There is a better way to do this than as an extension to the sand set and that is build them just like the trees are..with invisible backgound which is what I will be working on after the new patch goes out the door. As a " tree " type they can be applied over slopes and on ALL other terrains ( grass, grey sand, red sand, red rough sand.....the list is long...they just could not be used in the same hex as trees or orchards but that is hardly a problem
then this could be simulated
or this
