The Greater Yellowstone Ecosystem. Description of an ecosystem's size, boundaries, and characteristics can vary greatly. At 3,437.5 square miles (8,903 km2),Yellowstone National Park forms the core of the Greater Yellowstone Ecosystem—one of the largest nearly intact temperate-zone ecosystems on Earth. Greater Yellowstone’s diversity of natural wealth includes the hydrothermal features, wildlife, vegetation, lakes, and geologic wonders like the Grand Canyon of the Yellowstone River.