Perhaps "a stand of trees" might apply, depending on the nature of the particular collection of trees/forest being described.
"Stand" applies to any crop or planting that grows vertically (e.g. "stands") according to the OED.
Also, as a forestry term:
stand - a group of forest trees of sufficiently uniform species composition, age, and condition to be considered a homogeneous unit for management purposes.
(source:
http://www.dnr.state.md.us/forests/gloss.html#s)