Glacier is part of a large preserved ecosystem collectively known as the "Crown of the Continent Ecosystem", all of which is a primarily untouched wilderness of a pristine quality. Virtually all the plants and animals which existed at the time European explorers first entered the region are present in the park today.
A total of over 1,132 plant species have been identified parkwide. The predominantly coniferous forest is home to various species of trees such as the Engelmann spruce, Douglas fir, subalpine fir, limber pine and western larch, which is a deciduous conifer, producing cones but losing its needles each fall. Cottonwood and aspen are the more common deciduous trees and are found at lower elevations, usually along lakes and streams. The timberline on the eastern side of the park is almost 800 ft (244 m) lower than on the western side of the Continental Divide, due to exposure to the colder winds and weather of the Great Plains. West of the Continental Divide, the forest receives more moisture and is more protected from the winter, resulting in a more densely populated forest with taller trees. Above the forested valleys and mountain slopes, alpine tundra conditions prevail, with grasses and small plants eking out an existence in a region that enjoys as little as three months without snow cover. Thirty species of plants are found only in the park and surrounding national forests.[86] Beargrass, a tall flowering plant, is commonly found near moisture sources, and is relatively widespread during July and August. Wildflowers such as monkeyflower, glacier lily, fireweed, balsamroot and Indian paintbrush are also common.