Critically-endangered South American forests were man-made
Release Date 18 May 2018
Critically endangered South American forests thought to be the result of climate change were actually created by ancient communities, archaeologists have found.
Huge swathes of land in Chile, Brazil and Argentina are covered with millions of trees thanks to people living there more than a thousand years ago, a new study shows. Logging means the landscape is now one of the world’s most at-risk environments.
It had been thought the forests expanded due to wetter and warmer weather. But the research involving the University of Reading shows the rapidly expanding population of South America was really responsible.
"The so far believed to be ‘pristine’ forest is the result of co-existence and habitation between human and the forest for thousands of years" - Macarenas Cardenas, University of Reading
New excavations and soil analysis shows the forests, still hugely culturally and economically important to people living in South America, expanded between 1,410 and 900 years ago because of population growth and cultural changes.
Macarena Cardenas, a co-author from the Centre for Past Climate Change and Reading’s Department of Geography & Environmental Science, said: “Our research has demonstrated that the biodiversity that we know now for the iconic Araucaria forest of southern Brazil has been facilitated by indigenous human populations.
“The so far believed to be ‘pristine’ forest is the result of co-existence and habitation between human and the forest for thousands of years. The Araucaria forest would have supplied habitation and food facilities, and human would have lived within it, preserving and managing its diversity instead.”
The forests date back to the period when dinosaurs roamed, and are dominated by the iconic Araucaria or monkey puzzle trees, which have grown in the region for thousands of years and have been vital to communities living there. The trees are a valuable source of timber, fuel and resin, and the seeds are an abundant and reliable food source. They are now protected by strict laws, but logging has decimated the forests.
Of the 19 species of Araucaria tree, five are classified as endangered and two, including the Brazilian Araucaria angustifolia, are critically endangered. Reports from the late 1800s describe trees with diameters of over 2 m, reaching 42 m in height. Modern trees are only around 17.7 m tall.
The archaeological analysis began because the experts, from the University of Exeter, University of Reading, University of São Paulo, University of New Mexico, Universidade Federal de Pelotas and Universidade do Sul de Santa Caterina, noticed that in areas of low human activity forests are limited to south-facing slopes, whereas in areas of extensive archaeology, forests cover the entire landscape. They were able to analyse soil and archaeological evidence from Campo Belo do Sul, Santa Catarina State, Brazil, to test whether this pattern was directly related to past human activity.
The study shows the forests first expanded around 4,480 to 3,200 years ago, most likely near streams, and this may have been caused by a wetter climate. But a more rapid and extensive expansion across the whole region later happened between 1,410 and 900 years ago, when forests expanded into highland areas. The weather during this time was dry and less humid. This expansion of the forests coincides with population growth and increasingly complex and hierarchical societies in South America
The expansion in forests reached a peak around 800 years ago. The number of people in South America declined 400 years ago when European settlers arrived in the area. The population did not begin to recover until the 19 century, when loggers began exploiting the Araucaria forests for timber.
Dr Mark Robinson, from the University of Exeter, who led the British Academy-funded research, said: “These trees have been crucial to the culture, economy, society and diet of communities in the region, who used them for wood, resin, shade and food, and even based their idea of cosmology around the forests. Communities still call themselves ‘people of the Araucaria’, and hold festivals to celebrate the forests.
“This study shows the Araucaria forests were expanded beyond their natural boundaries, they were used sustainably for hundreds of years, and conservation strategies must reflect this so they balance protection, heritage and economic development.”
M. Robinson, J. Gregorio De Souza, S. Yoshi Maezumi, M. Cárdenas, L. Pessenda, K. Prufer, R. Corteletti, D. Scunderlick, F. Edward Mayle, P. De Blasis, J. Iriarte (2018). 'Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil'. Scientific Reports. Doi: 10.1038/s41598-018-24429-5