PLANT FOSSILS AND OUR WORLD'S PAST

FROM:  NATIONAL SCIENCE FOUNDATION 

Tiny plant fossils offer window into Earth's landscape millions of years ago
Fossilized plant pieces tell a detailed story of our planet 50 million years ago
Minuscule, fossilized pieces of plants tell a detailed story of what Earth looked like 50 million years ago.

Researchers have discovered a way of determining density of trees, shrubs and bushes in locations over time--based on clues in the cells of plant fossils preserved in rocks and soil.

Tree density directly affects precipitation, erosion, animal behavior and a host of other factors in the natural world. Quantifying vegetation structure throughout time could shed light on how Earth's ecosystems have changed over millions of years.

"Knowing an area's vegetation structure and the arrangement of leaves on the Earth's surface is key to understanding the terrestrial ecosystem," says Regan Dunn, a paleontologist at the University of Washington's Burke Museum of Natural History and Culture. "It's the context in which all land-based organisms live, but we didn't have a way to measure it until now."

The findings are published in this week's issue of the journal Science.

New method offers window into distant past

"The new methodology provides a high-resolution lens for viewing the structure of ecosystems over the deep history of our planet," says Alan Tessier, acting director of the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research along with NSF's Division of Earth Sciences.

"This capability will advance the field of paleoecology and greatly improve our understanding of how future climate change will reshape ecosystems."

The team focused its fieldwork on several sites in Patagonia, which have some of the best preserved fossils in the world.

For years, paleontologists have painstakingly collected fossils from these sites and worked to precisely determine their ages using radiometric dating. The new study builds on this growing body of knowledge.

In Patagonia and other places, scientists have some idea based on records of fossilized pollen and leaves what species of plants were alive at given periods in history.

For example, the team's previous work documented vegetation composition for this area.

But there hasn't been a way to precisely quantify vegetation openness, aside from general speculations of open or bare habitats, as opposed to closed or tree-covered habitats.

"These researchers have developed a new method for reconstructing paleo-vegetation structure in open versus dense forests using plant biosilica, likely to be widely found in the fossil record," says Chris Liu, program director in NSF's Division of Earth Sciences.

"Now we have a tool to look at a lot of important intervals in our history where we don't know what happened to the structure of vegetation," adds Dunn, such as the period just after the mass extinction that killed the dinosaurs.

"Vegetation structure links all aspects of modern ecosystems, from soil moisture to primary productivity to global climate," says paper co-author Caroline Stromberg, a curator of paleobotany at the Burke Museum.

"Using this method, we can finally quantify in detail how Earth's plant and animal communities have responded to climate change over millions of years, vital for forecasting how ecosystems will change under predicted future climate scenarios."

Plant cell patterns change with sun exposure

Work by other scientists has shown that the cells found in a plant's outermost layer, called the epidermis, change in size and shape depending on how much sun it's exposed to while its leaves develop.

For example, the cells of a leaf that grow in deeper shade will be larger and curvier than the cells of leaves that develop in less covered areas.

Dunn and collaborators found that these cell patterns, indicating growth in shade or sun, similarly show up in some plant fossils.

When a plant's leaves fall to the ground and decompose, tiny silica particles inside the plants, called phytoliths, remain as part of the soil layer.

The phytoliths were found to represent epidermal cell shapes and sizes, indicating whether the plant grew in a shady or open area.

The researchers decided to check their hypothesis by testing it in a modern setting: Costa Rica.

Dunn took soil samples from sites in Costa Rica that varied from covered rainforests to open savannas to woody shrublands.

She also took photos looking directly up at the tree canopy (or lack thereof) at each site, noting the total vegetation coverage.

Back in the lab, she extracted the phytoliths from each soil sample and measured them under the microscope.

When compared with tree coverage estimated from the corresponding photos, Dunn and co-authors found that the curves and sizes of the cells directly related to how shady their environment was.

"Leaf area index" and plant cell structures compared

The researchers characterized the amount of shade as "leaf area index," a standard way of measuring vegetation over a specific area.

Testing this relationship between leaf area index and plant cell structures in modern environments allowed the scientists to develop an equation that can be used to predict vegetation openness at any time in the past, provided there are preserved plant fossils.

"Leaf area index is a well-known variable for ecologists, climate scientists and modelers, but no one's ever been able to imagine how you could reconstruct tree coverage in the past--and now we can," says co-author Richard Madden of the University of Chicago.

"We should be able to reconstruct leaf area index by using all kinds of fossil plant preservation, not just phytoliths. Once that is demonstrated, then the places in the world where we can reconstruct this will increase."

When Dunn and co-authors applied their method to 40-million-year-old phytoliths from Patagonia, they found something surprising--vegetation was extremely open, similar to a shrubland today. The appearance of these very open habitats coincided with major changes in fauna.

The paleobiologists plan to test the relationship between vegetation coverage and plant cell structure in other regions around the world.

They also hope to find other types of plant fossils that hold the same information at the cellular level as do phytoliths.

Paper co-authors are Matthew Kohn of Boise State University and Alfredo Carlini of Universidad Nacional de La Plata in Argentina.

