State foresters Tuesday recorded the first deaths of beech trees from a disease that just arrived in the state four years ago and is now present in all 16 counties. Scientists say beech leaf disease could decimate a species that’s common in Maine woods and an important food source for wildlife. An invasive microscopic roundworm called a nematode causes the disease, which was first detected in Ohio in 2012 and has since rapidly spread north and east. Aaron Bergdahl, a forest pathologist with the Maine Forest Service, said while checking a monitoring plot in the MidCoast Tuesday morning, scientists made an unfortunate discovery: the first tree deaths from the disease. …Bergdahl said there are currently no practical forest-level treatments for beech leaf disease, but there are for homeowners.