Structural and Functional Features of Mesophytic Forests in the East-Central United States

Abstract

Structural characteristics and functional properties of trees are used to investigate regional-scale variation in forest structure in mesophytic forests of the southeastern United States. Compositional data for 112 sites from Braun (1950) are recast into numerical expressions of structural features (e.g., leaf form, bark thickness, and seed weight) and functional traits (e.g., shade tolerance, dispersal agency, and windfirmness) of forests. These data are analyzed by principal components analysis to arrange sites on the basis of structural similarity and to interpret links between forest structure and environmental gradients of available moisture, soil fertility, and disturbance regime. Principal components analysis generates a triangular array of stands, with hemlock/spruce sites, hardwood coves, and dry upland forests at the vertices. Hardwood coves on mesic, fertile substrates are associated with small, simple leaves, gravity seed dispersal, and a high degree of windfirmness. Hemlock/spruce sites on mesic. infertile substrates exhibit short needles, light weight, wind-dispersed seeds, and a low degree of windfirmness. Dry upland forests exhibit thick barks, stout twigs, intolerance of shaded conditions, and seed dispersal by small mammals. These suites of structural/functional traits are interpreted to represent collective responses of plant cover to site factors (moisture/nutrient availability) and disturbance regimes associated with each forest type.

Key Words:

• structural/functional analysis
• vegetation/environment relationships
• mesophytic forests
• southeastern United States
• available moisture
• soil fertility
• disturbance regime