How do I remove trees from the moat around my fortress?

dwarf-fortress

The moat around my fortress has trees that may be used by monsters to climb inside. Can I get rid of them without removing the water from the moat?


I have found a way: use a ballista!!!

enter image description here

enter image description here

Related

What are the differences between the 4GB and the 250 GB versions of the Xbox 360?
How to stop those mods from downloading when connecting to a server in Call of Duty 4?
Benefits of lycanthropy
Why do pros patrol workers when trying to block buildings?
What happens when I connect Tropico 4 with my Facebook and Twitter accounts?
I'm stuck in Hell, how do I get out?
Where does the game League of Legends take place?
Are the bedlam quests bugged?
Using Mules to ramp up Terran Economy
How can I sell all my vendor trash easily?
When should I mention the Shroud Sabotage, if at all?
Can people have all their blood drained without vampires?