"Careful, the trees!"
Translation:Achtung, die Bäume!
sorgfältig is wrong in this context. Sorgfältig would be used with something like "He carefully folded the clothes", or some other task where you have to be really thorough and pay attention to every little detail. In this case however, it's an exclamation: "Careful, the trees!" suggests that you want the other guy to watch where he's going/driving, because there are trees everywhere and he's kinda reckless. In this context, "Achtung", "Pass auf" or "Vorsicht" would be what you might say. But definitely not "Sorgfältig".
"Vorsicht, die Baeume": is the better translation here. IMHO 'Careful' implies, to be careful on your way through the woods, the trees are getting closer and closer and you are being warned to avoid them.
Whereas "Achtung!" means attention, pay more attention on how you are driving, you are coming very close to the trees!
It is nearly the same, but not the same!