Remy is right. That's a good first map.

Looking forward to seeing more from you :)

I think I may have a scale issue here. Because I've never seen any of these trees for real I can only go on what Google says is the height range for each one, which is altogether rather vague. So here are a few I'm not sure about next to each other. Please feel free to comment.

Are the Joshua trees too big? Are the gum trees too small? Are the saguaro too big or small?

Not sure if they would double for birch because the leaves are quite dark, but you could scale them differentially to make them slimmer.

Been working on everything I've done so far together today - to get things like relative contrast and shadows right. The Joshua trees are in the pipeline, but not yet finished.

I think I'm finally happy with the palm trees.

(work continues on all fronts, so don't think I've forgotten other types of tree)

Ok. How about this one? I managed to get it to look a bit taller by shortening the lateral branches a bit. It's all relative. I also managed to get the fronds to clump a bit more and show more of the branches, like the real one, by removing a lot of the distortion on all the stems. This might seem to make them a bit too straight, but at the size they will be in an overland map I think it will be ok.

Now back to the palms for one last try at making them look like something decent, and then the swamp trees and general jungle trees.