Making a woods themed base is much easier than I thought it was going to be. There are some things to consider when going with this theme, but I was surprised at just how quick it all came together. I'm going to show you how I made the one you see above.
What I used to create this base
GW Static grass (the bright green stuff)
Secret Weapon Minis Blasted Wetlands base
Material to represent the fallen, dead leaves
Material to represent moss and mold
Material for some taller bits of grass and such
White (PVA glue)
Material for tree stumps
I have a good bit of basing material from Secret Weapon Minis. I used a number of their products to build this base. While using their stuff makes it super easy (and I mean super easy) to do this, it would be wrong to list just them when you could do this with other materials as well... it may not be as easy, but there are options out there.
This post here talks extensively about using materials you find around your home.
Alternatives to buying the materials
The fallen, dead leaves: Secret Weapon Minis Fallen Leaves - Brown
Alternative: You can use brown construction paper and give it a variety of washes using browns and blacks to create a varied colored material. You'll want to do it on both sides of the paper though. From there, you can use your X-Acto knife to cut out a handful of leaves you can use.
I did this very thing for my first attempt at leaves on this base here.
The turf and taller grasses: Secret Weapon Minis Instant Scenery Kit Grasses
Alternative: These might be tough to replicate. You can shop around as there are a few companies out there making grasses and such. The trick is to get the color you like.
Dead tree stumps: Secret Weapon Minis Tree Stumps
Alternative: You can use small bits of shredded bark if you can get your hands on some. Take your X-Acto knife and cut one end flat for vertical stumps and break apart pieces until you get suitable sized ones for horizontal stumps.
Bases: Secret Weapon Minis Blasted Wetlands
Alternative: I will say that it's worth using the Secret Weapon Blasted Wetland bases for this though. They have the stumps already on them and it saves you a good bit of time. But... you only have tree stumps on there. Making your own might allow you to incorporate other elements like rock outcroppings and such.
You could do this with just about any base line really when I think about it. I went with the Blasted Wetlands for the "woods" look as opposed to the rock or overgrown ruins appearance.
Why woods bases can be hard to replicate
Woods can be tough to replicate because there is so much to woods that is not on the ground. Lots of times, our basing theme comes from what is on the ground. We don't show many elements that extend much higher than a foot or so in the model world. This is why woods and jungle can be harder to pull off than other basing themes like snow covered rocks. So much of what makes up "woods" is off the ground.
So we have to be spot on with the ground elements when we can't use what's around the model to help convey the atmosphere.
After looking at a few reference pics. I decided I would use a few key elements in my "woods" to create the feeling. I knew the tree stumps and fallen logs would play a big part in it. I wanted lots of dead leaves on the ground with patches of grass here and there. The last bit was some mold/fungus type growing on the dead trees.
Once I had my base primed black, I gave the stumps a heavy drybrush of GW Stormvermin Fur and the ground a pass with Rhinox Hide. You could use any grey and dark brown really. Once those were dry, I started adding my vegetation.
The first thing to go down were the leaves. I covered most of the base with these as the ground in most forests is covered with them as well. On top of that in some places, I added the GW Static grass. I only added it to places I thought it would be damp enough for grass to start sprouting up and what looked good from a visual aspect (even if it was "wrong"). Places like right next to the log. That led me to the taller grass. It went in the low traffic areas and tucked into corners if you will.
When adding the material, I took my white glue(PVA) and mixed a little bit of Rhinox Hide paint directly into it so it matched the ground color and spread it around where I wanted the material to go. I went kinda heavy on the glue so I'd have enough to actually hold onto the larger material pieces. Sprinkle the material on top of the glue, shake loose the excess and move on to the next step.
With all of those pieces in place, I wanted to add some moss to the tree stumps to tie them to the ground. I also added this for a variety of textures. I thought if I could get a few in there, it might appear a bit more realistic.
I did go back and add a few more leaves in the end to get some more brown in there. You can see that not much of the original base is showing in the end.
What you need to know
This process goes quick. The base took me about 10 minutes to do (not including drying time). A whole squad could be done very quickly.
The biggest thing is doing this without your model in place. You need to do these separate from your models. Since you end up with so much material glued to the top of the base, it's important that you pin your model to the base as well for a solid connection. Simply gluing your model onto the leaves will not provide you with the support you need for gaming.
As far as varnish, I suspect you could get away with varnishing your models after you have attached them to your completed woods base. I'd be more inclined to varnish them before attaching them though just to be safe.
Make sure to check out these posts as they might help:
Basing your models with free stuff from around your home
How to make static grass stand upright