Patagonia Desert

• Category: Desert Biomes.
• Geographic Location: South America.
• Summary: One of the world’s most outstanding examples of a rain-shadow desert lies at the narrow southern tip of South America, where geography seems to rule out any but a cool and moist climate.

The Patagonia Desert lies in the southern conical tip of South America, also known as Tierra del Fuego, or land of the fire. The desert is considered to be the largest desert in the Americas, and the seventh-largest desert in the world. The Andes Mountains form a barrier immediately to the west, effectively shutting off the moist westerly winds blowing in from the South Pacific; this creates the rain-shadow effect. Half or more of this desert lies within only 200 miles (322 kilometers) of either the Atlantic or Pacific Oceans. Because of improper land use, more than 90 percent of Patagonian soils are degraded to some degree. In addition, severe desertification affects much of the fringe areas of the core desert region here.

Flora

Patagonia is largely covered by treeless shrub and grass steppes that give way to dwarf-shrub semi-deserts in the drier areas of the central plateaus here. Vegetation is characterized by the dominance of xerophytes, plants that have evolved remarkable adaptations to cope with severe water deficits. Shrubs, for example, have either very small, sclerophyllous (hard and waxy) leaves with abundant glandular hairs or leaves with thick cuticles. Many species have dwarf cushion growth, another means of conserving moisture.

Grasses commonly have leaves with thick cuticles, convoluted laminae, and bunch growth habits, and with fairly large accumulations of dead biomass that help shield the grass from transpiration.

Blended in the more arid steppe landscapes are small areas associated with rivers or permanent water sources, with more mesic (moisture-adapted) plant communities comprising mostly grasses, sedges, and rushes. These are referred to as riparian meadows. Although they account for a small proportion of the total area, they play a key role in livestock production, and in many cases suffer most from the effects of bad land management, specifically overgrazing.

Shrub steppes occur in transition areas between the grass steppes and the semi-deserts. Semi-deserts and shrub steppes exhibit similar latitudinal extents. The steppe grassland usually is found in areas that are less prone to moisture in the form of rain or groundwater. Steppe vegetation is well suited to this drier climate, and the grass generally is shorter than that on prairie grasslands. Steppes are virtually semiarid deserts in the making—they are highly threatened by overgrazing, and highly sensitive to global warming, with desertification advancing as temperatures and evaporation rates increase.

Together, both variants of semi-desert cover 22 percent of the region, with plant communities of low diversity, including on average 19 plant species. Dwarf shrubs with cushion habits are typical of this type of vegetation. Nassauvia glomerulosa, N. ulicina,and Chuquiraga aurea are dominant, accompanied by Chuquiraga kingii, Brachyclados caespitosus,and Perezia lanigera. Grasses, such as Stipa humilis, S. ibarii, and S. ameghinoi; and shrubs, such as Chuquiraga avellanedae, Schinus polygamus,and Lycium chilense, are secondary types in semi-desert plant communities.

Dwarf shrubs, such as Azorella caespitosa, Mullinum microphyllum, and Frankeniaspecies; grasses, such as Poa dusenii, P. ligularis, and (less frequently) Stipa neaei; and shrubs, such as Junellia tridens, occur in clumps in ancient depressions and along natural drainage networks.

Patagonia’s deserts and semi-deserts have a quite different non-gramineous (non-grass-family) flora from those in the Northern Hemisphere. Stipa and Festuca are common to the semi-deserts of all three continents, but the shrubs and forbs of Patagonia are mostly cushion plants belonging to the Asteraceae, Verbenaceae, and Rubiaceae families. The fact that these types of plants are favored here may be related to the fact that the strong, nearly constant winds create a large amount of transpiration stress. These plants have adapted to this harsh weather by having thicker cuticles and smaller stomatas that help prevent loss of water, which means less transpiration; they also have adapted photosynthesis cycles that allow them to flourish in this environment. The taxonomic uniqueness, however, probably is related to the distance of this tip of the South American continent from the rest of the world’s land masses.

Fauna

During most of the Tertiary Period, there was an absence of land connections between South America and other continents. Thus, its fauna evolved in isolation, making it much more diverse than at present. Animals evolved that were unique to the continent, including giant sloths, tank-like glyptodonts, and saber-tooth marsupials. Because the isolation of this area was incomplete, however, caviomorphs and marsupials arrived during the Late Eocene. The greatest exchange seems to have taken place around 5 million years ago with the emergence of the land now known as Central America, which allowed for the fauna in North and South America to mingle. The Panamanian land bridge was fully in place 3 million years ago, and the interchange of fauna has continued to the present.

Animal life on the Patagonian steppe is comprised of grazing mammals and a wide variety of burrowing mammals such as ground squirrels and ferrets. Patagonia is left today mainly with ungulates, guanacos, and some rodents, dogs, and cats.

Birds may fill part of the niches that mammals have in similar habitats on other continents. The large flightless bird, the rhea, is a browser; ground-dwelling parrots are major carnivores. The heteromyids—long-tailed, nocturnal mice species—that are so abundant in the temperate deserts of the Northern Hemisphere are lacking in Patagonia, but are replaced by bird species and a few caviomorphs, a specialized clade of rodents. The avifauna of the driest portions of Patagonia include the large, ground-feeding bird family Tinamus.

Threats

The area remains sparsely populated, but mining for gas, coal, oil, and other natural resources is changing the region. Only about 3 percent of the area is protected, which is about 6,177,635 acres (2,500,000 hectares). Oil mining is particularly taxing on resources. However, this practice is somewhat restricted. Overgrazing has been a long-standing threat to plants, soils, and animal habitats in some areas of the Patagonia Desert biome. Over the past few decades, 35 percent of the arid and semi-arid steppes have transformed into deserts, due mostly to overgrazing.

The enduring effects of climate change in this region of South America are difficult to model due to countervailing variables such as potential changes in oceanic currents, Antarctic glacial melt rates, air temperature and pressure regimes, and uncertainty over long-term wind patterns. However, despite lacking projections, farmers, conservationists, and activists have worked together to alleviate practices, such as overgrazing, that are known to deteriorate the land and influence desertification.

Bibliography

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“Patagonian Steppe.” IUCN, 8 July 2010, iucn.org/content/patagonian-steppe. Accessed 25 Oct. 2024.

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