Landscape architect: If the screen between these two areas is to be a hedge, that hedge must be of either hemlocks or Leyland cypress trees. However, Leyland cypress trees cannot be grown this far north. So if the screen is to be a hedge, it will be a hemlock hedge.
The pattern of reasoning in the statement 'Any path along this embankment must be either concrete or stone. But a concrete path cannot be built in this location. So if there is to be a path on the embankment, it will be a stone path' is most similar to that in the landscape architect's argument.