Global acceleration in rates of vegetation change is unprecedented over the last 18,000 years
The acceleration of biodiversity change began millennia ago and was often larger than the shift from the last ice age to modern temperatures, a UiB study published in Science shows.
In the paper, the authors assess global patterns of rates of vegetation change from the last deglaciation, through the Holocene, and up to the recent years, covering all continents except Antarctica. Rate of change is the magnitude of change over a defined period of time, and it can be used to describe if an ecosystem is changing faster or slower. This assessment provides crucial insights into the degree of change that vegetation endured over the last 18.000 yr on a global scale.
From lakes to rates of vegetation change. Fossil pollen records offer our best insights into past rates of vegetation change. A lake, or other suitable environment, is cored to retrieve the layered sediments which usually contain pollen grains that accumulated over thousands of years. By identifying and counting the different pollen grains researchers can then reconstruct the local vegetation composition. Finally, the rate of vegetation change is estimated from the changes in pollen abundances through time.
"Vegetation always changes to some degree through time. It changes because of climate or humans, or due to both. By looking into responses of vegetation during the last 18.000 years, we see that the degree of vegetation change has not been synchronous in space, meaning that vegetation changed at different moments and magnitudes. During substantial climatic changes, such as when the world warmed after the last ice age 18 thousand years ago, some areas responded similarly, like across temperate zones. However, we see this pattern wasn’t necessarily echoed in the tropics, so there was no such thing as one global vegetation response to climate," says Dr. Suzette Flantua.
Lead author's profile - Dr Flantua. Dr. Suzette Flantua is a global change ecologist at the University of Bergen (UiB) and the Bjerknes Centre for Climate Research in Norway. Together with Dr. Ondřej Mottl, UiB data scientist, they are the first authors of the recent paper published in Science on global rates of vegetation change over the last 18,000 years.
Pollen is key
Dr. Flantua is a global change ecologist at the University of Bergen (UiB) and the Bjerknes Centre for Climate Research in Norway. Together with Dr. Ondřej Mottl, UiB data scientist, they are the first authors of a paper published in Science (Mottl, Flantua et al 2021).
Their outcomes are based on 1181 fossil pollen records derived from the open-access Neotoma Paleoecology Database, a global data resource that stores multiple kinds of fossil, palaeoecological, and paleoenvironmental data.
Analysing such large quantities of data is no small feat. Mottl explains that estimating rates of vegetation change based on existing metrics had been seen as unreliable in the palaeoecological community due to various issues. However, together with UiB and international colleagues, they came up with a new approach which has been presented in related paper and recent R package, called R-Ratepol.
"The process of developing a new rate of change method resulted from a workshop with a lot of scientific discussions with other members of our team. Then I basically got my head down and figured out a way to apply the theory into the code. For me that is the best part, to find an issue, put it into code, and then solve it" Mottl laughs.
Change on a global scale
The paper shows that approximately 4000 years ago, rates of vegetation change started to accelerate up until the present and such patterns are unambiguously global.
"It gave us a good understanding of the impact of our paper. Since most ecologists, studying current ecosystems, have records dating back decades or in some cases 100 years, so they are inclined to think that more drastic changes in vegetation started more recently. We show that the legacy of an accelerated change goes even further back. It has major implications for how we perceive our natural world right now," Mottl explains.
Fossil pollen track global patterns
“One of my main research interests is to find ways to harness the information from long-term ecological datasets to better understand present-day patterns of biodiversity”, said Alistair Seddon, a global change ecologist and part of the senior authorship team. “This paper does just that and provides an example of how fossil pollen can be used to track global patterns of biodiversity over much longer timescales. It also opens up the door to a number of other exciting research questions”.
For example, the plan forward is to integrate information on climate and archaeological data of human populations, and further look into the relationship with vegetation change. That is one of the goals of the Human on Planet Earth (HOPE) project, led by Emeritus Prof. John Birks, UiB paleoecologist. “It is very important to understand what caused these changes. We provided context in our paper, but we stressed that more work is needed to exactly pinpoint what caused such accelerations." Flantua explains. "If we know more about the past, we can assess the present in a better way, and hopefully impact the future," Mottl adds.