Question
We have three large pine trees about eight feet from where the house's main drain runs.  There are also large maples along the city line.  I am wondering which would be the culprits in having caused possible damage to the drain which is over 40 years old and joined in iron pieces as opposed to one long pipe of PVC or other such material?  Haven't confirmed damage yet but basement drain backed up the other day. Trying to establish whether it's city trees or ours.

Answer
I would think the maples are the problem since they have a dense roots system while the pines roots are larger and also the pine has a tap root. Maples have been known to clog sewer lines with their roots. The only real way to tell which is doing the clogging is to dig the pipe up and id the roots. The pine roots will have a sticky like sap in them.