I have Vue4, Vue 5, Vue5I.  I have Bryce 5, and now 5.5.  I own Shade 7 Standard.  I own Lightwave 7.5, 8, and now 9.  I own Carrara 3 and Carrara 5.  Own Poser 4, Poser 4 ProPack, Poser 5, and Poser 6.

Seems like a lot huh? Well there is no one application for the job.

If you mostly concerned with trees, terrains, and poser stuff then I would sugjest Bryce or Vue.  Bryce has a slow renderer but it works.  Vue is amazing when it doesn't crash or bug glitches.

You can grab Bryce 5 free and then upgrade at Daz for $19.00 until this week.  Vue is haveing a sale where you buy any version of Vue 5 and get the corosponding upgrade to vue 6 free.

There is not a simple way to get Poser content, Bryce, or Vue stuff Into Lightwave.  Vue to lightwave is a bit better now, I've only read about the xtream lightwave vue5i to lightwave plugin and what I've read hasn't been that impressive.  Plus the plugin is expensive.

Carrara 5 has been the easiest for me to get poser content into and render. simple fast and efficient.  Carrara also has a terrain editor that is very similar to Bryce as well as trees.  not as good looking as Vue, but very capable.

I'd recommend Carrara 5 pro, Bryce 5 free then upgrade to Bryce 5.5 (Bryce 6 upgrade only for 5 and 5.5 owners).  Maybe Vue ontop.

There are pleanty of free to cheap modeling applications.  Wing3d, Silo, Blender, Hexagon.

Save your money and don't go Lightwave.  If you do poser stuff lightwave will be a bit overkill for your needs.  I really recommend Carrara 5.

My buck and a quarter.