I'm trying to get as realistic an environment as I can acheive with Bryce with Landscape. does anyone have any tips of how I can improve?
Here is my latest scene....
http://www.renderosity.com/mod/gallery/index.php?image_id=1637449

I've experimented with hdr lighting, depth of field and now movement.

Lots to consider.

Light, shadow, dof, textures, content.

This image looks pretty convincing, what hinders the "real-real" factor, Over blur on the bottle and the grass is not bending in the wind. The windy feel to this is fantastic.

Landscape realism is tough, I'm not patient enough to tweak for along time to get these results.

Might also try a GI dome, or Zenith light along with HDRI/IBLs. When you use IBLs, match the IBL colorscheme with the enviroment you're working with.

I've tried a few, but few really successful end products.

Lookin good.

Keep'm comin.

The first one has the lighting turned up pretty high.(as high as I could get it without washing the mats out completely)

Second one is the same render, I used it as an overlay layer in PS with 75% Multiply effect.

Was trying for Stark sunlight with a mix of soft & deep shadow.

the small black artifacts are the plant. It's not fully above-ground.(these could be fixed with post)

Only an experiment, no skulls or plants were injured in the making of this scene.

I already gave up on giving a lot of realism in landscapes with Bryce. 
The great secret is still the work with textures, illumination, shades and a lot of patience. 
 
If you approximate a tree a lot for instance the texture it distorts, it stains, it is horrible. 
The distãncia of trees, grams, and other objects can disguise certain imperfections. 
 
The realism will depend the landscape it was made simulating day or night or even a certain schedule, that because the natural illumination of the atmosphere will influence in the final result. 
 
I considered a high degree of realism in the mentioned image, but still the objects in first plan, as the bottle and parts of the tree leave to want, they are stained, but that can be an interesting effect. 
 
I eat the textures naturally they can inherit the composition of the atmosphere (color, brightness, refraction and reflection) I would be devoted to a study on textures, illumination, shades. 
Also consider a lot of creativity and hours testing to same textures with different configurations in your properties. 
 
Hugs

The first image looks more like a spontaneous photo of what looks like a crime scene....  

nicely done

Good points ICM and Thandaluz. What exactly is GI dome?

Global Illumination.

A dome of radial lights. I think there is a set up in freestuff.

Oh thanks mate, i'll take a look.

Ok, downloaded it, placed it in the preset folder, how do I use it?

Oh.. I see... LOL! Got it. Thanks. Wow! this looks interesting.

When I have toyed with realism in landscapes.  I have found two things that help tremendously: hi-res terrains/material and low angle lighting with soft shadows.  Both are resource and render time hungry.  There are not many times in nature that shadows are as sharp as a default Bryce render.   I have had mixed results with outside HDRI lighting.  I can't predict what the resulting render may look like.  That is probably my failing and not enough practice.

@ dhama

I would agree with ICM that grass doesn't jive with the MOST EXCELLENT motion blurred leaves.  Another pitfall of Bryce trees in shown in your image.  They can't be bent in the wind.  The background tree line is too uniform for my liking. 

Quote - Another pitfall of Bryce trees in shown in your image.  They can't be bent in the wind.  The background tree line is too uniform for my liking. 

Indeed they can't.... i'm still waiting to see if my tree maker DesignFera can come up with a wind swept tree. Anyway, it's just another Bryce limitation that i'll have fun finding a workaround for.

It would be so much interesting as challenger sees those difficulties committees in a challenge. 
A challenge on wind, to bend trees, grams...

The only thing I can even think of suggesting is that your specularity may be off on the ground textures.  I would guess you used "mossy rock" or some variant like that.  But the sides look glossy to me.  Maybe something with a little noise in the dirt would help too.

I dunno if that would help or not.