For more than 11,000 years, the Linje peatland in northern Poland has quietly recorded how climate and ecosystems have changed over time.  

By studying layers of preserved mosses and plants trapped in the peat, researcher Eliise Poolma contributed to an international effort to reconstruct one of the most complete environmental histories of the Holocene ever found in Central Europe. Their work demonstrates how this peatland responded to warmer and cooler periods, sudden climate shifts, and, more recently, human activity. Long‑term insights from this multi-proxy study reveal how landscapes reacted to past changes and why that history matters today as we face rapid climate change. 

Eliise joins the P2F project as a PhD student at Tallinn University of Technology in Estonia, where she studies postglacial climate change in Northern and Central Europe. Here, she shares insights from her recent publication in EGU Climate of the Past and her upcoming work. 

How would you describe your research journey?

I would be happy to call myself a palaeobotanist, as my work combines modern plant knowledge with the study of subfossil material.  

My interest in palaeobotany developed gradually through my academic path. It started with specialising in botany during my biology studies and grew stronger during my master’s degree, when I worked on endangered aquatic plants. During that project, we began looking at lake sediment seed banks, which became a real turning point for me. My first experiences identifying plants from seeds opened up a completely new and fascinating world. I am always happy to be outdoors, collecting plant material to build a reference collection and learning about plant ecology, and I also enjoy the process of microscopic identification, which I continue to find both challenging and exciting.

The multi‑proxy approach combining testate amoebae and plant macrofossils was central to your reconstruction. How do these proxies complement each other, and what kinds of climate and ecological signals do they allow you to detect?

In peatlands, testate amoebae and plant macrofossils are ecologically linked, which makes them highly complementary proxies. In Linje mire we used both to reconstruct past hydrological and trophic changes. 

Peatland plants, on the other hand, respond more slowly. For example, Sphagnum moss species can tolerate periods of lower water tables and recover when conditions improve, so their signal in the fossil record reflects longer-term ecological trends. They can also be used for quantitative reconstructions, but in Linje we used plant macrofossil data for a semi-quantitative approach. 

Using both proxies together allows us to identify synchronous changes across different response times, increasing confidence in our interpretation of hydrological and ecological change. 

The study suggests evidence of human impact on the peatland environment in the Late Holocene. What factors determine changes are driven by human activity?

It depends largely on the archaeological and palaeoecological context. When archaeological evidence, pollen data, and charcoal records indicate sustained human presence in the vicinity of a peatland, separating human-induced signals from climate-driven changes becomes difficult, and in some cases impossible. 

In the case of Linje, earlier studies show that humans were already affecting the surrounding landscape around 3000 years ago. As a result, we could no longer claim with full confidence that the changes were entirely climate-driven. Human impact does not necessarily involve direct disturbance of the peatland itself; for example, large-scale deforestation in the surrounding catchment can alter peatland hydrology. 

At Linje peatland, there is also clear historical and visual evidence of direct human impact, such as drainage and peat cutting. These activities disturbed the upper peat layers, making them unsuitable for reliable climate reconstruction. Consequently, the noticeable Late Holocene changes in the topmost part of the profile are best interpreted as reflecting human influence rather than regional climate signals. 

Past to Future, like most paleoclimate research, relies on a lineage of prior research, from method development to sample collection. What is it like to contribute to this growing body of work, and what questions are you excited to explore next?

I am very grateful that the Polish paleoecology team trusted me with such unique material and allowed me to contribute another piece of knowledge about the Linje peatland. Complete, well-preserved records like this are rare, and I am well aware that research at Linje did not start with me and will continue well beyond my contribution. 

Back in 2019, when the samples were collected, I had no idea that one day I would be a junior researcher working with peatlands. Nevertheless, in 2022, I began collaborating closely with an international team on the Linje peat profile. I wonder how these records will be revisited and reinterpreted in the future as methods and research questions continue to evolve. 

Within the Past to Future project, I am happy to continue contributing palaeoclimate data from Linje and elsewhere. I am currently excited about exploring changes in the past growing season using subfossil leaf material from Linje peatland. This work has the potential to provide a unique long-term dataset on past growing-season conditions, which are highly relevant today for both ecosystem functioning and the economy. I see this as a valuable contribution also to broader discussions about how vegetation seasonality may respond to future climate change and impact us all. 

Follow Eliise’s research.

Read the full study. 

Poolma, E., Marcisz, K., Amon, L., Fiutek, P., Kołaczek, P., Leszczyńska, K., Mauquoy, D., Słowiński, M., Veski, S., Wagner-Cremer, F., and Lamentowicz, M.: The most complete Holocene peat record from Central Europe: multi-proxy reconstruction of postglacial wetness changes and climate events from Linje peatland, Poland, Clim. Past, 21, 1933–1959, https://doi.org/10.5194/cp-21-1933-2025, 2025.