PARENT SESSION
Oral Session # 79: Forest Ecology V: Structure; Dispersal; Competition.
Presiding: J Schnurr
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 104.

Predicting seed/seedling dynamics: The non-Tarot card approach.

Cosgriff, Robert^*,1, ¹ Great Rivers Field Station, Brighton, IL, USA

ABSTRACT- A seed/seedling dynamics study was conducted from 1996-2001 on five key pools of the Upper Mississippi River System (UMRS). Twenty-four species were identified on the five pools in which Populus deltoides, Betula nigra, Acer saccharinum, Fraxinus pennsylvanica, Ulmus americana, and Acer negundo were the most common species encountered. River pool, forest community, species, and month were significant predictors of seed density. Year was not a significant predictor of seed density. River pool and germination year were significant predictors of seedling density, whereas forest community, germination month, and species were not. Although B. nigra produced the greatest number of seeds and had high reproductive power, this species had poor representation in the seedling cohorts of the sites studied (germination ranged from 0.0-0.15%). Likewise, P. deltoides had no seedling germination in any of the sites studied. The percent germination of A. saccharinum varied from 0.35% in the wet forests of the La Grange Pool to 218.2% in the wet forests of Pool 13. Fraxinus pennsylvanica and U. americana seed germination ranged from 0.0-25.3% and 0.92-85.0%, respectively. Hard-mast species (Quercus and Carya spp.) had much lower germination rates than what was expected (0.0-25.3%). Due to low numbers of seedlings in all but five species, survivorship analysis was conducted for F. pennsylvanica, A. saccharinum, U. americana, Rhamnus cathartica, and Zanthoxylum americanum. Seedling survival was strongly related to species, river reach, and day of mortality. Fraxinus pennsylvanica, Z. americanum, and U. americana had greater long-term survivorship than did A. saccharinum and R. cathartica. Survivorship within a species also varied according to forest community. Fraxinus pennsylvanica had a greater chance of surviving on dry forests than wet (Chi-square=32.74, df=1, p<0.001) whereas A. saccharinum had a greater chance of survivorship on wet forests (Chi-square=41.76, df=1, p<0.0001). All river reaches other than Reach 4 and the La Grange Reach showed significant differences in seedling survivorship curves. Likewise, there were significant differences in survival curves between forest communities. Dry forests had greater seedling survivorship than wet forests.

Key words: seed/seedling dynamics, floodplain forest, Upper Mississippi River System