Thanks to Chris and Jean for their suggestions. Very helpful.
I had already purged the file when I wrote my post of Dec. 8. Since then I have spent a few days working at or near the event horizon of my computers capabilities. Frequent freezes and bug splats and then 10 minutes of waiting to reload the file.
However, I have managed to run an animation. I had to choose between turning the shadows on and and trees layer off, or all layers on and shadows off. Everything on and my computer would go into full rebellion mode. But I still love it.
I created a video that can be seen here: http://www.aikenresidentialdesign.com/ARD%20modeling%20service.html (bottom of the page).
I think I will follow up on Chris's suggestion to try substituting 2d trees for 3d trees and to see how much of the quality of realism is lost. I have seen some nice 1Mb trees in the warehouse that might be just the thing. If I can create a file that is less temperamental I will be able to fix a lot of imperfections I see in the current video without the high level of frustration of the past few days.
Thanks again.
Karl