In Europe it's not so much that years get warmer, but that winters are less cold. I expect many parts of the U.S. are similar. Frost would typically kill a lot

In Europe it's not so much that years get warmer, but that winters are less cold. I expect many parts of the U.S. are similar. Frost would typically kill a lot of species, except a few that are specialized to withstand it. Withstanding frost is often a trade-off. So if this threat is removed, many native species have a disadvantage. (I'm beekeeper and many of the threats to native honeybees are because (European) honeybees put a lot of energy into preparation for long periods of frost,while their adversaries don't do that. It's a bit like the story of the Ant and the Grasshopper. Only now it turns out the grasshopper was right all along, in not caring)