Stress

“Many of the trees they planted [in Biosphere 2] to create a rain-forest ecosystem grew rapidly but then fell over before reaching maturity. The designers had not realized that young trees need wind to  grow properly. When the wind blows, it bends the tree, which tugs at the roots on the windward side and compresses the wood on the other side. In response, the root system expands to provide a firmer anchor where it is needed, and the compressed wood cells change their structure to become stronger and firmer. This altered cell structure is called reaction wood, or sometimes stress wood. Trees that exposed to strong winds early in life become trees that can withstand even stronger winds when full grown. Conversely, trees that are raised in a protected greenhouse sometimes fall over from their own weight before they reach maturity. Stress wood is a perfect metaphor for children, who also need to experience frequent stressors in order to become strong adults.” – Jonathan Haidt