DIFFERENCES IN NUTRITIONAL QUALITY BETWEEN HERBACEOUS PLANTS AND BARK OF CONIFERS AS WINTER FOOD FOR THE VOLE MICROTUS-PENNSYLVANICUS

1. Meadow voles (Microtus pennsylvanicus) are known to inflict severe winter damage on young tree plantations by gnawing the bark. This is often attributed to a lack of quality and quantity of food supply, although no direct evidence has ever been found. A first step in this direction was initiated by comparing the quality of food supply between herbaceous plants and bark of coniferous species during the winter periods of 1987-88 and 1988-89. 2. Food quality was assessed by measuring the content of protein, total nonstructural carbohydrates (TNC) and total phenolics using standard methods. 3. The nutritional value of herbaceous plants was overall much greater than that of the bark of conifers for both winters analysed. Ratios involving protein/phenolics and TNC/phenolics were up to 50 times higher in herbaceous species than bark of conifers. 4. Nutritional components from herbaceous plants did not vary much between winter months unlike the bark tissues of conifers. 5. These results indicate that voles do not attack conifers because of their high nutritional quality suggesting that other factors such as a lack of a good quality alternative food supply (herbaceous plants) are involved.