Generally people are afraid that drycha is using the power of the leyline for something. Tapping into a leyline held a dwarf hold in the warp for several hundred years and they tried to be subtle about it. If we know for sure the leyline is disconnected in the forest we can plan our attack around disrupting the ritual it is being used in.
"Kill the one doing them and they tend to end," Regimand advises helpfully.
Problem solved.
But on a more serious note, actually having Ice Witches on our team would really help shut down any funny business with the waystone, mainly because they are the ones with the permissions and secrets to actually mess with them.