Airborne mapping sheds light on climate sensitivity of California redwoods
June 24, 2020
Throughout California, the effects of climate change are evident, from increasing frequencies of intense wildfires and mudslides to widespread and prolonged droughts. These changes also threaten one of California’s most iconic endemic species: coastal redwoods. Coastal redwoods are not only some of the tallest and oldest trees on Earth, but redwood forests are also capable of storing three times more carbon than any other forest. Identifying suitable habitats for these vulnerable species has important implications for carbon sequestration and redwood forest biodiversity. This is especially urgent given that some regions within the current redwood distribution in California (south of San Franscisco Bay) could become unsuitable for redwoods as soon as 2030.
To better understand redwood habitat suitability, a team of researchers from the University of Texas, Arizona State University, the University of Miami and Stanford University combined high-resolution redwood distribution maps with data on moisture availability to identify the environmental factors that shape redwood distribution. The study was published June 24 in Ecography. A coast redwood (Sequoia sempervirens) forest landscape at Mt. Tam in Marin County, California.Download Full Image
“Habitat suitability of coast redwood has been studied before, but not using high-resolution data at the landscape scale," said Emily Francis, lead author of the study. "The approach we employed here could be applied in other forest types to gain new insight into the role of moisture availability in landscape-scale patterns of habitat suitability for many tree species that may be vulnerable to climate change.”
The research was conducted in three redwood forests in California spanning approximately one-third of redwood latitudinal range. After analyzing spatial patterns in redwood distributions over more than 34,800 hectares (87,000 acres) across the three forests, the scientists found that redwood habitat suitability significantly varied in relation to moisture availability and fog across different landscape elevations. Redwood habitats were consistently more suitable at sites located closer to streams. The study also found that habitat suitability for redwoods ranged from 22%-75% within a single landscape, underlining the importance of considering landscape-scale variation while identifying sites that will continue to be suitable for redwoods, even as surrounding areas become inhospitable due to climate change.
“This study highlights the value of mapping the composition of our forests at high spatial resolution," said co-author Greg Asner, director of the ASU Center for Global Discovery and Conservation Science. "Doing so provides leverage to say something about the individual inhabitants within a forest, not just the forest as a blanket average. This, in turn, both enhances our knowledge and presents possible options for managing sensitive ecosystems undergoing climate change.”
The authors emphasized that predicting how climate change will impact future redwood distribution will require additional study to understand how both environmental and biological factors, such as tree seed dispersal and plant competition, will influence where redwoods are able to grow and survive.
This work was supported by the David and Lucile Packard Foundation, John D. and Catherine T. MacArthur Foundation, a Stanford Graduate Fellowship and Save the Redwoods League.
A team of astronomers has released the largest collection of sharp, detailed images of debris disks around young stars, showcasing the great variety of shapes and sizes of stellar systems during their prime planet-forming years. Surprisingly, nearly all showed evidence of planets.The images were obtained over a period of four years by a precision instrument, the Gemini Planet Imager (GPI), mounted...
Astronomers reveal new snapshots in time of the early stages of planet formation
June 24, 2020
A team of astronomers has released the largest collection of sharp, detailed images of debris disks around young stars, showcasing the great variety of shapes and sizes of stellar systems during their prime planet-forming years. Surprisingly, nearly all showed evidence of planets.
The images were obtained over a period of four years by a precision instrument, the Gemini Planet Imager (GPI), mounted on the 8-meter Gemini South telescope in Chile. GPI uses a state-of-the-art adaptive optics system to remove atmospheric blur, providing the sharpest images to date of many of these disks. These images, captured by the 8-meter Gemini South telescope using the Gemini Planet Imager, illustrate the variety of shapes and sizes that stellar systems can take during their infancy. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/T. Esposito (UC Berkeley)
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The large survey included stars with a range of ages; Patience designed the study of the youngest stars with ages of less than 20 million years. The young stars had indirect evidence of dusty disks but needed high-resolution imaging to reveal the structure of the dust.
“The new GPI images provide a snapshot in time of the early stages of planet formation, and our solar system may have resembled one of these systems early in its history,” Patience said.
Ground-based instruments like GPI, which is being upgraded to conduct similar observations in the northern sky from the Gemini North Telescope in Hawaii, can be a way to screen stars with suspected debris disks to determine which are worth targeting by more powerful, but expensive, telescopes to find planets — in particular, habitable planets. Several 20-, 30- and 40-meter telescopes, such as the Giant Magellan Telescope of which ASU is a founder, and the Extremely Large Telescope, will come online in the next couple of decades, while the orbiting James Webb Space Telescope is expected to be launched in 2021.
“It is often easier to detect the dust-filled disk than the planets, so you detect the dust first and then you know to point your James Webb Space Telescope or your Nancy Grace Roman Space Telescope at those systems, cutting down the number of stars you have to sift through to find these planets in the first place,” said lead author Tom Esposito, a postdoctoral fellow at the University of California, Berkeley.
