The Gran Chaco is a vast lowland plain stretching across parts of Argentina, Paraguay, and Bolivia, covering roughly 1 million square kilometers. It is the third largest biome in South America, after the Amazon and the Cerrado, and one of the continent’s most ecologically significant yet threatened landscapes. Despite its size, it remains relatively unknown outside the region, overshadowed by the Amazon even as it faces some of the fastest deforestation rates on Earth.
Where the Gran Chaco Is
The Chaco sprawls across the interior of South America, west of the Paraguay and Paraná rivers. The majority of the land falls within northern Argentina, which contains the largest share. Western Paraguay holds the next biggest portion, a sparsely populated area known as the Chaco Boreal. A smaller section extends into southeastern Bolivia, with a sliver reaching into parts of southwestern Brazil in some definitions.
The region is flat to gently rolling, with no significant mountain ranges. Rivers cut through the landscape but many are seasonal, drying up for months at a time. This flatness and isolation have kept the Chaco thinly populated compared to surrounding areas, though that has changed rapidly in recent decades as agriculture has pushed deeper into the forest.
Climate and Sub-Regions
The Chaco is hot. Summer temperatures regularly exceed 40°C (104°F), with wide daily swings that grow more extreme the farther west you go. Winters are mild overall, but occasional frosts hit during the dry season in June and July. Rainfall follows a sharp east-to-west gradient: the eastern portions receive enough rain to support lusher vegetation, while the western interior is markedly drier and more seasonal.
This rainfall gradient creates two distinct sub-regions. The Humid Chaco, in the east, receives precipitation more evenly throughout the year. It supports marshlands, palm savannas, and gallery forests along rivers. The Dry Chaco, covering the western interior, is semi-arid, dominated by thorny scrubland and drought-adapted trees. A third zone, the Sierra Chaco, occupies higher ground along the foothills of the Andes. Each sub-region has its own soil types, plant communities, and levels of species found nowhere else.
Wildlife and Plant Life
The Chaco’s dry forests and savannas support a surprising range of species for a semi-arid environment. The most famous resident is the Chacoan peccary, a pig-like mammal that scientists knew only from fossils until a living population was discovered in the Paraguayan Chaco in 1975. Giant armadillos, jaguars, maned wolves, and several species of large cat also inhabit the region, though their populations are under pressure from habitat loss.
The signature trees of the Chaco are the quebrachos, whose name translates roughly to “axe-breaker,” a reference to their extraordinarily hard wood. These slow-growing trees were historically logged heavily for tannin extraction and railroad ties. The legume family (Fabaceae) is especially well represented across the Chaco, serving as one of the best indicators of the region’s overall plant diversity and patterns of species unique to specific areas.
UNESCO has designated a large biosphere reserve in the Paraguayan Chaco, encompassing several national parks: Defensores del Chaco, Médanos del Chaco, and Teniente Agripino Enciso, among other protected areas. The Rio Negro National Park, within the reserve’s core, is also a Ramsar Site, recognized since 1995 for its importance as a wetland ecosystem.
Indigenous Peoples of the Chaco
The Gran Chaco is home to approximately 300,000 indigenous people as of 2018, belonging to a remarkable diversity of ethnic and linguistic groups. Researchers have identified at least six major language families in the region: Mataco-Mataguayo (including the Wichí, Chorote, and Nivaclé), Guaicurú (including the Toba or Qom, Pilagá, and Mocoví), Zamuco (including the Ayoreo), Lengua-Maskoy, Lule-Vilela, and Tupí-Guaraní (including the Chiriguano and Isoseño-Guaraní).
Many of these groups historically lived as hunter-gatherers and fishers, adapted to the Chaco’s harsh seasonal cycles. Today, indigenous communities face ongoing challenges related to land rights, deforestation encroaching on their territories, and limited access to services. The Ayoreo of Paraguay are notable as one of the last indigenous groups in South America with members still living in voluntary isolation from outside contact.
The Chaco War
The Gran Chaco was the site of South America’s deadliest 20th-century conflict. For over a century, Bolivia and Paraguay (along with Argentina) had claimed overlapping portions of the Chaco Boreal, the northern section of the plain. Much of the confusion traced back to inconsistent land surveys conducted during the Spanish colonial era, and for decades the dispute played out on paper, with conflicting maps published by each nation.
Tensions escalated in the late 1800s when oil prospecting and foreign investment entered the region, raising the economic stakes. For Bolivia, which had lost its Pacific coastline to Chile in an earlier war, controlling the Chaco offered a route to Atlantic-bound rivers. For Paraguay, the territory was a matter of national survival. Fighting broke out in 1932 and lasted three brutal years. An armistice was reached in 1935, with a final peace treaty signed in 1938. Paraguay was granted nearly all of the disputed territory, while Bolivia received access to rivers leading to the Atlantic coast.
Deforestation and Agricultural Expansion
The Gran Chaco is now one of the world’s most active deforestation frontiers. Since the 1980s, rising global commodity prices, favorable farming conditions, cheap land, and the entry of international agribusinesses have driven rapid clearing of forest for cattle ranching and soybean cultivation. Ironically, increased forest protection in the Amazon may have redirected some agricultural pressure onto the Chaco and other dry forest regions.
The drivers of deforestation vary by country. In the Paraguayan Chaco, nearly all forest clearing is for cattle pasture. In Argentina, cattle ranching is also the dominant force, but soybean fields account for a significant share of converted land. Research published in Global Environmental Change found that soybean production acts as a direct driver of deforestation specifically in the Argentine Chaco, while cattle ranching is significantly associated with forest loss across all three countries. Globally surging demand for soybeans appears to be the overarching force behind the region’s transformation.
The numbers are stark. In 2024 alone, the Argentine province of Chaco lost 50,000 hectares of natural forest, producing an estimated 11 million metric tons of CO₂ emissions. Between 2001 and 2024, 92% of tree cover loss in that province resulted from outright deforestation rather than natural causes. Permanent agriculture accounted for 940,000 hectares of that loss over the period.
Conservation efforts exist but remain outpaced by clearing. Argentina passed a national forest law in 2007 that categorizes forests by conservation priority, but enforcement has been uneven. Protected areas like the Paraguayan biosphere reserve cover important habitat, yet vast stretches of the Chaco remain unprotected and increasingly fragmented by roads, fences, and fields expanding into what was, until very recently, continuous dry forest.