I NEED A HYPOTHESIS A LANDOWNER COULD TEST TO PROVIDE EVIDENCE TO HELP DECIDE WHAT ACTIONS COULD BE TAKEN TO REDUCE EROSION ON A STEEP HILLSIDE?

Answer 1

You could hypothesize:

Junipers planted on a hillside will reduce erosion.

These sites have several other ideas, also.

http://www.laspilitas.com/garden/howto/slope.html

http://landscaping.about.com/od/hillsidelandscaping/Landscaping_on_Steep_Slopes_Hillside_Landscaping.htm