Could paleoecology mark the age of humanity?

Nell Badgley

It is not uncommon to hear today’s times described as ecologically unprecedented.

Human-driven climate changes, species die-offs, and land use changes have starkly transformed our environment, so much that some scholars suggest this warrants the definition of a new geologic epoch– the Anthropocene, or “the age of humanity.” Yet are today’s changes truly unprecedented in the context of Earth’s history? 

Defining the Anthropocene on a continental scale 

Our current geologic epoch called the Holocene began approximately 11,700 years ago, as Earth transitioned out of its previous epoch known as the Pleistocene. This transition occurred over thousands of years and was marked not only by rapid warming, but also by a number of rapid ecological changes. A 2023 study by M. Allison Stegner and Trisha L. Spanbauer sought to illuminate whether the rapid vegetation changes that took place during the Pleistocene-Holocene transition are comparable to the rapid changes we are seeing today as a result of human influence. With this, we might better understand the question of whether today’s “unprecedented” changes might mimic the beginning of a new epoch like one Earth has experienced before.

In their paper “North American pollen records provide evidence for macroscale ecological changes in the Anthropocene”, Stegner and Spanbauer utilized sediment pollen records from the Neotoma Paleoecology Database to track changes in 7 elements over the past ~12,000 years: how taxonomic richness changed over time (SQS), dates of first and last appearances of species in the pollen record (FAD/LAD), short-term (1,000y) loss and gain of plants, and abrupt community changes (AC) to plant diversity.

 

 

Authors of the paper specifically elaborated on changes to FAD/LAD, as these changes are commonly used as markers for epoch transitions. As seen in Figure 1, FADs are elevated during the Pleistocene-Holocene transition around 11.7k YBP (years before present) and begin to increase in the past ~200 years, alongside LAD increases beginning ~1000 YBP. Furthermore, authors point to similar patterns in ACs and taxonomic richness (peaks around

Holocene-Pleistocene transition and in the last ~200 years) as further evidence of similarly abrupt changes occurring both during the last epoch transition and in recent centuries. 

What does this mean for Iowa?

Stegner and Spanbauer compared the past epoch transition to the rapid human-driven vegetation changes that have defined an era of human influence. But how does the

Anthropocene, a large-scale geologic epoch, translate locally? This paper began to break down regional changes based on 4 ecoregions but left out a significant swath of North America in these divisions. Notably, the Great Plains and Midwest are largely omitted from the paper’s dataset, meaning forested ecosystems are prioritized over the grassland and prairieland. As the pace of change defines Stegner and Spanbauer’s work, one may wonder whether the paleoecological history of the prairie-dominated ecosystems differed from the forest ecosystems highlighted in this research. 

We don’t have to be left completely in the dark as to Iowa’s paleoecological history, however, as a study by Baker et al. in 1996 took a different approach to understanding how the Holocene took shape in Northeast Iowa specifically. While Baker et al. relied on (fossil) pollen data in part, they also utilized plant macrofossils to reconstruct the specifics of past Holocene vegetation, mapping shifting forest, prairie, and human-disturbed ecosystems from around 12,000 years ago to today. Baker et al. attribute these changes to shifting climate, precipitation, temperature and fire regimes. But recent changes over the past few centuries certainly have shown evidence that humans have made their mark– disturbed ground and emerging cropland are key indicators that Iowa’s ecology had begun to shift as a result of humanity.

Despite this, what makes Stegner and Spanbauer’s work unique is their approach in highlighting species turnover (LAD/FAD). Whereas the work of Baker et al. has elucidated comprehensive species-composition level changes, Stegner and Spanbauer have highlighted markers crucial in understanding the epoch transitions–particularly the emergence of the Anthropocene. 

Unprecedented?

Ultimately, the abrupt vegetation changes that mark the potential Anthropocene are unprecedented because they are driven so markedly by human influence but are not so different in the context of what North America has seen over the last 12,000 years. The evidence is clear that humanity has made its mark on the continent’s vegetation, possibly also staking our place in geologic history.

Works cited 

Baker, R. G., Bettis III, E. A., Schwert, D. P., Horton, D. G., Chumbley, C. A., Gonzalez, L. A., & Reagan, M. K. (1996). Holocene paleoenvironments of northeast Iowa. Ecological Monographs, 66(2), 203-234.

Stegner, M. A., & Spanbauer, T. L. (2023). North American pollen records provide evidence for macroscale ecological changes in the Anthropocene. Proceedings of the National Academy of Sciences, 120(43), e2306815120.