Using Design options as for isolating selections.

Placing elements in a design option isolates them from the rest. This makes it easy to select and move them around without accidentally modifying other elements. In this example all trees are on the same layer, only the larger trees are in a design option. By turning the design option on and off you can select all the trees or just the larger trees.

With this setup, it is also possible to select part of the large trees (different the with the selection set pallet). This speeds up the workflow.