Trees provide a buffer against winter winds, and moisture transpiration in the summer acts as natural air conditioning. One study by the Federal Energy Administration found that a large, vigorous, well-watered hardwood tree has a cooling capacity of 800,000 BTU's per day. Place a thermometer in the lower branches of a large, leafy tree and one in an exposed area. Compare the temperatures shown at both sites on a hot afternoon. That's enough elephants to reach from Columbia to London and back again.
Trees also help manage the amount of particulate matter picked up and carried by the wind.
Vegetative windbreaks, consisting of several rows of trees, are utilized by farmers on the great plains to slow the force of the wind and prevent topsoil from being blown away. Aesthetic appeal is very subjective, but it can translate into things more quantitative. Parks, camping areas, and tourist towns depend heavily on their appearance to attract tourists, and much of this appeal is based on trees and landscaping. Noise reduction is a specific area where trees can improve people's attitudes and enjoyment of where they live or work. Sounds in the 120-140 decibel range can actually be painful.