Abstract
According to the uniform-stress principle of stem formation, the amount of leaf area a tree carries and the leverage it exerts on the stem determine the stem dimensions. Within an even-aged monoculture, the leaf area per tree and the leverage placed on the stem are functions of tree density and tree height. The uniform-stress principle presents the means to translate density effects on crown characteristics into stem dimensions and total standing volume. This approach is truly a top-down method of simulating growth tree and stand growth because leaf area and other crown properties must be determined before stem size and taper can be calculated. Each crown property influences either the sail area or the leverage placed on the stem, but the degree to which a specific crown property affects these parameters changes with stand density and height. Leverage is the more complicated of the two variables, being a function of the height to the base of the live crown and the vertical distribution of leaf area. The purpose of this brief review is to summarize the effects of stand density on the height to the base of the live tree and the vertical distribution of leaf area and the various ways these variables have been quantified.
Highlights
The relationships between a tree’s crown and stem and taper are often explained in terms of the functional needs of the leaf area
The relationships equate the amount of hydraulic or mechanical support needed by the leaf area into stem dimensions; either function could be the basis of a model to simulate stem growth through time given corresponding changes in leaf area
Forests 2018, 9, 334 knowledge of how tree density and height affect the distributions of leaf area, the biomechanical function creates a method for predicting stem dimensions as a stand moves past canopy closure to the stem-exclusion and self-thinning stages
Summary
The relationships between a tree’s crown and stem and taper are often explained in terms of the functional needs of the leaf area. Forests 2018, 9, 334 knowledge of how tree density and height affect the distributions of leaf area, the biomechanical function creates a method for predicting stem dimensions as a stand moves past canopy closure to the stem-exclusion and self-thinning stages. Dean et al [15] constructed a model based on the biomechanical interaction between the vertical profile of the leaf area of the average crown and the bending stress created by wind drag through the crown. The uniform-stress model is obviously too simple to account for the detailed stem morphology of individual trees in specific situations It is derived from static mechanics, and it describes average stem taper developed over time. The purpose of this report is to briefly review how tree populations and stand development shape the dimensions of the crown and the vertical distribution of foliage within them and to review the equation forms that have been used to relate these various crown characteristics to tree density
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