In addition to NSF, the research was funded by the Geological Society of America, the University of Washington Biology Department and the Burke Museum.

-NSF-
Media Contacts
Cheryl Dybas, NSF

NSF PRESENTS FINDINGS FROM PAPER ON LARGE ANIMALS AND EFFECTS ON TROPICAL FORESTS

FROM:  THE NATIONAL SCIENCE FOUNDATION 

  Fruits of the forest gone: Overhunting of large animals has catastrophic effects on trees

As the animals go, so go tropical forests

The elephant has long been an important spiritual, cultural and national symbol in Thailand. At the beginning of the 20th century, its numbers exceeded 100,000.

Today, those numbers have plunged to 2,000. Elephants, as well as other large, charismatic animals such as tigers, monkeys and civet cats, are under attack from hunters and poachers.

Overhunting of animals affects entire forest

While the loss of these animals is concerning for species conservation, now researchers at the University of Florida have shown that overhunting can have widespread effects on the forest itself.

Overhunting leads to the extinction of a dominant tree species, Miliusa horsfieldii, or the Miliusa beech, with likely cascading effects on other forest biota.

The scientists report their results in the current issue of the journal Proceedings of the Royal Society B.

Co-authors of the paper are Trevor Caughlin and Jeremy Lichstein of the University of Florida and Doug Levey, formerly of the University of Florida and now a program director in the National Science Foundation's Division of Environmental Biology.

Other co-authors are researchers at King Mongkut's University of Technology Thonburi in Thailand, Wageningen University in the Netherlands and the Royal Thai Forest Department.

Loss of one tree species has far-reaching implications

The ecologists show how vital large animals are to maintaining the biodiversity of tropical forests in Thailand.

The team looked at how these mammals contribute to moving seeds through the forest.

"It's not surprising that seed dispersers help trees get to new places," says Levey. "The effects of hunting can extend far beyond the hunted, threatening the overall health of the trees that make up the forest."

Adds Caughlin, "On the surface, it doesn't seem that seed dispersal would be important for tree populations. But seed dispersal has an effect over the whole life of a tree."

Animals critical to seed transport through the forest

The scientists looked at the growth and survival of trees that sprouted from parent trees and grew up in crowded environs, compared to trees from seeds that were widely transported across the forest by animals.

The information was supplemented with a dataset from the Thai Royal Forest Department that contains more than 15 years of data on trees.

The researchers then created a long-term simulation and ran it on the University of Florida's supercomputer, the HiPerGator.

"Having that computing power was very important," says Caughlin, "because we had to simulate the fate of millions of seeds."

The scientists discovered that trees that grow from seeds transported by now-overhunted animals are hardier and healthier.

"Our study is the first to quantify the decades-long effects of animal seed dispersal across the entire tree life cycle, from seeds to seedlings to adult trees," says Lichstein.

Probability of tree extinction increased tenfold

The results show that loss of animal seed-dispersers increases the probability of tree extinction by more than tenfold over a 100-year period.

"The entire ecosystem is at risk," says Caughlin.

"We hope the study will provide a boost for those trying to curb overhunting," he says, "and provide incentives to stop the wildlife trade."

-- Cheryl Dybas, NSF
-- Gigi Marino, University of Florida

SCIENTIST STUDY GENETIC DIVERSITY IN OCEAN MICROBES

FROM:  NATIONAL SCIENCE FOUNDATION
Octillions of microbes in the seas: Ocean microbes show incredible genetic diversity

In a few drops of seawater, one species, hundreds of subpopulations
The smallest, most abundant marine microbe, Prochlorococcus, is a photosynthetic bacterial species essential to the marine ecosystem.

It's estimated that billions of the single-celled creatures live in the oceans, forming the center of the marine food web.

They occupy a range of ecological niches based on temperature, light, water chemistry and interactions with other species.

But the diversity within this single species remains a puzzle.

To probe this question, scientists at the Massachusetts Institute of Technology (MIT) recently performed a cell-by-cell genomic analysis of a wild population of Prochlorococcus living in a milliliter of ocean water--less than a quarter of a teaspoon--and found hundreds of distinct genetic subpopulations.

Each subpopulation in those few drops of water is characterized by a set of core gene alleles linked to a few associated flexible genes--a combination the scientists call the "genomic backbone."

This backbone gives the subpopulation a finely tuned ability to fill a particular ecological niche.

Diversity also exists within backbone subpopulations; most individual cells in the samples carried at least one set of flexible genes not found in any other cell in its subpopulation.

A report on the research by Sallie Chisholm and Nadav Kashtan at MIT, along with co-authors, appears in this week's issue of the journal Science.

The National Science Foundation (NSF), through its Divisions of Environmental Biology and Ocean Sciences, supported the research.

"In this extraordinary finding on the power of natural selection, the scientists have discovered a mosaic of genetically distinct populations of one of the most abundant organisms on Earth," says George Gilchrist, program director in NSF's Division of Environmental Biology.

"In spite of the constant mixing of the oceans," Gilchrist says, "variations in light, temperature and chemistry create unique habitats that evolution has filled with an enormous diversity of populations over millions of years."

