I was about to post this as a response in the Dogwood Pest thread, but decided it should have its own thread:
I do worry whether we will end up with any trees left. Along with dutch elm disease, chestnut blight, emerald ash borer and anthracnose (which affects several varieties of trees), we are currently fighting:
hemlock wooly adelgid- an insect that is rapidly spreading and destroying eastern and Carolina hemlocks
balsam wooly adelgid - relative that attacks balsam and Fraser fir trees
Asian longhorn beetle- a truly terrifying one, since it attacks many different hardwood trees
beech bark disease - introduced disease threatening American beech trees
mountain pine beetle - This one is actually a native beetle, unlike most of these pests. When things are in balance, "these insects play an important role in the life of a forest, attacking old or weakened trees, and speeding development of a younger forest. However, unusually hot, dry summers and mild winters throughout the region during the last few years, along with forests filled with mature lodgepole pine, have led to an unprecedented epidemic. It may be the largest forest insect blight ever seen in North America. Climate change has contributed to the size and severity of the outbreak, and the outbreak itself may, with similar infestations, have significant effects on the capability of northern forests to remove greenhouse gas (CO2) from the atmosphere. " (wiki - https://en.wikipedia.org/wiki/Mountain_pine_beetle )
white pine blister rust - non-native fungal disease, rapidly wiping out western white pine forests. introduced to North America around the turn of the twentieth century. Since its introduction, it has spread to 38 states and caused substantial damage and mortality
sudden oak death - in california and oregon, but spreading and affects a wide variety of trees; like many of these, no known cure
European gypsy moth - found from Vermont to North Carolina and from New York and New Jersey to OH, KY, MI, WI. This moth is a significant pest because the caterpillars have voracious appetites for more than 300 species of trees and shrubs, posing a danger to North America's forests. The caterpillars defoliate trees, leaving trees vulnerable to diseases and other pests and can eventually kill the tree.
And of course you can't just remove one kind of tree from a forest. Every time one of these goes, there are cascading effects on associated plant and animal communities.
When we think of endangered species, we don't normally think of trees, but they may be the weakest link and the most critical, since they play such an important role in sequestering carbon.