Is my tree dying?
Thank you for contacting us with your question. I'm sorry about the damage to your trees, healthy quaking aspen are so beautiful. I know that the utility folks are required to maintain clearance around power lines for safety reasons, but that doesn't mean the pruning is any less disruptive to the plant.
Based on your photos, I would say the dripping of pitch is the normal response to a severe pruning, and by itself doesn't mean the tree is dying. The black color looks like it may be something called sooty mold, which is growing on the pitch. It should not harm the tree. I've linked to more information about sooty mold:http://hortsense.cahnrs.wsu.edu/Public/FactsheetWeb.aspx?ProblemId=331
Aspen trees are prone to pests, and so there could be an insect or disease that shows up in the near future. It's hard to say whether the pruning wounds will make that more likely or not, but be on the look out for symptoms such sawdust on the trunk or on the ground around the base, as this is a sign of borers. Leaf or twig blights will cause the leaves or twigs to turn black and sometimes curl up. I've attached another link to more information about diseases of trees in this family (which includes Poplars and Cottonwood): http://hortsense.cahnrs.wsu.edu/Search/MainMenuWithFactSheet.aspx?CategoryId=1&SubCatId=5&Pl...
In our area, the individual trunks of aspen trees often have a shorter life span, but the root system will usually survive to send up new shoots to replace what has died. In some cases, this can cause problems as the shoots will appear in lawns, or cross property lines. If your tree has some space to spread out, you can allow some of the shoots to grow (hopefully away from the power lines) and remove any that are growing in the wrong place.
I hope this helps answer your question, let me know if you have any more, or if I've been confusing at all. Best of luck with your tree!