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

The effects of light and soil fertility on seedling survival and growth in a dry tropical forest.

IYER, MEERA^*,1, KOBE, RICHARD¹, ¹ Michigan State University, East Lansing, Michigan

ABSTRACT- The effects of light and soil nutrients on species dynamics in dry tropical forests are poorly understood. To investigate their role, we transplanted seedlings of Astronium graveolens, Bombacopsis quinata, Cordia gerascanthus, Dalbergia retusa and Tabebuia rosea into 366 plots stratified across gradients of light and soil phosphorus availability in Palo Verde National Park, Costa Rica. Half of the plots were fertilized at the rate of 100 kg/ha using phosphate rock. However, subsequent analyses revealed no significant differences between control and fertilized plots in phosphorus availability which ranged from <1 to ~150 mg P/kg soil. Light availability, measured with hemispherical canopy photographs, varied from ~4% to ~40% full sun. Seedling growth and survival were monitored over two growing seasons. Survival and relative growth of only Dalbergia increased with increasing phosphorus availability. All species except Astronium showed increased relative growth and survival with increased light availability. Across species, relative growth at high light strongly correlated with relative growth at low light but we did not find a trade-off between high-light growth and low-light survival. However, based on their survival and growth under different light availability, we assigned performance ranks for each species. Under low light conditions, Cordia performs best, under intermediate light levels, Tabebuia is the competitive dominant, while Dalbergia has the highest performance rank under high light availability.

KEY WORDS: dry tropical forest, soil phosphorus