Light passage through leaf litter: variation among northern hardwood trees

• Published in: Agricultural and forest meteorology 1999-10, Vol.97 (2), p.103-111
• Main Authors: Schimpf, David J., Danz, Nicholas P.
• Format: Article
• Language: English
• Subjects: Deciduous forest; Leaf; Light penetration; PAR; Transmissivity
• ISSN: 0168-1923; 1873-2240
• DOI: 10.1016/S0168-1923(99)00064-7

Leaf litter may influence the environment for germination and photosynthesis of seedlings and other small plants through its effects on transmitted light. We measured red : far-red ratios (R/FR) and photosynthetically active radiation (PAR) transmitted through individual dead leaves from 10 species of deciduous trees of the northern hardwood region of eastern North America. The leaves were collected from the forest litter between spring snowmelt and canopy budbreak, when irradiances on the forest floor are highest. Mean transmittance of PAR varied among species from about 0.5 to 20% for dry leaves and from about 2 to 38% for wet leaves. Transmittance of PAR was greatest for dead leaves from shade-tolerant late-successional species, least for those from shade-intolerant early-successional species, and intermediate for those from moderately shade-tolerant species. Shade leaves transmitted more PAR than sun leaves of the same species, significantly so for Quercus rubra, Acer saccharum, and Fagus grandifolia. Transmitted R/FR was greater for late-successional species than for early-successional species, especially for shade leaves. These ratios tended to be higher for wet leaves than for dry leaves. Shade leaves tended to have higher ratios of transmitted R/FR than sun leaves of the same species, significantly so for Q. rubra, A. saccharum, and F. grandifolia. Changes in both canopy species composition and the proportion of shade leaves during succession in these forests should bring about concomitant environmental trends toward greater favorability for the germination of seeds or spores needing high R/FR, as well as for photosynthesis by plants that are short enough to be covered by leaf litter.