Authors

Charlie A. Davies, J.S. Singarayer, O. J. Wilson, R. Cortele, J. Iriarte, and F.E. Mayle

University of Reading

Abstract

Brazil’s southern Atlantic Forest, a designated global biodiversity hotspot, is critically endangered, with less than 20% of its original forest cover remaining. Given its global importance and conservation priority, it is crucial to understand how to best maintain its ecosystem functioning and biodiversity in the face of increasing fire, drought, and deforestation, resulting from anthropogenic land use and climate change (Wilson et al., 2019, 2021). This study focuses on the highlands mosaic of Araucaria Forests and Campos Grasslands, the biomes most threatened, yet iconic and ancient formations. Throughout the Late Holocene, it’s evident that humans, climate, and fire all interacted and shaped the landscape (Wilson et al., 2022). However, the dynamic relationships between these interconnected factors remain unclear.

Palaeoecological studies have revealed that around 1000 years ago southern Brazil’s Araucaria Forests expanded, coinciding with expansion and increased cultural complexity of Indigenous southern Jê populations (Robinson et al., 2018). It is argued that the southern Jê enabled Araucaria expansion, due to the cultural importance of Araucaria angustifolia seeds (pinhão) as a critical food source to them. However, climate change has also been attributed as the main driver, as a shift to wetter and warmer conditions occurred at the time of Araucaria expansion in southern Brazil, with minor climatic shifts altering fire-forest feedback loops (Wilson et al., 2022). Discriminating between the effects of these potential drivers upon the Araucaria Forest remains difficult. The lines of evidence imply complex ways in which Indigenous peoples, climate change and fire interacted in southern Brazil during the Late Holocene. Therefore, complex combinations of factors, through space and time, must be considered to understand and effectively conserve Brazil’s vanishing Araucaria forests.

Using novel integrations of agent-based modelling (ABM), palaeo-data, and archaeology, we will assess how the southern Jê, climate change, and fire interacted and shaped these landscapes throughout the last 12,000 years. As these systems entail complex interdependencies, the ABM will allow us to see how the dynamics of their interactions unfold over time and space, something that cannot be done with just palaeo-data and archaeology. In this model, southern Jê populations will act as “agents” interacting with their environments and each other. Their behavioural rules will be based on archaeological and ethnographical records from southern Brazil and will include, for example, their uses of Araucaria and production of agricultural resources such as maize. The environment, where the agents interact, will represent the Araucaria Forest biome through the integration of existing topographic, vegetation, and ecological niche modelling. Climate data will also be integrated into the model, using climate models and existing palaeoclimate data from the region. The model formulation will allow representation of fire in the model, through both natural and human drivers. The model simulations will be validated using the palaeoecological and archaeological records from the region, to test if results of Araucaria expansion and southern Jê populations represent what happened historically during the Holocene.

Integration of both human and climate factors in the ABM will allow us to run different scenarios to establish their roles in the expansion of Araucaria Forests. We hypothesize that human influence alone will not cause modelled expansion of the forests. For Araucaria Forests to expand, we expect that in periods of we\er, warmer climates, minor shifts altering fire-forest feedback loops will assist in forest expansion by reducing fire (Wilson et al., 2022). In areas of low-density southern Jê occupations, we expect forest to expand further. However, in high-density southern Jê occupations, forest expansion but to a lesser extent is expected, due to transformations of the landscape by the southern Jê, through crop cultivation and setting more fires.

Our results should address the uncertainties and complexities regarding drivers of Araucaria Forest expansion in southern Brazil. Through understanding the interactions between Indigenous people, climate, and fire in the Araucaria Forests during the Holocene, we should be able to be\er understand the ecosystems’ resilience to current and future anthropogenic and climate changes.

References:

Wilson, O. J., Walters, R. J., Mayle, F. E., Lingner, D. v., & Vibrans, A. C. (2019). Cold spot microrefugia hold the key to survival for Brazil’s Critically Endangered Araucaria tree. Global Change Biology, 25(12), 4339–4351. https://doi.org/10.1111/gcb.14755

Wilson, O. J., Mayle, F. E., Walters, R. J., Lingner, D. v., & Vibrans, A. C. (2021). Floristic change in Brazil’s Southern Atlantic Forest biodiversity hotspot: From the last glacial maximum to the late 21st century. Quaternary Science Reviews, 264. https://doi.org/10.1016/j.quascirev.2021.107005

Wilson, O. J., (2022). Assessing the resilience of Brazil’s iconic Araucaria Forests to past and future climate change. Unpublished PhD thesis. University of Reading.

Robinson, M., de Souza, J. G., Maezumi, S. Y., Cárdenas, M., Pessenda, L., Prufer, K., Cortele7, R., Scunderlick, D., Mayle, F. E., de Blasis, P., & Iriarte, J. (2018). Uncoupling human and climate drivers of late Holocene vegetation change in southern Brazil. Scientific Reports, 8(1), 7800. https://doi.org/10.1038/s41598-018-24429-5