Aim: We aim to assess i) how pollen assemblages vary across biogeographic and environmental gradients, ii) the source area of pollen assemblages from lake sediment samples, and iii) which pollen taxa can best be used to quantify deforested landscapes.

Location: Amazonia

Taxon: Plantae

Methods: Pollen assemblages (N = 65) from mud-water interface samples (representing modern conditions) of lake sediment cores were analysed and compared with modern gradients of temperature, precipitation, and elevation. Pollen assemblages were also compared with local scale estimates of forest cover at 1, 2, 5, 10, 20, and 40 km buffers around each lake.

Results: Over 250 pollen types were identified in the samples, and pollen assemblages were able to accurately differentiate biographic regions across the basin, corresponding with gradients in temperature and precipitation. Poaceae percentages had a significant negative relationship with forest cover estimates, which were stronger at the 1 km buffer and weaker as buffer sizes increased.

Main conclusions: The diverse Amazonian pollen assemblages strongly reflect environmental gradients, and percentages of Poaceae best reflect local scale variability in forest cover. Our results of modern pollen-landscape relationships can be used to provide a foundation for quantitative reconstructions of climate and deforestation in Amazonian landscapes.

A total of 65 sites located within Amazonia sensu stricto (Eva et al., 2005) were used in our analysis (Fig. 1, Table S1). Samples from new sites (n = 44) were collected with a Universal corer during 2018 and 2019 (Table S1). Samples from previously published sites (n = 21) were collected with a Colinvaux-Vohnout piston corer or a Universal corer (Table S1) (Bush et al., 2020). Our sites were located within evergreen tropical rainforests (n = 56) and from savannas close to the ecotone with forests (n = 9) (Fig 1a). Thirty-three of the forested sites were situated within terra firme soils and 22 on floodplains (Table S1). The sites included permanent lakes, oxbow lakes, and flooded marshes in the Brazilian savannas (Table S1).

From each of the 65 sites, we collected the upper 1 cm of sediment (mud-water interface) for pollen analysis. Pollen samples were prepared in the Paleoecological Laboratory at the Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Netherlands or in the Neotropical Paleoecology Laboratory at Florida Institute of Technology, USA, and followed standard procedures as documented in Faegri and Iversen (1989). A total number of 300 to 500 pollen grains were counted to generate a pollen assemblage for each sample, and tablets of Lycopodium clavatum spores were added prior to sample preparation to allow for calculations of pollen concentration (Stockmar, 1971). Pollen identification of the new samples was at a lower taxonomic resolution than the previously published samples, and data were harmonized (e.g., merged to a higher taxonomic resolution) prior to analysis (e.g., Bush et al., 2020).