Ask Mr. Smarty Plants

This Mr. Smarty Plants suggests that you look carefully at the trunks of your young Acacia farnesiana (Huisache) trees.  A buck or bucks (male deer) managed to girdle (damage the bark all the way around) the trunk of my young huisache when they were rubbing their heads to remove the velvet from their newly-grown antlers last year.  The girdling caused the phloem (food transport) and perhaps the xylem (water transport) to be destroyed between the area of the tree above the girdling and the roots thus killing the tree.  Many (maybe most) neighborhoods in Austin have resident deer.  If you do, that may explain your dead huisache trees.  In places where deer live it is a good idea to protect the trunks of young trees by surrounding them with some sort of wire protection.  The YouTube video,  Installing deer protection on young trees, shows a simple, inexpensive way to do this yourself using hardware cloth.  There are other methods using a variety of materials.  Check with your local nursery or hardware store for other options.  You can see photos of a young girdled tree on TreeBoss.

As it turned out, my huisache wasn't completely dead since, after it lost all its leaves, it has now sprouted new growth from the roots and the trunk below the girdling.  It looks as if it is now going to be a huisache shrub, not a tree.  If your young trees were girdled, perhaps they will resprout from the roots, also.