PARENT SESSION
Oral Session 81: Forest Ecology IV: Seeds, Growth, and Recruitment.
Presiding: J Kush
Wednesday, August 4, 1:30 PM to 5:00 PM, Meeting Room C 120.
Substrate limitation of seedling recruitment in northern hardwood forests.
Caspersen, John1, 1 Faculty of Forestry, Toronto, Ontario, Canada
ABSTRACT- Tree seedling recruitment is limited both by supply of seeds from parent trees and by the availability of suitable substrates for germination. Thus, species which specialize in colonizing less common substrates (i.e. exposed mineral soil, decaying logs) may not regenerate even when abundant in the overstory. Failure to regenerate substrate specialists is a common problem in managed forests, including northern hardwood forests managed under single-tree selection. Various substrate treatments have been proposed as a means to promote recruitment of substrate specialists in northern hardwood forests, but the successful implementation of these methods is limited by a lack of information on the rates of recruitment on different substrates. To address this problem, I have quantified rates of recruitment (# of germinants/m2/year) of the five most common species on six different substrates, while also controlling for variation in the spatial distribution and abundance of parent trees. Germinants of Acer saccharum (by far the most common species) are most abundant on leaf litter, but are also fairly abundant on non-litter substrates, including bare mineral soil and rotten logs. In contrast, the other four species (Betula alleghaniensis, Fagus grandifolia,, Tsuga Canadensis, and Abies balsamifera) are more abundant on the non-litter substrates, particularly bare mineral soil, rotten logs, and moss. For several of these species, seedling abundance on non-litter substrates is ten times greater than seedling abundance on leaf litter. These results suggest that the abundance of the less common species may well be limited by the availability of non-litter substrates. Thus, the estimated recruitment rates should prove valuable in designing substrate treatments to promote the recruitment of substrate specialists.
Key words: substrate limitation, seedling recruitment, northern hardwoods