Trees fell by beaver, in Grand Teton National Park, Wyoming. Like all rodents, beaver incisors grow continuously so they won't be worn out, and their enamel contains iron (giving them an orange/rust color) to be more resilient against acid wear than the teeth of other mammals. While they may be pests in some areas, beavers are a natural part of the ecosystem here. Not only do they create vital wetlands for migratory birds (something that is increasingly rare thanks to humans), but it's also a stable water source for wildlife. Cutting the larger trees lets more sunlight reach the forest floor, allowing for new growth, which provides food and cover for wildlife. They're an absolutely fascinating animal, and I didn't even mention how intelligent their dam structure is!