Wind is caused by trees moving around, in a similar way a fan moves air (have you ever noticed that when the trees are still, there's no wind?)
Some species of tree are more active than others, which accounts for the gusts you ask of. Palm trees go through cycles of inactivity for months at a time (almost dormancy), followed by the rapid waving of their fronds. Palm fronds are particularly good at moving air, and when enough palm trees move at once, they can produce what we call a tropical depression (or Cyclone/Hurricane).
I live in a tropical region, and keep all my palm trees neatly trimmed, thus I have not had a single Hurricane since I've been here. I wish more people would be as vigliant.
I hope I haven't been to scientific.