Zoro swung at Dragon Kaidou from the middle of Onigashima there. Accidentally ended up slicing the horn off. Meaning anything within Zoro's "range" - which goes from the centre of Onigashima to the horn on the other side... is fair game to get cut.
That single feat alone places Zoro's range at what? Roughly half the size of Onigashima? Mind you, this was pre-Conquerors btw.
You dont know how large the Adam tree is though, so you can never say for sure whether Zoro will cut it or not.
Though its impressive that only Nasujuro has shown a better "range" feat, pound for pound.