Aspen is the English name for the trembling aspen — the white-trunked tree of cold northern forests whose leaves quiver in the slightest breeze. The town of Aspen, Colorado is also famous, and the name carries a hint of both the tree and the mountain resort.
Aspen as a girl's name is recent, entering the U.S. top 1000 in 2007. Today it sits in the U.S. top 250 — part of the broader return of tree and nature names (Willow, Juniper, Hazel, Magnolia).
Aspen reduces to four — the number of natural rootedness.