They look fine to me, but put a bit more grass to make it seem like they are connected and the on e at the back should be smaller than the one at the front.
First off, I wouldn't recommend texturing the bark like that if the leaves are going to be left blank. Right now the leaves are way to smooth, the should be more defined so you can tell that they're leaves. Having empty spots in the tree where you can see through doesn't look very good, mainly because the head of leaves is untextured and undefined so it makes it look flat. If you erased the bark texture and the empty spaces, and then gave the leaves some cutting edges it would look pretty decent. This is what I mean by defining the leaves.
Not texturing can look better than texturing. Although if you redo your bark definitely ditch those short lines, Make the lines longer and keep in mind where the light is coming from when your doing it.
I agree for when the tree is in the background, but mine is in the foreground and needs texturing. ps. i was looking to do something like this: http://www.how-to-draw-and-paint.com/how-to-draw-trees.html
Here's some quick texturing I did, I think it's similar to what you want. I wouldn't recommend detailing as heavily as this but I hope it helps.
I pretty much agree with everyone else. Looking at the guide you were following I say forget that. Maybe you should try a different approach to doing leaves/tree. That might help you out. Firstly do the tree itself with all its branches. When you have that done add mass of leaves to the end of each branch. Doing it like this will probably give you a better idea of what to do by yourself and it will set you up in making a more realistic looking tree.
For your particular look that I think you are trying to achieve I would say small lines varying scenery and physics lines. Looks great!