Crown thinning in canopy trees of two temperate deciduous species: Implications for light transmission in tolerant hardwood forests.

摘要

Leaf area index (LAI) often increases with stand age and subsequently declines following canopy closure in monospecific forests. Typically, these declines in stand-level LAI are attributed to population processes that decrease canopy cover, such as tree mortality and crown abrasion. However, recent evidence of age-related changes in allocation and leaf morphology suggest that intra-crown LAI may also decline late in ontogeny. Using vertical line transects, the intra-crown LAI for canopy trees of two temperate deciduous species was directly quantified. Intra-crown LAI declined from 7 to 4 for Acer saccharum and from 9 to 5 for Betula alleghaniensis across the size range (15--72 cm dbh). For A. saccharum , tree age was a better predictor of LAI decline than dbh (range 30--160 y.). These results indicate that ontogenetic declines in intra-crown LAI are underappreciated and may significantly contribute to light transmission in mature forests, potentially influencing tree regeneration.