Dr. Joy Ward at the University of Kansas is looking at how rising levels of carbon dioxide in the atmosphere may be impacting trees around the world and even causing them to adapt. By looking at ancient tree specimens from the Ice Age, Ward is able to see how trees in the past have adapted, helping her understand how trees may adapt today and in the future. Changing Planet is produced in partnership with the National Science Foundation.
Survival of Trees
ANNE THOMPSON, reporting:
Tall, majestic and inspiring, trees are the skyscrapers of nature. They're also an essential part of the planet's ecological health, providing oxygen to the air, limiting erosion in the soil, and offering countless other benefits to birds, animals and people.
But rising temperatures and drier conditions due to climate change are wreaking havoc on the world's forests, including the United States. A 2009 study published in the Journal "Science" finds that trees are dying twice as fast as they did just 30 years ago in the older forests of the western United States. Evidence of how trees respond to changing conditions isn't found just by surveying forests, but also by studying the annual rings formed within each individual tree.
Dr. JOY WARD (Plant Ecologist, University of Kansas): We may measure tree rings, the width of those tree rings on an individual tree. And from there we can get a sense of how much the climate varies over the life cycle of that tree.
THOMPSON: Dr. Joy Ward is a plant ecologist at the University of Kansas and funded by the National Science Foundation. With the help of her students, she's looking at how trees have responded, and adapted, to changes in carbon dioxide found in the atmosphere. These records go back tens of thousands of years, all the way to the Ice Age.
WARD: The Ice Age provides us an interesting snapshot of a period where carbon dioxide was the lowest during the evolution of land plants.
THOMPSON: The last Ice Age, which ended over ten thousand years ago, covered much of the northern hemisphere with ice. It was a time when creatures like saber-tooth tigers and giant woolly mammoths roamed the earth. Plants and trees were also different because carbon dioxide, their main food source, was at much lower levels. As carbon dioxide levels change, plants have to quickly adapt or go extinct.
WARD: Change in carbon dioxide is one of those factors that plants may have variable response to very rapidly, and we have evidence for that in our laboratory.
THOMPSON: For her research, Ward uses samples from Ice Age-era trees that have been perfectly preserved for tens of thousands of years, such as this juniper tree specimen from the La Brea tar pits in Los Angeles, or this kauri tree specimen from muddy bogs in New Zealand.
WARD: The peak of the last glacial period was twenty thousand years ago, but these trees would be well within the glacial time period. This particular tree would have been growing during the last glacial period when temperatures were much cooler and carbon dioxide was much lower than today.
THOMPSON: Drilling tiny holes into the tree's rings, Ward carefully gathers samples to analyze in the lab.
WARD: This is only wood sawdust from one particular year of this tree's life and then we can analyze this to understand how it was functioning during that time period as well as measure the width of that ring to know how much it grew that year.
THOMPSON: What Ward and her team find most valuable about their data is that they can compare it to tree and plant specimens living today.
WARD: What we can do at some level is look at growth patterns in these forty thousand year old trees and compare them with modern trees and potentially get some insight into how carbon dioxide may have influenced growth.
THOMPSON: Looking at the tree specimens at the genetic level, Ward says trees have adapted to changes in carbon dioxide levels over many generations.
WARD: But even in several tens of thousands of years, to thousands of years, we believe there is potential for genetic change and evolution in response to environmental conditions. So we look at key genes that might be selected on for evolution as plants continually respond to this over multiple generations, not just one generation.
THOMPSON: By studying how tree genes have adapted to carbon dioxide in the past, Ward hopes to understand which tree species will be able to survive, and evolve, in the rapidly changing conditions of today and in the future.
WARD: That's what we're concerned about here is that with rising carbon dioxide, because carbon dioxide is essentially a plant's food source, we suspect and have strong evidence that that can induce very rapid changes in the kinds of genotypes that are most successful. And that would change gene frequencies into the future. And that's in a nutshell the type of evolution that we're talking about here.
THOMPSON: In her lab, Ward is even creating controlled climate conditions, where the carbon dioxide and temperature levels are set for predicted future levels, to see how plants will react.
WARD: And so this gives us insights into how a plant functioned under limiting carbon dioxide conditions, which helps us understand how it might respond as carbon dioxide levels continue to rise into the future and so we have a larger timeline of understanding by including these ancient trees in this kind of climate change work.
THOMPSON: Whether studying the past, analyzing the present, or testing for the future, Ward hopes to unlock the secrets of plant survival sealed within the rings of these majestic trees.
The baobab tree, sometimes called the "Tree of Life," has an unforgettable appearance. Found in savanna regions of Africa, Madagascar and Australia, the trees form a very thick and wide trunk and mainly branch high above the ground. They can grow to be thousands of years old, and develop hollows inside so large that one massive baobab in South Africa had a bar inside it.
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