Thanks 
The trees are from mahonia plants..they grow like weeds and if you pull the roots out, knock any earth off and then put in the sun or on a radiator they dry very well. mahonia is also a very hard wood so it doesn´t shrink or splitt.
The Rocks (left and right ) are from Pine tree bark, painted black, then dry brushed in grey.
The wall in the middle is made from insulating foam, the pattern drawn on and some bits cut with a scalpel.
The snow..plaster of paris. I put a bit of watered down woodglue on the areas I wanted , then with some plaster on a small spoon, I pushed it off onto the glue with an old paintbrush, then pushed it about with the paintbrush. To get it to stay put ( not all of it sticks to the glue) I held the dio in the steam made by a kettle 
I have tried baking powder but it went yellow....but I have a new idea for snow...which I will show another time..