Ash tree and Black ash

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

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

Black ash noun - Vigorous spreading North American tree having dark brown heavy wood; leaves turn gold in autumn.

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