Beavers are strict vegetarians and herbivores, eating only plants and vegetation. They tend to build their homes alongside rivers and the edges of other bodies of water, within close proximity to trees. However, beavers do not simply eat any tree they come upon. The beaver diet includes certain varieties for eating, and others for building their dams and lodges. The beaver diet depends on the season. In the spring and autumn, they will eat both woody and soft flora. In the summer, most of the vegetation they eat will be soft. Trees that make up the beaver diet include bark from willow, cottonwood, aspen, poplar, maple, birch, oak, alder, black cherry, and apple trees. Beavers will gnaw on trees until they fall, and then they clip branches from the resulting logs and add them to their food stash. While beavers will sometimes eat fir, pine, and other conifers, they do not favor them for food. They will often use such trees for dam building, however, or fell them to allow their favorite foods to grow instead. In addition to trees, beavers also eat aquatic plants like lilies, pondweed, and cattails. At the Smithsonians National Zoo, they eat mixed vegetables, rodent chow, leafy greens, and a healthy supply of wood.