PARENT SESSION
Poster Session # 14: Forest Ecology.
Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Establishing the tree regeneration template: The role of the understory layer and herbivory on seedling dynamics.
Royo, Alejandro*,1, 2, Carson, Walter1, 1 University of Pittsburgh, Pittsburgh, Pennsylvania, USA2 USDA Forest Service, Northeastern Research Station, Warren, Pennsylvania, USA
ABSTRACT- Competition from hay-scented fern (Dennstaedtia punctilobula) and excessive white-tailed deer (Odocoileus virginianus) browsing severely limit tree recruitment throughout large portions of northeastern forests. Their combined effect threatens to reduce understory tree species composition to species that are both shade-tolerant and browse-resistant, thus altering the regeneration patterns that occur following overstory gap formation. If competition by the fern layer and deer herbivory regulate tree seedling establishment and diversity, we predict that gap creation in the fern canopy will increase the recruitment, survival, and growth of less shade-tolerant species in a manner comparable to overstory gap dynamics. Furthermore, we predict deer exclusion will increase recruitment, survival, and growth of browse-intolerant or preferred tree species. We are testing these predictions using a factorial field manipulation of deer herbivory using exclosures and hay-scented fern cover via the creation of six different gap sizes. Currently, we are monitoring the growth and survival of over 30,000 marked seedlings at three sites within the Allegheny National Forest, Pennsylvania. Our initial census confirmed that the seedling layer at these sites is dominated (>94%) by black cherry. However, by the second year fern gaps stimulated germination of several species including birch, pin cherry, red maple, and white ash, but not black cherry. Woody species richness increased under fern gaps relative to controls (P<0.001). Fern gaps significantly increased survival (P<0.001) and marginally increased growth (P=0.059) of black cherry seedlings. In contrast, deer exclusion did not affect richness, survival, or growth for this small (< 20 cm) seedling size class. The data suggest that fern and deer impacts do not operate concurrently. Initial control of seedling layer is strongly limited by a dense fern understory and deer may only exert control on the ensuing larger seedling size classes.
Key words: Odocoileus virginianus, understory, Dennstaedtia punctilobula, tree-seedling