In digging material up from the wild, you're after stuff that has character and some size.
The tendency for those just starting out is to think really small in terms of material. That can be difficult, since the smaller the tree, the more skill needed to make it into bonsai--less of everything to work with--smaller trunk, less roots, less leaves, etc. Care is also more difficult for smaller trees, as since they have smaller pots and less soil, they are more demanding when it comes to watering. They're also more quickly affected by disease--less plant, less time a bug or fungus needs to affect it.
Think BIGGER by at least five or six times (or even bigger) the size of this tree when collecting stuff. Don't be concerned with a possible candidate plant's initial height. It will be reduced substantially. FWIW, I've dug 30' tall bald cypress and cut them back to 36" in preparation for making them into bonsai. You're after TRUNKS when collecting trees.
In collecting from the wild, you're after only the bottom third of a tree's trunk (pines excepted). If the first 12-24 inches of a tree's trunk has interesting qualities like good "movement" or fine bark and/or nice root spread, the rest can be worked out. New branches and canopies, for the most part, are completely regrown on trees that have been cut back severely at collection.
For the most part, ignore seedlings. They're not really suitable for bonsai work. They're nice to collect and grow out, but for the most part, you won't be "bonsai" them for a decade or more.
Below is an example of what to look for when searching in the woods. It is a bittersweet vine that was 50' up an oak tree. In early April, I cut its roots and chopped the top off and put it in a container. The species is a strong grower and it is currently pushing new buds. I plan to allow it to grow without any work this year and probably the next to gain strength. The new buds will develop into the bases for a new set of branches in the coming years.
This is an easy species to dig, as are wild wisteria, any elm species, Carolina hornbeam, and a few others that live in your area. If you're interested in collecting, get a species guide for your region, learn what your local species look like and where they grow. The best time to find potential candidates is in late winter, when there are no leaves and the insect and reptile population is asleep.
Lastly, get a copy of Nick Lenz' "Bonsai From the Wild." Although he focuses on Northeastern and Western U.S. species, his advice on how to dig trees is about the most accurate out there. Collection advise in most bonsai books is crap, written by people who don't really have experience digging wild trees. What you read in most bonsai books completely breaks down when you actually dig a tree.
