By the Bais Hora'ah
Reuven and Shimon are neighbors. Shimon built a stone wall on the property line. Reuven’s tree’s roots crossed under the property line and are damaging Shimon’s wall. Shimon asked Reuven to remove the roots. Reuven refused and told Shimon that if the roots are bothering him, he should take care of it himself.
Q: Who is responsible to make arrangements and pay to have the damaging roots removed?
A: Shulchan Aruch (155: 32, 26) rules that one may plant a tree on his own property even though it is close to his neighbor’s water pit. Even if the neighbor protests out of concern that the tree’s roots will eventually damage his water pit, it is permitted. The reason is that he planted on his own property and at that time the tree was not damaging the neighbor’s water pit. The damage occurred later when the tree grew and expanded. It is therefore the neighbor who must protect himself from damage, and he may, at his own expense, trim the roots that are damaging his water pit.
For this reason, if the branches of one person’s tree extend over the property line and prevent his neighbor from building his sukkah (O.C. 626:1), the neighbor may not demand that the tree owner trim his tree. Since the tree is located on the owner’s property and the damage is the result of the tree’s growth, he is not liable. The neighbor, however, may trim those branches that cross the property line and prevent him from building his sukkah.
What requires consideration in your case is the Rosh’s opinion that when the following three factors are present, the tree owner is obligated to stop his tree from damaging a neighbor’s property: 1) The damaged party cannot easily remove the damaging tree; 2) The impact on the damaged party’s use of his property will be continuous, and 3) The damage is significant (C.M. 155:20; see also Nesivos 3). Accordingly, if the roots of Reuven’s tree will cause significant damage to Shimon’s house, Reuven is obligated to stop his tree from doing so. The general ruling that exempts the tree owner of responsibility is limited to damage that is minimal (Chazon Ish, B.B. 14:13).
If roots from a person’s tree penetrate a neighbor’s sewer system, and the only way to prevent further damage is to remove the tree altogether, the tree owner must remove his tree. When the damage is not that extensive and could be prevented by trimming the roots from time to time rather than cutting down the entire tree, the tree owner cannot be forced to remove his tree or even trim the damaging roots (Mishkan Shalom, p. 166).
The above relates to whoever is actually responsible to trim the tree, but if the expense to cut down the tree will be great and the tree owner was not negligent, the owner is not responsible and the damaged party will have to bear those expenses (Mishkan Shalom, p. 123, 170). However, if while planting the tree the owner realized that the tree will cause his neighbor damage and it would be costly to prevent the damage, the tree owner is responsible for paying for the tree’s removal (ibid., and Mishpetei Hachoshen, p. 184).
In your circumstance, the matter is subject to the discretion of the Dayanim as to whether they consider the damage extensive and whether it will have an ongoing impact on Shimon’s use of his property.