Vertex/poly count at right is for entire scene.
Island/ocean: 18612v 35007p
Meshed tree: 159231v 213925p (same for tree with modifiers).
Scene includes one finished tree, and a second, identical except that the modifiers for the fronds are still intact (see 'yucca_palm_preview_viewport.jpg' below). In order to keep viewport performance optimal, an edit mesh modifier was applied to this second tree and then all faces detached. Do this for any new trees created before you use them in any quantity....