Locally extensive pre-Columbian human occupation and modification occurred in the forests of the central and eastern Amazon Basin, but whether comparable impacts extend westward and into the vast terra firme (interfluvial) zones, remains unclear. We analyzed soils from 55 sites across central and western Amazonia to assess the history of human occupation. Sparse occurrences of charcoal and the lack of phytoliths from agricultural and disturbance species in the soils during pre-Columbian times indicated that human impacts on interfluvial forests were small, infrequent, and highly localized. No human artifacts or modified soils were found at any site surveyed. Riverine bluff areas also appeared less heavily occupied and disturbed than similar settings elsewhere. Our data indicate that human impacts on Amazonian forests were heterogeneous across this vast landscape.

Aim To determine if recurrent fire accounts for bamboo-dominated forests that cover about 180,000 km 2 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 (BÀ) 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 BÀ 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 BÀ 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 BÀ 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.

1. Modifications of Amazonian forests by pre-Columbian peoples are thought to have left ecological legacies that have persisted to the modern day. Most Amazonian palaeoecological records do not, however, provide the required temporal resolution to document the nuanced changes of pre-Columbian disturbance or postdisturbance succession and recovery, making it difficult to detect any direct, or indirect, ecological legacies on tree species. 2. Here, we investigate the fossil pollen, phytolith and charcoal history of Lake Kumpak a , Ecuador, during the last 2,415 years in c. 3-50 year time intervals to assess ecological legacies resulting from pre-Columbian forest modification, disturbance, cultivation and fire usage. 3. Two cycles of pre-Columbian cultivation (one including slash-and-burn cultivation, the other including slash-and-mulch cultivation) were documented in the record around 2150-1430 cal. year BP and 1250-680 cal. year BP, with following postdisturbance succession dynamics. Modern disturbance was documented after c. 10 cal. year BP. The modern disturbance produced a plant composition unlike those of the two past disturbances, as fire frequencies reached their peak in the 2,415-year record. The disturbance periods varied in intensity and duration, while the overturn of taxa following a disturbance lasted for hundreds of years. The recovery periods following pre-Columbian disturbance shared some similar patterns of early succession, but the longer-term recovery patterns differed. 4. Synthesis. The trajectories of change after a cessation of cultivation can be anticipated to differ depending on the intensity, scale, duration and manner of the past disturbance. In the Kumpak a record, no evidence of persistent enrichment or depletion of intentionally altered taxa (i.e. direct legacy effects) was found but indirect legacy effects, however, were documented and have persisted to the modern day. These findings highlight the strengths of using empirical data to reconstruct past change rather than relying solely on modern plant populations to infer past human management and ecological legacies, and challenge some of the current hypotheses involving the persistence of pre-Columbian legacies on modern plant populations. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

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