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A stand of pine trees.

Understanding Tree Structure

Authored by:

How trees stand and fall is centered upon the load they are under and how they hold against wind and gravity. Understanding tree structure, and how it bends and twists in the wind, is key to effective risk management along streets, in parks, and across landscapes. A publication supporting this subject matter is: “Standing Against The Wind: Introduction To Tree Structural Mechanics.” Warnell School of Forestry & Natural Resources Outreach Publication WSFNR-22-65A, available on the Warnell Outreach Publication website.

This publication is a brief introduction to a variety of tree biomechanical and failure mechanisms, concentrating almost exclusively upon above-ground tree structure. Tree root anchorage and strength, and associated soil strength issues, are covered elsewhere in other outreach publications.

A triangle with the words "wind load impacts" in the center. The words "stem height" are shown in red on the upper right hand corner of the triangle. The words "branch mass" are displayed in green on the upper left corner of the triangle, while the words "stem/root base" is written in blue across the bottom of the triangle.
Three structural components of a tree model which interact with wind loads, and which are optimized by continued growth or shedding to maintain a tree upright.

Trees deal with an environment full of constraints. Many of these constraints involve shortages of essential resources, most crucially light and water. Other constraints deal with social interactions and interference (competition/allelopathy) with other living things. To be successful in life, trees are always optimizing their biology for surviving, thriving, and reproducing. One critical component of a tree’s biological success and sustainability is generating a viable structure to display, contain, and support its biology while interacting with its environment.

Trees exist within a mechanical load environment where they must defend their position to live by bolstering and continually reinforcing their structure, or by reorienting structures to a reduced stress/strain position. The environment challenges a tree with many biological and structural constraints, and a tree responds using energy and resources to successfully colonize, control, and defend resource-containing, ecologically viable space. Tree structure must continue to develop in response to environmental loads in order for trees to be successful. This publication helps tree owners and tree health care providers better care for trees.


Professor of Tree Biology & Health Care, University Hill Fellow for Distinguished Public Service & Outreach

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