Effects of Shading and Fertilization on Resistance of Winter‐Dormant Birch (Betula Pendula) to Voles and Hares

Seedling representing four families of European white birch (Betula pendula) were grown through their first growing season in two fertilization and three shading treatments. The growth responses of seedlings were measured, and after complete winter hardening the basal parts of seedlings were offered to voles (Microtus agrestis) and the top parts of the same seedlings were fed to hares (Lepus timidus). The growth response of 1—yr—old birch seedlings to fertilization and shading was family specific. Nitrogen fertilization generally increased the biomass accretion and the palatability of the seedlings to voles. Fertilization significantly decreased resistance of seedlings to hares in only one out of the four birch families. Shading decreased the biomass accretion of seedlings and increased their palatability to hares but tended to decrease the palatability to voles. The differing preferences of the two mammalian herbivores for seedlings grown under different environmental conditions may be due to vertical differences in the defense of birch seedlings to herbivore feeding. No trade—off was found between seedling defense and growth.