The pre-Columbian introduction and dispersal of Algarrobo (Prosopis, Section Algarobia) in the Atacama Desert of northern Chile

Abstract

Archaeological and palaeoecological studies throughout the Americas have documented widespread landscape and environmental transformation during the pre-Columbian era. The highly dynamic Formative (or Neolithic) period in northern Chile (ca. 3700-1550 yr BP) brought about the local establishment of agriculture, introduction of new crops (maize, quinoa, manioc, beans, etc.) along with a major population increase, new emergent villages and technological innovations. Even trees such as the Algarrobos (Prosopis section Algarobia) may have been part of this transformation. Here, we provide evidence that these species were not native to the Atacama Desert of Chile (18-27°S), appearing only in the late Holocene and most likely due to human actions. We assembled a database composed of 41 taxon specific AMS radiocarbon dates from archaeobotanical and palaeoecological records (rodent middens, leaf litter deposits), as well an extensive bibliographical review comprising archaeobotanical, paleoecological, phylogenetic and taxonomic data to evaluate the chronology of introduction and dispersal of these trees. Although Algarrobos could have appeared as early as 4200 yr BP in northernmost Chile, they only became common throughout the Atacama over a thousand years later, during and after the Formative period. Cultural and natural factors likely contributed to its spread and consolidation as a major silvicultural resource.

Fig 1. Prosopis sections seed pods collected by the authors in northern Chile.

Scale bar represents 1 cm. a) cf. Prosopis alba; b) cf. Prosopis flexuosa; c) cf. Prosopis chilensis; d) Prosopis tamarugo.

Fig 2

(A). The modern distribution of Prosopis alba (black dots) and P. flexuosa (red dots) section Algarobia in central South America (GBIF Secretariat: GBIF Backbone Taxonomy. doi:10.15468/39omei. Accessed via http://www.gbif.org/species/5358452 on 2017-04-10; http://www.gbif.org/species/5358528 on 2017-04-10). Note the widespread distribution in NW Argentina, eastern Paraguay and southern Bolivia compared to the distribution in northern Chile. (B) Algarrobos growing in an oasis of the Atacama Desert (C) Archaeological and palaeoecological sites dated in this study, see also S3 Table (1. Lluta 13; 2. Tiliviche 1B; 3. Guatacondo 4. Ramaditas; 5. Quebrada de Maní 6. Caleta Huelén 42; 7. Loa W3; 8. Loa River; 9. Salado River/El Sifón; 10. Salado River/Las Juntas; 11. Chiu Chiu 200; 12. Confluencia 1; 13. Confluencia 2; 14. Chiu Chiu Cementerio; 15. Calar 1; 16. Talabre Viejo; 17. Tarajne; 18. Vegas de Tilocalar; 19. Finca Chañaral).

Fig 3. The intensity of human activities in the Atacama Desert (red curve, from [70]) compared to a summed probability distribution of all AMS radiocarbon dates on Prosopis Algarobia remains from archaeological and paleoecological contexts (dark curve).

The top bar indicates the major cultural periods and paleoclimate variations. Blue bars (orange) represent past wet (dry) climate anomalies. MCA: Medieval Climate Anomaly. LIA: Little ice Age.

Fig 4

(A) A taxon-specific AMS date distribution of the occurrence of Algarrobo remains versus latitude. (B) A taxon-specific AMS date distribution of the occurrence of Algarrobo remains versus elevation.