The HBRA is home to several ecosystems, including prairie and oak savanna.  So . . .  What's the difference?  Simply put, a prairie has no trees, a savanna has trees.

A prairie is a grassland with no trees.  A savanna is a grassland with scattered trees (in the HBRA's case, Oregon White Oak a.k.a. Garry Oak), often with a classic spreading form, covering up to 25% of its area.

The HBRA is home to one of the largest remaining contiguous oak savanna habitats in the entire Willamette Valley.  The oak savanna ecosystem was much more widespread in the valley prior to the arrival of European settlers.