When you see a Tree; what do you see? Do you see shade, beauty, wildlife habitat, house, cabinets, fire wood or special projects. I have spent over 45 years managing, harvesting and reforesting large tracts of forest land and I see all the above. Retirement has brought me to a specialized hobby, turning bowls with a wood lathe. So I am always looking for wood with a unique natural wood grain pattern, color, shape and size. I generally work with wood native to the area where I live; but with the internet you can get wood from any where in the world. I am always looking for wood to turn a unique bowl.
I am not advocating grabbing your neighbors chain saw and running out into the Forest and cutting a tree down, that will most likely get you a hefty fine or jail. Watch for storm damaged trees and construction sites where trees have to be removed. Logging sites always have material left over that will have to be disposed. Hazard trees that have to be removed from over highways or power lines are a good choice. Usually qualified professional people will remove the hazard tree and place it in a safe place. ASK PERMISSION first that will make friends rather than enemies.
Most of the time I am looking for small pieces that are about 2 foot square and 6 to 8 inches thick, your project will dictate the size. I always get pieces several inches larger than I need, then trim the wood to size at my shop; this gives me the ability to work around some of the defects I didn't see in the field. Storage is always a problem, you can only store and dry so much wood, so I am cautious about how much wood I drag home.
I recently picked up a Maple log that was hanging over a power line. When the tree was on the ground it involved 3 large pieces from 2 to 3 feet in diameter and 10 to 20 feet long, that is a lot of wood. I contacted two other fellow wood turners and between the three of us we removed the tree and milled the wood. The Big Leaf Maple (Acre macrophyllum) had some very nice fiddle back and quilt grain and some fire wood for winter. I now have several nice bowls in the kiln and more to be turned.