It's a good thing if you can't move the trunk; that means a dense, fibrous root pad has the tree strongly adhered to the rock substrate. One very important thing you must not do and that is use the trunk for leverage to get the tree out of the rock!! As I mentioned above, start from the edge of the hole and gently work down to the bottom of the pocket and do this all the way around. Take your time and do it right, after all it took hundreds of years for that tree to attach itself to the rock. It's only fair to take the time to do the job right. I carry a spray bottle to keep the rootpad moist while I pry the tree out and lessen the shock. If it looks like you're going to damage the tree trying to get it out, it's best to leave it until you get more experience. Those are some nice old trees and not worth killing due to lack of experience.
People think that collecting is slam/dunk easy to do. They are wrong! There is an art to it--one first has to develop an eye for what is good material and then the judgement/ability to see it through to the tree in the pot that we all desire. This can only be achieved through years of practice, trial and error and yes, killing a few trees
May I ask what tools are in your backpack for collecting such trees
