When would be the best time to transplant small trees?

in South Texas (just NE of Houston)

and what's the best size to insure the best success?

We're talking mostly oaks, pines, maples

Are the trees in the ground? Are they in the wild, or in your garden? or are they potted?
The best time to transplant trees in Texas is in the fall when they are dormant, but if they are potted it still can be done before it gets hot.
Small trees 2 or three feet and smaller transplant better than larger trees, but a lot depends on many factors.
Josephine.

Sorry, Josephine. I should have given more details.
We live on 5-1/2 acres, and have cleared about 2 acres now.
My husband does not do any sort of 'preselection' before he runs the bush hog *hrmph* so we've lost way too much shade now as a result.
I'd like to transplant some that are growing in the wild, in areas he's not yet touched, to areas where he's destroyed, er 'cleared' other good trees.

I'll mark them this spring/summer for transplant in the fall.

thanks so much for your help!!