PARENT SESSION
Oral Session #57: Plant Competition I.
Presiding: T. Seastedt
Wednesday, August 7. 8:00 AM to 11:30 AM. Grand Ballroom Central, Radisson.
Resource availability and tree seedling performance along natural gradients of understory shrub density in an eastern deciduous forest.
Beier, Colin*,1, Nilsen, Erik1, Horton, Jonathan1, Walker, John1, Clinton, Barton2, 1 Virginia Polytechnic Institute and State University, Blacksburg, VA2 USDA Forest Service Southern Research Station, Otto, NC
ABSTRACT- Inhibition of canopy tree recruitment beneath thickets of Rhododendron maximum L. (Ericaceae) has long been observed in S. Appalachian forests, yet the mechanisms of this process remain unresolved. In this study, we examined relationships between the densities of two thicket forming subcanopy shrubs (R. maximum and Kalmia latifolia L.), resource availability, herbivory rates and seedling performance and survivorship. We planted oak seedlings in forest plots randomly located along gradients of shrub density at two contrasting sites in the Coweeta Basin, NC, and measured seedling response (growth, biomass) to resource availability. Seedling phenology, health (i.e. damage from herbivory) and survivorship were measured biweekly during the growing season. We found that numerous shrub-mediated factors interacted to influence seedling performance, particularly light attenuation, nitrogen availability and leaf herbivory. Seedling biomass, open-canopy light availability and litter %N were negatively correlated with R. maximum; while seedling mortality rates, soil metals (Cu,Fe,Al) and early-season herbivory rates were positively correlated with R. maximum density. Seedling leaf area and growth was positively correlated with light and litter %N, while negatively correlated with soil [Al] (an indicator of acidic, nutrient poor soils at both sites). K. latifolia had relatively little influence on resources, seedling performance or herbivory rates. In contrast to previous studies which have emphasized light attenuation as the primary mechanism by which R. maximum inhibits recruitment, this study indicates that belowground resource deficiencies and herbivore damage are also important factors.
KEY WORDS: Rhododendron maximum, competitive interference, canopy tree recruitment, seedling herbivory