Historical fire and bamboo dynamics in western Amazonia

Aim To determine if recurrent fire accounts for bamboo-dominated forests that cover about 180,000 km2 of western Amazonia. Location Western Amazonia, including Los Amigos and Cocha Cashu, Peru, and Acre, Brazil. Methods We identified bamboo (B+) and closed-canopy forests (B-) using a combination of MODIS imagery, Landsat TM imagery and field surveys. Local-scale and landscape-scale patterns of historical bamboo dynamics were analysed by collecting soil cores from B+ and B- sites across three regions. Soil charcoal within cores was used to document previous fire, and phytoliths were employed to reconstruct vegetational patterns through time. Results Fire occurred in B+ and B- sites with approximately equal frequencies in each region sampled. Between regions, fire signals were most prevalent at Los Amigos, with Cocha Cashu and Acre sites typically containing only trace amounts of charcoal. Vegetational state remained constant through time in both B+ and B- forests of Cocha Cashu and Acre. The persistence of bamboo through time is less clear at Los Amigos, with bamboo presence changing both spatially and temporally. Main conclusions Fire does not appear to be the driving mechanism behind current bamboo distributions, although it may facilitate bamboo invasion. Once established in an area, bamboo persistently dominates the vegetation structure over historical time-scales at some sites (Cocha Cashu and Acre), but not at others (Los Amigos), which is likely to be a function of patch origin. Increasing human activity, including fire and deforestation, combined with predicted Amazonian drought, may allow bamboo to expand from its current distribution and replace typical Amazonian closed-canopy forests. These structural changes in the forests have important implications for carbon storage, as Amazonian forests are currently the largest terrestrial carbon sink in the world.