Hi eric, I don't think that most rendering programs have much of a focus on making it easy to include vegetation... So you may not really have a whole lot of other options really.

One thing that could fit though is Vue by E-on software: http://www.e-onsoftware.com/products/solutions/?page=architecture

That particular program has a lot of focus on generating natural scenes and vegetation, if nice looking trees that can be set up easily is a big priority then you might want to check that particular one out.

- Michael