Accelerated rates of change in Earth’s vegetation go back thousands of years

Climate changes and human activities have transformed our planet’s ecosystems over the last 18 000 years. While scientists know a lot about the environmental changes that have happened since the Industrial Revolution in the mid-18th century, they lack comprehensive knowledge about how much and how fast global vegetation changed in the preceding millennia.

A new study supported by the EU-funded HOPE project has now discovered that the rates of change in the planet’s vegetation began to speed up many thousands of years ago. “What we see today is just the tip of the iceberg,” comments co-lead author Dr Ondřej Mottl from HOPE project host University of Bergen, Norway, in a news release posted on ‘EurekAlert!’. “The accelerations we see during the industrial revolution and modern periods have a deep-rooted history stretching back in time.”The international research team used a global set of 1 181 fossil pollen records to which they applied new statistical methods to determine how and how fast the world’s plant communities have changed in the past 18 000 years. Fossil pollen is a valuable tool for reconstructing the history of changes in vegetation and consequently the climate. When pollen from plants is washed or blown into ponds, lakes or oceans, it settles in sediment layers at the bottom of these bodies of water. Scientists take core samples of these layers to find out what kinds of plants were growing at the time the sediment was deposited. With this knowledge, they can also determine human impact on ecosystems.

Using these pollen records, the researchers identified a first peak in the rate of change of plant communities around 11 000 years ago, when the planet was coming out of the last ice age. “We expected rates of ecological change to be globally high during this transition because the world was changing fast as glaciers retreated and the world warmed,” observes co-lead author Suzette Flantua, also from the University of Bergen.

The planet’s ecosystems then stabilised, until somewhere between 4.6 and 2.9 thousand years ago when a second period of accelerating change began that continues to this day. These changes to the world’s plant ecosystems are now at least as fast as the great transformations that occurred at the end of the last ice age. “That was a surprising finding, because over the last few thousand years, not a whole lot was happening climatically, but the rates of ecosystem change were as big or bigger than anything we’ve seen from the last ice age to the present,” remarks co-author Prof. John Williams of the University of Wisconsin-Madison, United States of America, in an article posted on ‘ScienceDaily’. Interestingly, this accelerated change began for terrestrial communities as a whole, which according to the authors, as the study notes, suggests that the past two centuries’ “acceleration in turnover … is the tip of a deeper trend.”

Speaking about the vegetation changes in the ‘EurekAlert!’ news item, Dr Mottl states: “Although some patterns seem more obvious than others, we are actually not sure which changes were caused by humans, climate, or both.” Next on the agenda for research work supported by the HOPE (Humans On Planet Earth - Long-term impacts on biosphere dynamics) project is to gain more insight into the interaction between climate, humans and ecosystems by comparing the global fossil data with independent climate change and archaeological data.

For more information, please see:

HOPE project web page