回複：boundary dispute

so my question is

1. Can he establish legal ownership (or borderline) by applying mouch
to our plants (if he assumes that we have no objections)? Was this
trespassing if the survey confirms our ownership? Does the survey have
the sole legal right to overwrite his self-made borderline?

YES if you do not objection in certain time (usually many years) depend your stste law.

2. I also wanted to put up a fence on my side along the border after the
survey. I checked with our town hall. They said as long as it is on my side (e.g. 1 or 2 inches from the border) and the fence is
not over 6 feet. I can go ahead and do not need a permit from the town to
do so. So is there any basis the neighbor could sue us? I understand
probably in MA there is no view/sunshine ordinance.
However, the neighbor built a very large house after we moved
in. They basically used up their land and virtually had no
back yard. And our yard effectively becomes their scenary spot. They
fenced everywhere, but not along our common border.
If you have a home owner association, you may get permit from it. Otherwise, go ahead.

3. Can we remove our plants from the border when we
install the fences?

Sure