Pilcomayo River and to the west of the Paraguay River). Eventually, Argentine Foreign Minister Carlos Saavedra Lamas mediated a ceasefire and subsequent treaty signed in 1938, which gave Paraguay three-quarters of the Chaco Boreal and gave Bolivia a corridor to the Paraguay River with the ability to use the Puerto Casado and the right to construct their own port. No oil was found in the region until 2012 when Paraguayan President Federico Franco announced the discovery of oil in the area of the Pirity river. Mennonites immigrated into the Paraguayan part of the region from Canada in the 1920s; more came from the USSR in the 1930s and immediately following World War II. These immigrants created some of the largest and most prosperous municipalities in the deep Gran Chaco. The region is home to over 9 million people, divided about evenly among Argentina, Bolivia, and Brazil, and including around 100,000 in Paraguay. The area remains relatively underdeveloped, In the 1960s, the Paraguayan authorities constructed the Trans-Chaco Highway and the Argentine National Highway Directorate, National Routes 16 and 81, in an effort to encourage access and development. All three highways extend about from east to west and are now completely paved, as is a network of nine Brazilian highways in Mato Grosso do Sul state. Flora The Gran Chaco has some of the highest temperatures on the continent. It has high biodiversity, containing around 3,400 plant species, 500 birds, 150 mammals, and 220 reptiles and amphibians. The floral characteristics of the Gran Chaco are varied given the large geographical span of the region. The dominant vegetative structure is xerophytic deciduous forests with multiple layers, including a canopy (trees), subcanopy, shrub layer, and herbaceous layer. Ecosystems include riverine forests, wetlands, savannas, and cactus stands, as well. At higher elevations of the eastern zone of the Humid Chaco, mature forests transition from the wet forests of southern Brazil. These woodlands are dominated by canopy trees such as Handroanthus impetiginosus and characterized by frequent lianas and epiphytes. This declines to seasonally flooded forests, at lower elevations, that are dominated by Schinopsis spp., a common plains tree genus often harvested for its tannin content and dense wood. The understory comprises bromeliad and cactus species, as well as hardy shrubs such as Schinus fasciculata. These lower areas lack lianas, but have abundant epiphytic species such as Tillandsia. The river systems that flow through the area, such