Artstation - Introduction to Houdini - Procedural Scattering & Houdini in UE4
https://www.artstation.com/learning/courses/rv9/introduction-to-houdini-procedural-scattering-houdini-in-ue4

In this course, Kem Yaralioglu shows how to prepare and use HDA inside UE4. He covers the scattering node and how to expose parameters that can then be updated in-editor. This will not necessarily cover how to create a production level landscape but will cover how to use the scatter node and how HDA’s work.