Thanks Shawn, I am very glad you like my work, as for my part I just love to make the plants and landscapes for dioramas as much as the animals themselves.
To answer some of your questions, I have done several step by step diorama builds, the most recent being here:[You must be registered and logged in to see this link.]
I plan to do a step-by-step tree tutorial as well.
My dios are done from scratch, first I pick a habitat or scene I want to recreate, than I cut the base out of wood in the size I want. Like Shawn I use foam to build up the topography, you could easily use other materials but try to keep it light, things like clay, wood, or real rocks work but the cost of purchased materials and the added weight make it impractical to use.
Once this is done I cover the landscape with some sort of material that will be the "dirt", I use paper mâché ow plaster cloth, both are very inexpensive, easily shapable and dries hard but very lightweight. At this point I paint the whole thing a earth tone to give it an even base to build on.
I won't go into each of the landscaping details here, look at several of my dio posts or PM me if interested but at this point I start to sculpt the rock work, trees and bushes, any grass or dirt areas as well as stream banks. I use many different types of materials, I have posted lists of what I find works for me in other posts but let me just say there are no right or wrong materials, use what you like and are comfortable working with.
Here is a partial list of materials and how I use them
Durham's wood putty-tree trunks and rock work
Paper-palm fronds, smaller plants and flowers
Sculpy polymer clay-figures, smaller trunks and branches, rock work, larger leaves and flowers. Clay could be used to sculpt just about any part of a diorama.
MagicWater-water features, streams and ponds
Bleached horse hair and nylon yarn-grasses and fine details
This is far from a complete list but it should give you a good start on ideas for which materials you can consider working with.
I will end here so everyone isn't overloaded with info but in the next days I'll respond with other procedures and materials I have found to be best for me.