Today, April 28, is Arbor Day in the United States, where I live. Many other countries and cultures have an annual day to celebrate and plant trees, the exact day depending on their climate and culture.
Trees lead active, informed lives, paying acute attention to the world around them. They can’t get up and move, so they have to cope with whatever comes their way. Here’s some of what your tree knows:
A tree knows where it is. It knows up from down, and its sense of gravity allows it to grow up without mistakes. (Plants grown in weightlessness in space sometimes get confused.) A tree’s roots tell it all about the soil and its composition, and the tree will sense the roots of its neighbors and know what they are. It knows which direction the sunshine comes from and can arrange its leaves to capture the maximum light.
A tree knows the seasons. The angle of the sun and the length of the days let it match its growth with the seasons. Dandelions illustrate this well. They get ready to bloom in the spring and fall when the days are between 12 and 13 hours long. This sense also helps seeds germinate at the right time of the year.
A tree knows the neighborhood. Plants nearby may emit chemicals into the air to warn of attacks by insects or other trouble. The tree will know if other trees of its own kind are nearby, too. Trees usually prefer to grow in communities that can share food, information, and protect each other from violent weather by acting as mutual windbreaks.
A tree knows when you touch it. It can also feel hot and cold, and tell when its limbs are swaying in the wind. Plants prefer not to be touched, by the way.
A tree knows a lot about the weather. Heat, humidity, sunshine, storms — it has to cope with whatever happens and can adjust itself in many ways. Leaves may get tougher to cope with hot, dry days. The tree can have a growth spurt when the weather is favorable, or go dormant in especially hard times, waiting for the weather to return to normal, and it remembers what normal was like.
A tree knows when it’s had enough. You may notice that in a climate where trees drop their leaves in fall, some trees start to drop their leaves earlier than others. Trees spend the summer storing food to get through the winter and resume growth in spring. It can only store so much. Trees lose leaves for winter because the weight of snow and ice on leaves in high winds might pull down a branch, which can be a fatal injury. When a tree’s storage is full, it makes sense to drop the leaves, start to doze, and stay out of trouble in case of early storms.
(Photo by Sue Burke)
Semiosis 
Arbor Day celebrates tree planting across cultures, highlighting their amazing abilities. Trees have a strong sense of location, knowing up from down and adjusting to their surroundings. They can detect the seasons, nearby plants, and even when touched. Trees are sensitive to weather changes, adapting accordingly and knowing when to shed leaves based on their internal storage capacity. #ArborDay #TreeIntelligence
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