title: Large ontogenetic declines in intra-crown leaf area index in two temperate deciduous tree species.
abstract: The widespread occurrence of age-related changes in leaf morphology and allocation suggests that the leaf area index of individual trees (intra-crown LAI) may decline late in ontogeny. We used direct, within-canopy measurements to quantify the LAI of canopy trees with exposed crowns of two temperate deciduous species. Intra-crown LAI declined from approximately 7 to 4 in Acer saccharum, and from approximately 9.5 to 6.5 in Betula alleghaniensis, as tree size increased (from 15 to 72 cm diameter at breast height [dbh]). For A. saccharum, age (which varied from 30 to 160 years) was a significantly better predictor of LAI decline than dbh. We also modeled the effect of ontogenetic declines in LAI on understory light availability and found that light transmission increases significantly as canopy trees grow and mature. Our results thus suggest that gradual declines in LAI with tree age may play an important and overlooked role in contributing to the heterogeneity of sub-canopy light regimes in mature forests.
authors.affiliation: Faculty of Forestry, University of Toronto, 33 Willcocks Street, Toronto, Ontario M5S3B3, Canada. charles.nock@boku.ac.at
authors.forename: C A
authors.initials: CA
authors.lastname: Nock
authors.forename: J P
authors.initials: JP
authors.lastname: Caspersen
authors.forename: S C
authors.initials: SC
authors.lastname: Thomas
mesh_terms: D031002:Acer / Q000033:anatomy & histology / Q000502:physiology; D000222:Adaptation, Physiological; D029662:Betula / Q000033:anatomy & histology / Q000502:physiology; D018533:Biomass; D018515:Plant Leaves / Q000502:physiology*; D018521:Plant Physiological Phenomena; D013045:Species Specificity; D013472:Sunlight; D013997:Time Factors; D014197:Trees / Q000033:anatomy & histology* / Q000502:physiology*