Control of Shoot / Root Balance in Trees

A critical feature of tree growth regulation involves functionally balancing the top of the tree with the bottom. Concepts of shoot / root ratios and how a tree can maintain a resource balance between apparently competing needs have been proposed and tested for accuracy. Of all the working models examined, one form has proven over the last two decades to serve in describing regulatory partitioning between shoot and root.

The type of model proven to be most effective is called a "Thornley" model, although many derivations and more refined systems exist. The result is a means of understanding tree functions in a holistic sense and predicting resource allocation patterns between shoot and root. Generically, shoot size and function is equated with root size and function. The purpose of the shoot is to utilize soil gathered resources to capture and ship carbon to the root. The purpose of the root is to utilize carbon to capture and ship soil resources to the shoot. Using only a few basic feature of shoot and root can let us estimate the scale and intensity of shoot / root interactions. (Figure 3A)

(This publication is a synthesis of the tree growth regulation and correlation literature. General processes and systems presented here represent educational models which professionals can use to better appreciate and understand basic tree functions. These models do not represent actual physiological mechanisms, but simple theoretical means of explaining tree reactions within the environment.)

(FOR98-003) January 1998

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