Bamboo-dominated forests and pre-Columbian earthwork formations in south-western Amazonia

Aim To determine whether the c. 160,000 km 2 patch of bamboo-dominated forests (Guadua spp.) in Amazonia is associated with pre-Columbian earthwork (geoglyph) formation. Location South-western Amazonia. Methods We modelled the distribution of Guadua-dominated forests and geoglyphs with Maxent, which uses occurrence points and a suite of environmental parameters. We compared the modelled distribution of Guadua with mapped distributions derived from remote sensing data, and with the modelled distribution of geoglyphs. Results The modelled Guadua distribution closely fitted previously mapped estimates. Based on our analyses, the best predictors for the distribution of Guadua-dominated forests are temperature seasonality and close proximity to hilly terrain. Distance to bamboo forest and precipitation of the driest quarter were the most significant predictors of geoglyph distributions. Main conclusions This study suggests that the most parsimonious explanation for the association of geoglyphs and bamboo forests in south-western Amazonia is that pre-Columbian people constructed geoglyphs near the edges of the semelparous Guadua forests. After die-off events, the large fuel load of dead vegetation would burn easily, providing a much easier mechanism of forest clearing than was possible in closed-canopy forests. These results highlight the interplay of ancient human activity with observed biogeographical patterns, and suggest that pre-Columbian settlement patterns may reflect the heterogeneity of forest types found within Amazonian rain forests.