hi,
animated model import into ShiVa requires DAE files with bones. blend shapes or vertex modifiers are not supported. I don't know if speedtree supports DAE export, however they should have an FBX exporter, which can easily be converted using either the free autodesk converter, most DCC packages or tools like UU3D.
I looked into speedtree a while back myself, however did not write an integration for monetary, time and license reasons. However IIRC there are a number of ways to integrate speedtree into an engine, and importing models alone was the worst and slowest option available... yes, at the bottom of the page:
http://www.speedtree.com/middleware-integration-sdk.php ... so don't expect to get massive forests with good performance using this method.