Concerning the modeling of trees: It appears that this process is a somewhat complex one requiring several steps and operations. It also appears that the realism is dependent upon how many leaf textures can be used in the process.

Now before I make the suggestions I have in mind, I need everyone to understand that I have no experience with this at all. These are things that I thought of as I read the last few posts in this thread, so my ideas may not have any merit. Anyway the following are a few suggestions I came up with.

Suggestion 1. Create a simple tree model with few branches. Duplicate this tree several times. Change the branch positions on many of the duplicates. Give one tree a small amount of leaves distributed sparsely among the branches with one leaf texture assigned. Do the same for the duplicates but change the leaf positions and assign a different leaf texture for each one. Bring all of the different trees together in the center of the modeling grid in the 3D view window. Join them to make a single group. I don't know if this would work, but it seems like a logical approach to reach the goal of realism. Of course there would most likely be the need to ensure that certain parts of each tree do not overlap, (you wouldn't want the final result to have oversized or weirdly shaped branches, etc.).

Suggestion 2. Once you have created your tree but before doing the leaves, divide the branches up by means of selecting series of verts, hitting [P], then choosing selected in the dropdown menu. (This will effectively make separate objects each time you do this.) You only want to do this where you plan to "grow leaves", and each branch should be divided into several sections. You can make individual sections of every branch together into one separated object, (a process I call "Mat Zone Creation"). Now go to Object mode [Tab] and select one of the new separated objects. Return to Edit mode [Tab]. You should now have a series of branch sections from all branches of the tree in vertex mode. Assuming you have already modeled your leaves with separate leaf textures, use the method that grows a leaf for each vertex of the currently selected object. Now go to Object mode again and select another of the separated objects. Return to Edit mode, and repeat the leaf growing process, but assigning a leaf with a different texture from the first. Repeat this process for each of the remaining separated objects, making sure you are using a different leaf texture for each one until you have done all of the ones you want. Finally, return to Object mode, select all objects (excluding the camera and the lamp), and then Join them together into one group. You should now have a tree that has leaves with several different textures. I don't know if this will work, but if my way of "Mat Zone Creation" works for the models I create (in which I create paint schemes for my models), I don't see why it wouldn't work for this purpose as well.

As I say, I have virtually no experience with creating trees in Blender. The above are just some suggestions that I thought of that may or may not work. If anybody tries them, let us know the results here in this thread. It would also be nice to see a render if one of my suggestions works. I am not as advanced in my skills as others in the use of Blender, so it will be some time before I can do certain operations that would be required for success in creating a fair looking tree. I am still studying the process that converts verts into objects such as leaves.

Stay awesome!

Agent 0013.