PARENT SESSION
Poster Session 37: Forest Ecology.
Thursday, August 5 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.
Rooting of prostrate stems: A life-history trait in suppressed Acer saccharum seedlings.
Woods, Kerry 1, 1 Natural Sciences, Bennington, VT, 05201
ABSTRACT- Acer saccharum seedlings in old-growth northern hardwood forests appear to root freely along buried, prostrate portions of stems; some aerial shoots emerge nearly 1 m from original tap-root. This behavior has not been reported for A. saccharum, but may be an adaptive aspect of the life-history of this late-successional canopy dominant (similar behavior have been reported, and life-history consequences explored, for Abies balsamea in boreal forests). Typically, suppressed A. saccharum seedlings form dense understory stands, but seedlings rarely grow taller than ca. 1 m beneath intact canopy, probably due to decreases in shade-tolerance with size (and concomitant changes in ratio of photosynthetic to non-photosynthetic tissues) and, in the northern MI study area, to intensive deer browse. Stem-layering may allow individuals to abandon woody biomass, remain small and shade-tolerant for longer periods, and so increase likelihood of surviving until canopy openings permit rapid growth and canopy recruitment. We aged and took detailed morphological measurements (layered-stem length, aerial shoot length, leaf area, woody biomass, stem dimensions at various points) for ca. 700 seedlings beneath closed canopy in old-growth northern hardwoods in northern MI, USA. Relationships among variables suggest that layered seedlings allocate less resources to woody stem-growth and can support greater leaf area than unlayered seedlings of comparable total stem-length. Nearly all stems more than 10 yr old were layered, but there is some suggestion that layered stems can reach greater ages. Excavation and growth-ring analysis of released saplings in gaps shows that layered seedlings are capable of release and rapid, competitive growth. The ability to layer, in combination with A. saccharum's maintenance of persistent "seedling banks", may be shape the species' demography and contribute to its persistence in late-successional forests.
Key words: shade-tolerance, Acer saccharum, plant life-history