Responsa for Bava Batra 50:13
רבי יוסי אומר אע"פ שהבור קודמת לאילן לא יקוץ שזה חופר בתוך שלו וזה נוטע בתוך שלו: אמר רב יהודה אמר שמואל הלכה כרבי יוסי אמר רב אשי כי הואן בי רב כהנא הוה אמרינן מודי ר' יוסי בגירי דידיה
<b><i>MISHNAH</i></b>. A TREE MUST BE KEPT AWAY FROM A PIT [IN A NEIGHBOUR' S FIELD] TWENTY-FIVE CUBITS — A SYCAMORE OR A CAROB FIFTY CUBITS;<span class="x" onmousemove="('comment',' Because the roots spread to a great distance. ');"><sup>22</sup></span> IT MAKES NO DIFFERENCE WHETHER THE TREE IS ON HIGHER OR LOWER GROUND OR ON A LEVEL WITH THE PIT. IF THE PIT WAS THERE FIRST, THE OWNER CAN HAVE THE TREE CUT DOWN ON GIVING COMPENSATION. IF THE TREE WAS THERE FIRST, HE CAN NOT HAVE IT CUT DOWN. IF THERE IS A DOUBT WHICH WAS THERE FIRST, HE CANNOT HAVE IT CUT DOWN. R. JOSE, HOWEVER, SAYS THAT EVEN IF THE PIT WAS THERE BEFORE THE TREE THE OWNER CANNOT HAVE THE TREE CUT DOWN, BECAUSE THIS ONE DIGS IN HIS PROPERTY, THE OTHER PLANTS IN HIS.
Teshuvot Maharam
A. Those parts of the beams which extended into A's portion belonged to him exclusively, and he had a right to cut them off, especially since the intervening wall belonged to him. Although the act of sawing and chopping weakened B's and C's structures, since the extension of the beams into A's room served no useful purpose to B and C, and because of their unnecessary weight were even detrimental, A had a right to cut them off. In any event, B and C are not entitled to any compensation for their loss, now that the act has been done.
SOURCES: Am II, 198.