twigs. In contrast, for paper birch, NDF and ADF concentrations were 6 and 8% greater (P = 0.002-0.011) and DDM and DE values were 8-11% less (P = 0.001-0.014) in injured than uninjured twigs. Lignin-cutin concentration was greater in injured than uninjured twigs. Crude protein content was not affected by injury (P = 0.97) in paper birch. Differences in the nature and magnitude of effects on nutritional quality for these two browse species demonstrates that there is not a generalized response to glyphosate injury. While measurable effects on nutritional quality of browse exist, absolute differences were generally small and may not represent important effects on diet quality of moose.