Light Beneath the Litter in a Tropical Forest: Effect on Seed Germination

The spectral composition of the light transmitted through the forest canopy, through dry and moist litter leaves, and through intact forest litter was measured in a tropical rain forest in Mexico. Germination of photoblastic seeds of some pioneer trees and shrubs was studied over a light quality gradient, and in field germination experiments on the surface of the forest floor and beneath the litter layer. There is a shift to longer wavelengths inside the forest that is even greater beneath the litter. Light filtered through dead leaves strongly inhibits germination as demonstrated with field and laboratory germination experiments. The role of litter as a light filter might be important in maintaining a reserve of dormant seeds in the soil in tropical rain forests.