Also, to vin, about finding trees like this; this tree was collected from the approximate middle of a large field (about 220 acres). Here (Central Texas) these tree are treated like an epidemic. They grow quickly, spreading out and covering usually arable land where they're not wanted. This tree, along with almost all the others I've collected, have come from large empty lots frequented by large amounts of cattle. They stomp the younger seedlings to the ground, breaking them off and forcing them into thickening to raise their head, or otherwise them into interesting, tortured shapes.
So far these sorts of open meadows, surrounded by thickets of live oak, scrub brush and Ashe juniper, frequented often by cattle or occasionally by tractor and plow, have been my best harvesting ground. The local ranchers have been known to attach heavy gauge wire to logs and metal bars and pipe, making a long row with a pair of tractors, one at each end. They'll drive slowly back and forth across these meadows dragging the line, breaking off all small vegetation off close to the ground. If they don't use this method, either controlled burns or just plain old plowing with disc or blade plow are used to keep the areas these trees are collected from free from large brush growth.
Between the efforts of man and the clumsiness of cows, any trees more than 5-8 years old are sufficiently interesting (usually) to warrant their collection in my eyes. After finding such a place, the only work is the digging, and the finding of the best trees out of the whole pasture to collect.