Understory restoration in a watershed degraded by deer browsing and fern invasion

Browsing by dense (\u3e3–6 deer/km2) populations of white-tailed deer (Odocoileus virginianus) removes tree seedlings from the forest understory, making it difficult for the forest to regenerate if the overstory is damaged or removed. Hay-scented fern can invade the forest understory where deer have damaged and removed other plants. These ferns form dense (90–100 fronds/m2) colonies that cover the forest floor with a thick root mat and form a canopy 60–80cm tall. The ferns interfere with seedling growth, even if deer populations are reduced, because they limit germination sites and block light from reaching the forest floor. This research, conducted in the Quabbin Reservoir Watershed Forest, consisted of four studies that proposed to explain the current distribution of fern colonies, identify specific ways in which past deer browsing and current fern growth affected the germination and growth of several common local tree and shrub species, and evaluate mechanical treatments for hay-scented fern control. By sampling pine plantations thinned at various times over a 30 year period, it was determined that overstory thinning followed by a period of at least 15 years of excessive browsing was required for fern colonies to grow so that understory tree seedling regeneration was blocked throughout a forest stand. Rubus is able to grow through hay-scented fern and expand at the expense of fern colonies. A study of the soil seed bank determined that heavy deer browsing may be associated with depletion of Rubus spp. seeds in the soil. This may slow the recovery process. A study of seedling growth and phenology indicated that seedlings that grow above the fern canopy, Rubus, black birch and white pine, begin photosynthesis early in the spring before annual fern growth blocks the light to the forest floor. In the last study, it was found that while the root mat reduces germination, it does not stop seedling growth to the extent that the intact fern canopy does. Rubus, black birch, and white pine were able to germinate and grew well even with the root mat intact. Breaking up the root mat without removing it increased fern growth in the next growing season