For some ferns there are vanilla models, but not all. I would love to have Bracken (Pteridium aquilinum), but then a new model is needed, probably not a very complex one compared to your trees

There is one vanilla grass model that is used for undergrowth, but it is a bit weird and hard to make work. http://1.bp.blogspot.com/-hfl4pbeNCy8/T3a_ASnNGjI/AAAAAAAAAhg/afrcpiLjuBY/s1600/forestgrass01-2.jpg
Most of the ground covering plants have up turned leaves, with leaves at similar height, and there is no need to see the leaf stem. http://imageshack.us/photo/my-images/560/undergrowth.jpg/
I'm thinking that a simple model could work, perhaps a slightly bent vertical sheet would work. At least for the plants that are not higher than 10cm.

I have almost all images needed to do textures of undergrowth plants, or I can take trip out into the forest now that spring is here. But I have no idea how to do new models for them.

Sounds great!
If you want you can post the pictures here, and I could try to make the models with them. I would post wip pics of the models and we can discuss what needs improvement or change.

That sounds like a great idea
Anything specific that we should start with? If not, I'll get to work on some leafy ground covering plants if you don't have any other favorite forest plant you want to start with. I will bring the camera to work tomorrow, I have already noted some good places on the way there today.

Ground covering plants sounds like a good start to me.

I have some suggestions on low and medium height ground cover plants, that is 1-10cm.
http://s1164.photobucket.com/albums/q568/elinen/Forest%20plants/

Ok, here′s a first ground covering model from your pics (it uses one mesh as seen in the second screen, but can be arranged like in the first or third screen): http://www.imagebanana.com/view/4ghrbt6z/2.jpg --- http://www.imagebanana.com/view/hzgteaid/3.jpg --- http://www.imagebanana.com/view/hv0l2edd/4.jpg
If that′s what you had in mind, I can make the other ground plants from the pics too.

Btw, you probably know about Vurt′s textured trees? Well, I have his mod (it′s awesome) and tried a retexture of his aspen trees. Could be useful for forests (but he has to give permissions first, of course):
http://www.imagebanana.com/view/yop8xu3e/1.jpg

That's what I had in mind, it looks nice
I like the re-textured Aspen too.

I can fix the pictures, I have higher resolution pictures that the ones I uploaded, I'm thinking that having them in 512, 1024 and 2048 would be good.
I have uploaded some pictures of higher plants, some different ferns and a bamboo like plant I found in a forest in Ireland.
http://s1164.photobucket.com/albums/q568/elinen/Forest%20plants/?action=view¤t=high-WoodHorsetail.jpg#!oZZ2QQcurrentZZhttp%3A%2F%2Fs1164.photobucket.com%2Falbums%2Fq568%2Felinen%2FForest%2520plants%2F%3Faction%3Dview%26current%3Dmedium-fern1.jpg, http://s1164.photobucket.com/albums/q568/elinen/Forest%20plants/?action=view¤t=high-WoodHorsetail.jpg, http://s1164.photobucket.com/albums/q568/elinen/Forest%20plants/?action=view¤t=high-fern2.jpg, http://s1164.photobucket.com/albums/q568/elinen/Forest%20plants/?action=view¤t=high-Braken.jpg, and http://s1164.photobucket.com/albums/q568/elinen/Forest%20plants/?action=view¤t=high-bambu.jpg like plant.
Do you think these will be good as larger undergrowth?

What do you think about adding to the simple model you made to have flowers on wood anemones?
http://s1164.photobucket.com/albums/q568/elinen/Forest%20plants/?action=view¤t=medium-Woodanemone.jpg

That looks really nice!

Ok, added thin stems so it gets a more 3d feel (I am not sure if the size is correct, might be a bit too big) and did some more variations (fern, woodanemone etc..): http://www.imagebanana.com/view/rsiy1hfp/1.jpg --- http://www.imagebanana.com/view/pciufqze/2.jpg --- http://www.imagebanana.com/view/n9ocwjpv/3.jpg --- http://www.imagebanana.com/view/kkz2d7li/4.jpg --- http://www.imagebanana.com/view/98zvtw2i/5.jpg

impressions welcome.

That looks really good! The stems seem to add a nice thick ground layer for forest. I'm especially a fan of the ferns.

The wood anemones looks really nice, and I really like the fern!

