Large Ontogenetic Declines in Intra-crown Leaf Area Index in Two Temperate Deciduous Tree Species

• Published in: Ecology (Durham) 2008-03, Vol.89 (3), p.744-753
• Main Authors: Nock, C. A., Caspersen, J. P., Thomas, S. C.
• Format: Article
• Language: English
• Subjects: Acer - anatomy & histology; Acer - physiology; Acer saccharum; Adaptation, Physiological; allometry; Animal and plant ecology; Animal, plant and microbial ecology; Betula - anatomy & histology; Betula - physiology; Betula alleghaniensis; Biological and medical sciences; Biomass; Branches; canopy dynamics; canopy gaps; Concepts & Synthesis: Emphasizing New Ideas to Stimulate Research in Ecology; crown structure; deciduous forests; Demecology; Ecology; Forest canopy; Forest ecology; forest trees; Fundamental and applied biological sciences. Psychology; gap dynamics; General aspects; Genetics; leaf angle; Leaf area; Leaf area index; Leaves; light; light transmission; ontogeny; Plant ecology; Plant growth; Plant Leaves - physiology; Plant Physiological Phenomena; Plants and fungi; prediction; Saccharum; simulation models; Species Specificity; Sunlight; temperate forests; Time Factors; Tree age; tree and stand measurements; tree crown; Tree crowns; tree growth; tree ontogeny; Trees; Trees - anatomy & histology; Trees - physiology; understory
• ISSN: 0012-9658; 1939-9170
• DOI: 10.1890/07-0531.1

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 ∼7 to 4 in Acer saccharum, and from ∼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.