Photo Three - Similar to the image posted above, toffee-apple fencing and a resin sack. The nails are just slivers of plastic rod, superglued to the distressed sticks.
Photo Four - A single tall tree which started life as a cheap Christmas decoration which has been cut and chopped about then had an extended trunk modelled with Milliput and once again mounted on to a small oval of 3mm MDF. The method I use to get this random tree shape is to place the tree in an oven (low heat), the foam is then partially melted to give the organic shape - please note that extreme care is needed to ensure that the effect is not too much. You also need a very (very) understanding Wife!
Photo Five - As above but with dried wood chips painted as stones/boulders on the base. Please note how the character of the tree can be changed by extending the trunk or tilting it.
The more rounded trees in the distance are cheap (very cheap) railway modelling trees, which are in fact lumps of dried and coloured sawdust mounted in a similar way to the evergreen trees. I have had these tree models for some time and use them for many different games and genres.