Long-term fire and vegetation change in northwestern Amazonia

Quantifying past forest cover and biomass changes in the Ecuadorian Amazon

Here, we developed and applied models to quantitatively reconstruct forest cover and biomass changes at three lakes in northwestern Amazonia over the past > 1500 yr. We used remotely sensed data and a modern dataset of 50 Amazonian lakes to develop generalized linear models that predict aboveground biomass, using phytolith morphotypes and forest cover as predictor variables. Also, we applied a published beta regression model to predict forest cover within 200 m of each lake, using Poaceae phytoliths. Charcoal and maize phytoliths were analysed to identify past land use. Results showed forest cover and biomass changes at our study sites ranged between 48-84% and 142-438 Mg ha-1, respectively. Human occupation was discontinuous, with major changes in forest cover and biomass coinciding with periods of land use. Forest cover and biomass decreased notably after fire (at all sites) or cultivation events (Lakes Zancudococha, Kumpaka). The timing and ecological impact of past land use were spatially and temporally variable. Our results suggest past human impact was small-scaled and heterogenous in northwestern Amazonia, with a significant impact of fire on forest cover and biomass changes.

Past Fire and Vegetation Change in the Hyperdiverse Forests of the Ecuadorian Amazon

The Ecuadorian Amazon holds more biodiversity than most other places on Earth. Palms are a particularly dominant component of the vegetation; however, it remains unknown to what degree the pattern has persisted through time. Here, we investigate the persistence of palm dominance through time and the degree to which past human activities (e.g., fire, cultivation, and forest opening) have affected changes in palm abundances across five regions of the Ecuadorian Amazon. We analyzed soil cores (40-80 cm depth) from each region for charcoal (evidence of past fire) and phytoliths (evidence of past vegetation change). The timings of fires (based on 14C radiocarbon dates), the occurrence, recurrence, and number of fires (based on charcoal presence and abundance in samples), and the amount of change in palm abundances (based on phytoliths) varied within and between the studied regions. The charcoal and phytolith results indicate the presence of low levels of past human activity at all sites. Our results show that patterns of modern palm hyperdominance found in Amazonian forests have not been persistent through time, and that even low levels of past human activities can affect palm abundance.

Pre-contact and post-colonial ecological legacies shape Surinamese rainforests

Disturbances in tropical forests can have long-lasting ecological impacts, but their manifestations (ecological legacies) in modern forests are uncertain. Many Amazonian forests bear the mark of past soil modifications, species enrichments, and fire events, but the trajectories of ecological legacies from the pre-contact or post-colonial period remain relatively unexplored. We assessed the fire and vegetation history from 15 soil cores ranging from 0 to 10 km from a post-colonial Surinamese archaeological site. We show that (1) fires occurred from 96 bc to recent times and induced significant vegetation change, (2) persistent ecological legacies from pre-contact and post-colonial fire and deforestation practices were mainly within 1 km of the archaeological site, and (3) palm enrichment of Attalea, Oenocarpus and Astrocaryum occurred within 0, 1, and 8 km of the archaeological site, respectively. Our results challenge the notion of spatially extensive and persistent ecological legacies. Instead, our data indicate that the persistence and extent of ecological legacies are dependent on their timing, frequency, type, and intensity. Examining the mechanisms and manifestations of ecological legacies is crucial in assessing forest resilience and Indigenous and local land rights in the highly threatened Amazonian forests.