Regional vegetation changes in the tropical Andes expressed as arboreal pollen (AP%), standardised ordination scores (DCA z-scores), and aquatic vegetation ratios (D/SS); files used for plots

We compare eight pollen records reflecting climatic and environmental change from the tropical Andes. Our analysis focuses on the last 50 ka, with particular emphasis on the Pleistocene to Holocene transition. We explore ecological grouping and downcore ordination results as two approaches for extracting environmental variability from pollen records. We also use the records of aquatic and shoreline vegetation as markers for lake level fluctuations, and precipitation change. Our analysis focuses on the signature of millennial-scale variability in the tropical Andes, in particular, Heinrich stadials and Greenland interstadials. We identify rapid responses of the tropical vegetation to this climate variability, and relate differences between sites to moisture sources and site sensitivity.

Tropical climate and vegetation simulations during the Heinrich event 1 using an Earth System Model of Intermediate Complexity (EMIC) - the University of Victoria Earth System-Climate Model (UVic ESCM)

Abrupt climate changes from 18 to 15 thousand years before present (kyr BP) associated with Heinrich Event 1 (HE1) had a strong impact on vegetation patterns not only at high latitudes of the Northern Hemisphere, but also in the tropical regions around the Atlantic Ocean. To gain a better understanding of the linkage between high and low latitudes, we used the University of Victoria (UVic) Earth System-Climate Model (ESCM) with dynamical vegetation and land surface components to simulate four scenarios of climate-vegetation interaction: the pre-industrial era, the Last Glacial Maximum (LGM), and a Heinrich-like event with two different climate backgrounds (interglacial and glacial). We calculated mega-biomes from the plant-functional types (PFTs) generated by the model to allow for a direct comparison between model results and palynological vegetation reconstructions. Our calculated mega-biomes for the pre-industrial period and the LGM corresponded well with biome reconstructions of the modern and LGM time slices, respectively, except that our pre-industrial simulation predicted the dominance of grassland in southern Europe and our LGM simulation resulted in more forest cover in tropical and sub-tropical South America. The HE1-like simulation with a glacial climate background produced sea-surface temperature patterns and enhanced inter-hemispheric thermal gradients in accordance with the "bipolar seesaw" hypothesis. We found that the cooling of the Northern Hemisphere caused a southward shift of those PFTs that are indicative of an increased desertification and a retreat of broadleaf forests in West Africa and northern South America. The mega-biomes from our HE1 simulation agreed well with paleovegetation data from tropical Africa and northern South America. Thus, according to our model-data comparison, the reconstructed vegetation changes for the tropical regions around the Atlantic Ocean were physically consistent with the remote effects of a Heinrich event under a glacial climate background.

Pollen, DNA and Vegetation records from surface sediments of lacustrine lakes along a forest tundra - tundra transect at the Taymyr peninsula, northern Siberia

Reliable information of past vegetation changes are important to project future changes, especially for areas undergoing rapid transitioning such as the boreal treeline. The application of detailed sedDNA records has the potential to enhance our understanding of vegetation changes gained mainly from pollen studies of lake sediments. This study investigates sedDNA and pollen records from 31 lakes along a gradient of increasing larch forest cover in northern Siberia (Taymyr Peninsula) and compares them with vegetation field surveys within the lake's catchment. With respect to vegetation richness, sedDNA recorded 114 taxa, about half of them to species level, while pollen analyses identified 43 pollen taxa. Both approaches exceed the 31 taxa revealed by vegetation field surveys of 400 m**2 plots. From north to south, Larix percentages increase, as is consistently recorded by all three methods. Furthermore, tundra sites are separated from forested sites in the plots of the principal component analyses. Comparison of ordination results by Procrustes and Protest analyses yields a significant fit among all compared pairs of records. Despite the overall comparability of sedDNA and pollen analyses certain idiosyncrasies in the compositional signal are observed, such as high percentages of Alnus and Betula in all pollen spectra and high percentages of Salix in all sedDNA spectra. In conclusion, our results from the treeline show that sedDNA analyses perform better than pollen in recording site-specific richness (i.e. presence/absence of certain vegetation taxa in the direct vicinity of the lake) and perform as good as pollen in tracing regional vegetation composition.