|Niinemets, Ü: Changes in foliage distribution with tree size and relative irradiance: differences between the saplings of Acer platanoides and Quercus robur, Ecological Research, 11, 269-281 (1996)|
Dependencies of foliage arrangement and structure on relative irradiance and total height (TH) were studied in saplings of Acer platanoides and Quercus robur. The distribution of relative foliar area and dry weight (leaf area and weight in a crown layer per total tree leaf area and weight, respectively) were examined with respect to relative height (RH, height in the crown per TH) and characterized by the Weibull function. The distributions of relative area and weight were nearly identical, and the differences between them were attributable to a systematic decline in leaf dry weight per area with increasing crown depth. Foliage distribution was similarly altered by tree size in both species; RH at foliage maximum was lower and relative canopy size (RCS, length of live crown per TH) greater in taller trees. However, the distribution was more uniform in A. platanoides than in Q. robur. Apart from the size effects, relative irradiance also influenced canopy structure; RCS increased in Q. platanoides and decreased in Q. robur with increasing irradiance. As crown architecture was modified by irradiance, foliage distribution was shifted upwards with decreasing irradiance in A. platanoides, but it was independent of irradiance in Q. robur. Higher foliage maximum at lower irradiance in more shade-tolerant A. platanoides is likely to contribute towards more efficient foliar display for light interception and increase the competitive ability of this species in light-limited environments. Consequently, these differences in crown architecture and foliage distribution may partly explain the superior behavior of A. platanoides in understory.