my white pine tree is starting to turn brown needles. what causes this?
Pine trees shed some of their needles naturally in the fall. If the needle drop is from the interior of the tree and the outer needles are green, this is probably a normal fall occurance. Here is an extension document from Colorado describing this. http://www.ext.colostate.edu/ptlk/2123.html This article also identifies other possible causes such as drought, pesticide damage and soil compaction among others.