I'm not going to lie, when i saw Eloth mention trees and flora as something that needs to be done I took a big sigh. However, after a few weeks of practice I thing I've got a good technique down, although there are still a lot of kinks to work out. I never beleive in exporting anything to my precious Skyrim installation unless it's finished and clean. So getting straight to the point, I would like to show some screenshots of what I've been working on.
First Attempt:

Pretty bad huh? Well it get's a bit better thankfully.

Still kind of bad but after some sculpting it comes together.

Hopefully I'll be able to export these(after some poly reduction) into the game. But I posted this as a way to get some kind of feedback on what I'm doing, maybe I should just edit the existing trees instead making new ones. I feel as though adding new trees will make that Morrowind forest environment seem more diverse and organic. Let me know your thoughts.

Doing it by yourself might be daunting, why not make more specialized trees like you have now. and for the rest use existing modders resources on skyrim nexus then modify/retexture those. One of the tree authors has already authorized usage of his mod in skyblivion. this would allow you to keep on adding unique and morrowind esque trees. and also modify existing new resources to save yourself some time.
Personally I like the work you have posted. :)
Thanks for your feedback! I agree that at first, it was a daunting task but I think I have a good technique down for this tree-making bussiness. I've never been more interested in trees :D
Are you willing to use Speedtree in order to reproduce the defauld Morrowind trees into the Skywind tree standard?
There were no speedtree in morrowind (the default trees were converted but they are really outdated now : / )
For the ashland trees I think the vurt trees are really the best we can have
vurts trees is just too much, would be better to improve the morrowind ash trees, and add animation to them
I know there where no Speedtrees in the Morrowind files, but I got the programs up and running, if someone wants to have fun with it just ask.
Those might be a tiny bit over the top, but Vurt really does some great work. I've never played Morrowind with his tree mod, but I bet there are some models we should use.
I don't use them as replacers, but a few of them really add a dark atmosphere in the ashlands...
maybe you prefer this ; ) (also from vurt)