Sheviis, Chapter 4, Mishnah 6. This Mishnah deals with two matters: how one cuts back vines and reeds during the Sabbatical year, and the tying up of a branch that has come loose from a tree.
Cutting back the ends of vines and cutting reeds in a marsh:
The Mishnah rules: "Hakotzetz es katzos hagefanim" - one who cuts back the ends of the vines, meaning the vine tips - "o hakores kanim b'vitzah" - or one who cuts reeds in a marsh - must cut at a height of at least a tefach above the ground. The reason: if he were to cut lower than that, it would look as though he is preparing the ground for planting.
The opinion of Rabbi Akiva:
Rabbi Akiva says that there is no need to cut specifically a tefach above the ground; rather, one cuts in his usual manner, and with any of the following tools:
An axe.
A sickle - the tool normally used for cutting and for harvesting grain.
A saw.
And likewise any other tool he wishes to use.
In Rabbi Akiva's view, there is no concern here that it will look as though he is improving the ground during the Sabbatical year.
A tree from which a branch has come loose:
A tree from which a branch has come loose - that is, it broke only partially and did not break off completely - may be tied up during the Sabbatical year. The tying is not done so that the branch should reattach itself to the tree permanently, for that is forbidden, but only so that its condition should not deteriorate beyond what it is now: holding the branch up against the tree will prevent it from falling off entirely.
In summary: In this Mishnah we learned three laws: one who cuts back the ends of the vines or cuts reeds in a marsh must leave a tefach above the ground, so that it should not look as though he is preparing the ground for planting; Rabbi Akiva holds that one cuts in his usual manner with an axe, a sickle, a saw, or any tool he wishes, and there is no concern of improving the ground; and a tree from which a branch has come loose may be tied up during the Sabbatical year, not to reattach it permanently, but so that its condition should not deteriorate.