Ash tree and Red ash

Ash tree noun - Any of various deciduous pinnate-leaved ornamental or timber trees of the genus Fraxinus.

Red ash and ash tree are semantically related. In some cases you can replace phrase "Red ash" with "Ash tree", this phrases are similar.

Red ash noun - Smallish American tree with velvety branchlets and lower leaf surfaces.

Ash tree and red ash are semantically related. You can use "Ash tree" instead a noun phrase "Red ash".