At the transition zone between the arid steppe of Argentine Patagonia and the temperate southern beech forests of Chilean Patagonia, the future Patagonia National Park contains an array of ecosystems including grasslands, mountains, southern beech forests, and wetlands. Thanks to this range of habitats, biodiversity can thrive. Species roam freely from habitat to habitat, adapting to changing temperatures with the availability of vertical gradients.
The dry steppe of Argentine Patagonia is a characterized by minimal rainfall (less than 150 millimeters annually), cold, dry winds, and sandy soil. The Andes Mountains block moisture from flowing west, creating this arid area only 200 miles from the ocean. A number of tough plants have been able to adapt to this harsh environment, such as shrubs like calafete, quilembay and yaoyín and tuft grasses like flechilla and coirón poa. These grasslands support hardy animals such as the burrowing owl, the gray fox, tuco-tuco, mara, armadillos, various eagle and hawk species and keystone predators like the puma. A wider range of animals thrive in the more habitable outskirts of the desert and around ephemeral lakes formed from the Andes' runoff, where trees and more nutritious aqueous grasses can grow.
Moving west and climbing the vertical gradient of the Andes Mountains, the flora and fauna changes notably. The landscape begins to transform into forests, which consists mostly of three species in the southern beech (Nothofagus) genus: lenga, ñire, and coiyue. Rainfall can reach 4,000 millimeters per year, generating dense forests, full of nutrients from high leaf litter. These forests act as home to 370 vascular plant genera, which are vital to the survival of the surrounding fauna. Some significant mammals include the endangered huemul deer, the puma, the red fox, and various species of bats. The forests of the future Patagonia National Park contain a high diversity of bird species and a range of amphibians and reptiles.
Throughout Patagonia, the guanaco, a large camelid that is a wild relative of the llama, is the most abundant herbivore. It feeds on 75% of all plant species in the Patagonian steppe. The guanaco acts as a keystone species: they prevent domination of grass species, act as great dispersers and fertilizers, and have high reproductive rates providing food for neighboring carnivores, especially pumas.
Although the park lies on the eastern side of the Andes, its glacier-fed streams and rivers run towards the Pacific Ocean. Their turquoise blue water is some of the purest in the world, and is home to substantial populations of native fish such as perca (percichthys trucha), pejerrey patagonico (patagonina hatcheri) and puyen. Atlantic salmon, brook, brown and rainbow trout have been introduced to the area.