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Changes in Earth's vegetation are the fastest in 18,000 years

A new study based on the analysis of ancient pollen samples has revealed that Earth’s vegetation is changing faster today than it has over the last 18,000 years. An international team of researchers used a new statistical approach to investigate how much humans and climate change have altered landscapes worldwide. 

Study co-author Sarah Ivory is an assistant professor of Geosciences in the College of Earth and Mineral Sciences at Penn State.

“We know that climate and people interact with natural ecosystems and change them,” said Professor Ivory. “Typically, we go to some particular location and study this by teasing apart these influences. In particular, we know that the impact people have goes back much earlier than what is typically accepted as the case. However, we haven’t been able to observe the patterns created by these processes globally or long-term.”

The experts analyzed more than 1,100 fossil pollen records from Neotoma Paleoecology Database. The goal of the analysis was to examine how plant ecosystems have changed since the end of the last ice age about 18,000 years ago, and how quickly the changes have occurred.

“At the end of the ice age, we had complete, biome-scale ecosystem conversions,” said Professor Jack Williams of the University of Wisconsin-Madison. “And over the past few thousand years, we’re at that scale again. It has changed that much. And these changes began earlier than we might have thought before.”

Beyond the major changes in vegetation associated with the end of the last ice age, the team identified another major signal of change that corresponded with the expansion of agriculture, which occurred 3,000 to 4,000 years ago.

“We detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent,” wrote the study authors. “The scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformation of the last deglaciation.”

Professor Ivory noted that humans were influencing vegetation long before agriculture became a major factor.

“People have a presence, they are everywhere. Even in places that are not very urbanized or might appear to be quite wild, often in the archaeological and fossil pollen record, we see legacies of the impact of people very early,” said Professor Ivory. 

“How do biodiversity and resources change through time with respect to climate change and the impact that people have already had? How is it likely to change in the future?” 

“There were a lot of dynamic things happening over the last 11,000 years. Ecosystems were reorganizing. Many of the megafauna went away. It’s hard to explain all that without climate. However, during the later part of this period, there aren’t major climate changes, so it is more likely human technology that is responsible.”

According to the researchers, the current rate of change among Earth’s plant communities rivals or exceeds the rapid turnover that took place as plants raced to adapt to a global climate that warmed by about 10 degrees Fahrenheit. The research suggests ecosystem rates of change will continue to speed up over the coming decades.

The current geological age, during which human activity has been the dominant influence on the environment, is referred to as the Anthropocene.

“And one of the questions has been, when did the Anthropocene begin?” said Professor Williams. “This work suggests that 3,000 to 4,000 years ago, humans were already having an enormous impact on the world that continues today.”

The study is published in the journal Science.

By Chrissy Sexton, Staff Writer

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