PARENT SESSION
Poster Session #29: Plant Ecology: Environmental controls.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Trends in light adaptations of forest herbs on a productivity gradient.

Adkison, Greg^*,1, Gleeson, Scott¹, ¹ University of Kentucky, Lexington, KY

ABSTRACT- Whether species distributions are controlled by many factors and traits or just a few is a fundamental question in ecology. The theory of limiting traits predicts that at the community level, the mean value of traits that limit fitness will change as the optimal value of the trait changes, and the most intensely limiting traits will exhibit the lowest phenotypic variation. These predictions were evaluated in a diverse understory herb community of an eastern deciduous forest. The primary gradient in this system is complex with an increase in diversity and biomass corresponding to higher moisture and soil nutrients. Light declines along the gradient as the tree canopy thickens, suggesting a pronounced increase in relative light limitation with increased productivity. Four traits--leaf size, SLA, etiolation and leaf:shoot mass (LSR)--were measured on every plant found within 60, 0.25m² quadrats that were randomly placed along a transect spanning the gradient. Averaging over plants within quadrats, each trait increased along the gradient except LSR which declined. These results were consistent with predicted changes in optima across the gradient. Contrary to expectation, there was no significant trend in variability (CV) for any trait along the gradient. Leaf size was more variable within quadrats than the other traits, consistent with more intense selection on LSR, etiolation, and SLA relative to leaf size.

KEY WORDS: species distributions, fitness, limiting traits