1,166. A Succah on a Wagon, on a Ship, in a Tree...

Hilchos Shofar, Succah v’Lulav 4:5

If a person builds his succah using trees as walls, it is fit for use provided that: the trees are sufficiently strong, or he reinforces them to make them sufficiently strong, that they will not be moved by the wind and; he fills the gaps between the branches with hay and straw, and ties them so that they will not be moved by the wind. This is done because any partition that cannot withstand the average wind is not considered a partition at all.

Hilchos Shofar, Succah v’Lulav 4:6

If a person builds his succah on top of a wagon or on the deck of a ship, it is fit for use and one may enter it on yom tov. If he builds it on a treetop or on a camel's back, it is fit for use but one may not enter it on yom tov because climbing a tree or on an animal is prohibited on yom tov. If some of the walls were man-made and others were trees, we evaluate the succah: one may enter any succah where, if the trees were removed, it could still stand on the basis of the man-made walls alone.