Comet belts around other stars
The debris disks in the images are the equivalent of the Kuiper Belt in our solar system, a frigid realm about 40 times farther from the sun than Earth — beyond the orbit of Neptune — and full of rocks, dust and ice that never became part of any planet in our solar system. Comets from the belt — balls of ice and rock — periodically sweep through the inner solar system, occasionally wreaking havoc on Earth, but also delivering life-related materials like water, carbon and oxygen.
Of the 26 images of debris disks obtained by the GPI, 25 had “holes” around the central star that likely were created by planets sweeping up rocks and dust. Seven of the 26 were previously unknown; earlier images of the other 19 were not as sharp as those from GPI and often didn’t have the resolution to detect an inner hole. The survey doubles the number of debris disks imaged at such high resolution.
Animation of the solar system and moving outward to indicate stars observed with the Gemini Planet Imager mounted on the Gemini South telescope in Chile. Highlighted are the images of the dusty ringsencircling some of these young stars.
“One of the things we found is that these so-called disks are really rings with inner clearings,” said Esposito, who is also a researcher at the SETI Institute in Mountain View, California. “GPI had a clear view of the inner regions close to the star, whereas in the past, observations by the Hubble Space Telescope and older instruments from the ground couldn't see close enough to the star to see the hole around it.”
The GPI incorporates a coronagraph that blocks the light from the star, allowing it to see as close as one astronomical unit (AU) from the star, or the distance of the Earth from our sun: 93 million miles.
The GPI targeted 104 stars that were unusually bright in infrared light, indicating they were surrounded by debris reflecting the light of the star or warmed by the star. The instrument recorded polarized near-infrared light scattered by small dust particles, about a thousandth of a millimeter (1 micron) in size, likely the result of collisions among larger rocks in a debris disk.
"There has been no systematic survey of young debris disks nearly this large, looking with the same instrument, using the same observing modes and methods,” Esposito said. “We detected these 26 debris disks with very consistent data quality, where we can really compare the observations, something that is unique in terms of debris disk surveys.”
The seven debris disks never before imaged in this manner were among 13 disks around stars moving together though the Milky Way, members of a group called the Scorpius-Centaurus stellar association, which is located between 100 and 140 parsecs from Earth, or some 400 light-years.
“It is like the perfect fishing spot; our success rate was much greater than anything else we have ever done,” said co-author Paul Kalas, of the University of California, Berkeley. Because all seven are around stars that were born in the same region at roughly the same time, “that group itself is a mini laboratory where we can compare and contrast the architectures of many planetary nurseries developing simultaneously under a range of conditions, something that we really didn't have before,” Esposito added.
Of the 104 stars observed, 75 had no disk of a size or density that GPI could detect, though they may well be surrounded by debris left over from planet formation. Three other stars were observed to host disks belonging to the earlier “protoplanetary” phase of evolution.
What did our solar system look like in its infancy?
The extent of the debris disks varied widely, but most ranged between 20 and 100 AU. These were around stars that ranged in age from tens of millions of years to a few hundred million years, a very dynamic period for the evolution of planets. Most were larger and brighter than the sun.
The one star, HD 156623, that did not have a hole in the center of the debris disk was one of the youngest in the group, which fits with theories of how planets form. Initially, the protoplanetary disk should be relatively uniform, but as the system ages, planets form and sweep out the inner part of the disk.
“When we look at younger circumstellar disks, like protoplanetary disks that are in an earlier phase of evolution, when planets are forming, or before planets have started to form, there is a lot of gas and dust in the areas where we find these holes in the older debris disks,” Esposito said. “Something has removed that material over time, and one of the ways you can do that is with planets."
Because polarized light from debris disks can theoretically tell astronomers the composition of the dust, Esposito is hoping to refine models to predict the composition — in particular, to detect water, which is thought to be a condition for life.
“As we continue research into dusty disks around stars, the results from GPI will provide valuable benchmarks and comparisons for assessing planetary systems yet to be imaged,” co-author Hom said.
More than 100 researchers have contributed to GPI and the GPI Exoplanet Survey, and more than 35 were involved with the debris disk survey. The work was supported by the National Science Foundation (AST-1518332), National Aeronautics and Space Administration (NNX15AC89G) and Nexus for Exoplanet System Science (NExSS), a research coordination network sponsored by NASA’s Science Mission Directorate (NNX15AD95G). The NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory) operates the international Gemini Observatory, which is a facility of the U.S., Canada, Chile, Brazil, Argentina and South Korea.
This story was written by Robert Sanders of the University of California Berkeley with contributions from Karin Valentine, marketing and media relations manager with ASU’s School of Earth and Space Exploration.