Insert in your scene, a Surface Réplicator, which is in the drop-down Replicator tool (the second icon)
You should now have an emty bounding box in the scene, as the capture bellow shows. Don't worry where it is located in the scene.
Now for the most interesting part : how the replicator works.
Lets take a closer look to the Carrara scene tree in the properties tray (NOTE: Not the palmtree

) on the screen capture shown bellow. What can we see? A surface Replicator (highlighted), a Plant and a Terrain, our three require elements.
To generate the duplication, we have to give to the replicator what must be replicated: the Palmtree.
For this operation, pick and drag the Plant (red arrows) on to the Surface Replicator line. You should have what can be see in the right screen capture bellow, a kind of Hierarchy in the red circle.
Double click on the Surface Replicator line in the scene tree, this will allow us to edit its parameters. The surface replicator modeling room will open as the screen capture shows bellow.
Click the "Choose" button in the "Source Object" section, as shown in the red circle above. A new window should open, as the screen capture bellow presents. Select the Terrain and hit OK
Go back to the Assembly room : A lot of empty bounding boxes appear: They are the replicated trees. You can see all the trees, by choosing in the property tray the display mode, but it is best to use the bounding boxes.
Another problem is that all the boxes are align along the ground (the normal) and the worst is we have Palmtrees in the water !
Time to see how to correct that!