Weed Wacker doing a number on your tree trunks
If you buy a 10' lenght of 4" Dia. Thin Wall Sewer Pipe [H/D SKU # A188-499 @ $6.50], it can be cut easly with a hack saw, into 9-12" lenghts to go around the tree trunk. To install, cut one wall of the pipe lenghtwise.
Pipe will curl up on it's self making it a smaller Dia. but that's OK. As the tree trunk grows in size, the pipe guard will easly exspand with the tree's growth.
If you don't like the white color of the pipe, it can be painted with Krylon "Fussion" spray paint made for plastic furniture.
I've installed these guards on the trees at our neighborhood park to keep the City dudes from Wacking the trees so badly.