The author tree is not exactly a distinct botanic species. Author trees can be Elm, Maple, Oak, or any large deciduous variety. In tropic and hot climates Palms and Baobab trees have been very successful author trees. Pine and Fir are less common, though the Giant Redwood of California would be very suitable, if a little deadly.
You see an author tree is a tree which the author of a book that is not selling well will use as a marketing tool. He packs a bag with copies of his book, climbs up the tree, and shinnies out on a limb that hangs over the sidewalk.
When a suitable victim walks under the tree the author drops the book on their head and then pops back into the foliage. The person below suffers a surprising blow on the head and then looks around to see who threw a book at them. Very few ever look up. Then they pick it up and see what it is. In most cases they will start to read it…and if the author has been careful the start it put with a zinger like a murder or a girl taking her clothes off, chances are the sore head will wander off reading the book.
It was not a marketing strategy without risk. Pamphleteers and writers of short stories bombarded the populace with no qualms; their writings were lightweight and safe to drop. Others, like Tolstoy or Zola, caused fractured necks and worse. This explains many of the periods in their lives when they took rapid vacations into the provinces.
Of course you have to make some sacrifices for your art, but these days sacrificing strangers is not viewed well by the authorities. Philistines to a man.