I worked on a texture for woodland Crane's-bil. I'm thinking there could be a variants with and without flowers. There are lots of different crane's bil so I included some different colored flowers.
The file is a Photoshop file, in layers for different leaves and flowers (didn't know how you want the layout for the texture).
http://www.mediafire.com/?7es8xmm2u6gmov7

Worked with the woodland crane texture and made some variations. Also made a stinging nettle and 2 more ferns.
http://www.imagebanana.com/view/tx0lzli3/1.jpg --- http://www.imagebanana.com/view/7mge1krs/2a.jpg --- http://www.imagebanana.com/view/bjvm7n3f/2b.jpg --- http://www.imagebanana.com/view/z9a9143m/2c.jpg --- http://www.imagebanana.com/view/b1wnn1bw/3.jpg --- http://www.imagebanana.com/view/0mqnd1wq/4.jpg

These and the other groundplants are basically done, because they don′t need animations like the trees and don′t need collision neither. So here′s the download link if you want to test them out: http://dc609.4shared.com/download/UlrZ_nGk/ztrees_groundplants1.rar

I hope everything works as intended, but if any texture is not showing correctly or something just post here and I will try to fix it. I hope I can release my trees soon as well, but you know I don′t want to just give them out without any collision or anim...Want them to be fully finished, before I toss them out there.

Trees use primitive shapes as collisions mostly and it's possible to create and export such shapes in latest MAX plugin (3.7.3). As for anims, I suppose you mean creating the rig (bones) and skinning the tree to it, because it is exactly how the animations influence the trees. Though here the point is that they use nodes with unrecognizable names, and with some additional data not yet supported by import/export plugins. In short, it means that making trees with collision is possible right now, but for proper handling (import/export) of those new node structures we may wait even for couple of months for the right tools to be released. So it's your choice after all :] either to release now some trees with collisions only, or wait, no one knows how long, for implementation of proper import/export of that new content.
In theory, such skinned tree could be made right now I suppose, by creating a new rig, then skinning the shape of the tree to it, then exporting the content, and "painfully" copying/pasting/fixing certain data between exported and original nif.

Yup, I want to try to get some sort of primitive collision working on the trees. Have to look around for tuts. You are right, for the first release I don′t really need anims yet.

The woodland cranes turned out really nice
I'll keep working on and cleaning up more textures. I have lupines, common Dog-violet, bitter-vetch, columbine, meadowsweet and some I don't know the name of.

I did a new leaf texture for the wood anemone, and I also did some more color variants.
http://s1164.photobucket.com/albums/q568/elinen/?action=view¤t=woodanemones.jpg

Looks wonderful! But perhaps too strong green saturation? (I'm not sure, but I imagine it being too strong for Skyrim's kind of dull colors, but then again this resource could also be used in other landscapes!)

I hope someone will place all these too. It would make walking in forests much more enjoyable

I can make a less saturated version too. You are probably right that it's too much color for vanilla Skyrim. I think I will keep this greener version also for more lush and green forests in other worlds

cool, nice work there

Noob question: the animation of tree branches are affected by heavy climate like wind/rain ? ( "shaking" effect like in Oblivion)
If yes: what are the settings to obtain "shaking" effect with custom tree models ?

That sadly doesn't appear to be the case, as far as I've seen they always move in the same manner.

I'm not 100% sure, but I think it will be possible for us to eventually create Behaviour graphs for our custom trees and then implement different animations depending on weather. It might be quite heavy on performance though.

I wonder if you could ask a dev kindly and send all the trees you want animated to him/her to make them animate...
Or maybe not even have to send them, but just ask how so maybe you can do it yourself.

Devs have been much more helpful with Skyrim than with any other Bethesda game before. They've even made some really good mods!

So far most of the plants I have textures for are ankle high, with the exception of the ferns ztree made. It would be nice with something knee and hip high as well.
One idea is http://i1164.photobucket.com/albums/q568/elinen/Forest%20plants/Meadwosweet-Filipendula-ulmaria.jpg, anyone has any other ideas?
(Meadowsweet can even be head high when it grows under good conditions)
Ztree, if you think this will be a good addition, I have made that textures already
http://www.mediafire.com/?y2a3g7cofor5a4b

I think meadowsweet would be a nice addition ^^

Another possible tree (if it haven't been made already) is a different kind of pine tree. I don't know the English word, but in Swedish it is called "tall".
It looks like this: https://encrypted-tbn1.google.com/images?q=tbn:ANd9GcS6PeztimZ7WR1f4vyk_2do1b2OsjjyCJYUs8P8eJJsD-j_Felo, http://www.cartinafinland.fi/sv/imagebank/large-image/91/91004/tall+91004.jpg
Common in sandy and rocky areas. It would fit the Reach and the volcanic tundra very nicely I think.