Plant Freezing Would Have Limited the Distribution of Forests 300 Million Years Ago

Why do forests exist as they do today? Why are they made up of certain species of trees and distributed across Earth as they are? What environmental factors contributed to these evolutionary patterns? New research published in Proceedings of the National Academy of Sciences of the United States of America (PNAS) by a team of scientists that includes Haverford Associate Professor of Environmental Studies Jonathan Wilson seeks to answer some of these questions by focusing on the role of low temperatures in shaping terrestrial forests. 

“With this study, we are demonstrating that some of the patterns and processes that we recognize from recent geologic history, such as glacial ice limiting the distribution of trees during the Last Glacial Maximum more than 21,000 years ago, were operating in the deep geological past, more than 300 million years ago, during a period called the Late Paleozoic Ice Age,” says Wilson. “During this time, plants were subjected to climatic extremes of frost and drought, and the plant lineages that could adapt to these extremes went on to shape landscapes to this day.”

This research, which used computational models combined with mathematical parameters of plant functions derived from analysis of living plants and fossilized plant material, is important because learning more about plant growth—or what inhibits it—and vegetation patterns hundreds of millions of years ago can help scientists better understand evolutionary history, and, according to Wilson, “shows us that the distant past looks more familiar than we previously thought.”

“Our study helps us think about forests in two ways,” he says. “First, it helps us appreciate that cold temperatures can be an important evolutionary constraint, alongside more familiar threats, such as drought and fire—and that this has been true for hundreds of millions of years, and not only the recent past. Second, this study helps us consider the ways that limits to plant growth affect other parts of the Earth system. In the case of the Late Paleozoic forests, the absence of plants because it was too cold likely had significant effects on runoff and nutrient flow to the oceans, which, in turn, had consequences for the climate as a whole.”

Wilson’s Haverford lab investigates the coevolution of plants and the environment over the last 475 million years as a way to understand climate change, the evolutionary trajectory of plant adaptations, and ecosystem responses to mass extinctions. He has been collaborating with researchers from Baylor University; University of Michigan; University of California, Davis; Trinity College, Dublin; the Smithsonian Institute; and the University of Connecticut for years on this project. He contributed work in the fossil plant process, searching for answers to fundamental questions about how the extinct plants functioned. Several of his students, including Remmy Chen '16, Brian Keller '18, Charlie Marquardt '16, Greg Miraglia '14, Gabe Oppler '17, Deana Rauh '16, Liz Reikowski '17, and Jessie Smart '18 participated in this research. 

“Our team used a series of analyses to make our simulations as close to reality as possible, including making measurements of features in fossil plant leaves and stems, and conducting experiments on living plants in growth chambers,” says Wilson.

The research team hopes that this work inspires others to undertake additional plant-evolution modeling efforts of other eras of environmental history—especially since a better, more detailed timeline would help us not only better understand the past, but also, perhaps, the future. 

“As we consider the range of impacts from anthropogenic climate change,” says Wilson, “what happened during the Paleozoic Era is a cautionary tale: changes to terrestrial systems affected far more of the planet than only the forests themselves.”
 

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