A great subject. What I like is it looks like you make it in full scale, realistic proportions.
Traveller1865 wrote:toothpicks might be too small, tried barbeque pins and then twigs but it just fell apart
I would suggest twigs because those are most lively.
Toothpicks and barbeque pins are sterile, too straight, even for pinewood and fir, unless you threat them afterwards with a paste like acrylics or white glue and fine powder to roughen it a littlebit.
If it all falls apart, try to glue twigs or picks on a styrofoam base. This base can be removed afterwards when all glue has dried, or implant the foam base into the surface of your diorama.
Don't be impatient!