Adds David Garrison, program director in NSF's Division of Ocean Sciences, "The results will change the way marine ecologists think about how planktonic microbes and, in turn, planktonic communities may respond to climate and environmental change."

The scientists estimate that the subpopulations diverged at least a few million years ago.

The backbone is an older, more slowly evolving, component of the genome, while the flexible genes reside in areas of the genome where gene exchange is relatively frequent, facilitating more rapid evolution.

The study also revealed that the relative abundance of the backbone subpopulations changes with the seasons at the study site near Bermuda, adding strength to the argument that each subpopulation is finely tuned for optimal growth under different conditions.

"The sheer enormity of diversity that must be in the octillion Prochlorococcus cells living in the seas is daunting to consider," Chisholm says. "It creates a robust and stable population in the face of environmental instability."

Ocean turbulence also plays a role in the evolution and diversity of Prochlorococcus.

A fluid mechanics model predicts that in typical ocean flow, just-divided daughter cells drift rapidly, placing them centimeters apart from one another in minutes, tens of meters apart in an hour, and kilometers apart in a week's time.

"The interesting question is, 'Why does such a diverse set of subpopulations exist?'" Kashtan says.

"The huge population size of Prochlorococcus suggests that this remarkable diversity and the way it is organized is not random, but is a masterpiece product of natural selection."

Chisholm and Kashtan say the evolutionary and ecological distinction among the subpopulations is probably common in other wild, free-living (not attached to particles or other organisms) bacteria species with large populations and highly mixed habitats.

Other co-authors of the paper are Sara Roggensack, Sébastien Rodrigue, Jessie Thompson, Steven Biller, Allison Coe, Huiming Ding, Roman Stocker and Michael Follows of MIT; Pekka Marttinen of the Helsinki Institute for Information Technology; Rex Malmstrom of the U.S. Department of Energy Joint Genome Institute and Ramunas Stepanauskas of the Bigelow Laboratory for Ocean Sciences.

The NSF Center for Microbial Oceanography, U.S. Department of Energy Genomics Science Program and the Gordon and Betty Moore Foundation Marine Microbiology Initiative also supported the work.

-NSF-

STUDY SHOWS ROCKY MOUNTAIN WILDFLOWER SEASON HAS LENGTHENED

FROM:  NATIONAL SCIENCE FOUNDATION 
Rocky Mountain wildflower season lengthens by more than a month

39-year bloom count reveals changes attributed to warmer climate
A 39-year study of wildflower blooms in a Colorado Rocky Mountain meadow shows that more than two-thirds of alpine flowers have changed their blooming patterns in response to climate change.

Not only are half the flowers beginning to bloom weeks earlier, but more than a third are reaching their peak blooms earlier, and others are producing their last blooms later in the year.

The blooming season, which used to run from late May through early September, now lasts from late April to late September, according to University of Maryland ecologist David Inouye.

The wildflower records, made up of more than two million blooms, suggest that flowering plants' responses to climate change are more complex than previously believed, with different species responding in unexpected ways.

The combinations of flowering species that bloom together are changing, too, with potential effects on insects and birds.

Studies that focus only on the date of flowers' first blooms--as most do--understate these changes, says Inouye, co-author of a paper published in this week's issue of the journal Proceedings of the National Academy of Sciences (PNAS).

"Long-term data are essential to understanding every environmental challenge the world faces," says Saran Twombly, a program director in the National Science Foundation's (NSF) Division of Environmental Biology, which funded the research.

"This study relies on long-term data to drive home the fact that species' responses to climate change are complex."

Phenology, the study of the timing of seasonal events, is crucial to knowing how climate change affects plants, animals and the relationships that bind them into natural communities.

To answer these questions, phenologists are collecting new data and poring through old records, such as amateur naturalists' notebooks.

"Most studies rely on first dates of events like flowering or migration because they use historical data sets that were not intended as scientific studies," Inouye says.

"First flowering is easy to observe. You don't have to take the time to count flowers. So that's often the only information available.

"It's taken a lot of effort to get the comprehensive insights needed for this analysis, which helps us understand how ecological communities may change in the future."

By counting blooms in each of 30 plots every other day, up to five months per year, for four decades, Inouye and colleagues amassed a data set including more than two million flowers.

For the study, University of Arizona biologist Paul CaraDonna, University of Maryland biologist Amy Iler and Inouye analyzed data on the 60 most common species.

Bloom times are changing fast, the researchers found.

The date the first spring flower appears has advanced by more than six days per decade over the course of the study.

The spring peak, when masses of wildflowers burst into bloom, has moved up by five days per decade.

And the last flower of fall occurred about three days later every decade. "The flowering season is about one month longer than it used to be," Iler says, "which is a big change for a mountain ecosystem with a short growing season."

Of all the species that have changed their flowering schedules in some way, only 17 percent shifted their entire bloom cycles earlier. The rest showed more complicated changes.

"First flowering isn't always the best predictor of all the changes we find," CaraDonna says.

"There's a lot more going on than you can get from this single, simple measure. So, it's important to take a closer look to understand all the ways climate change affects these wildflower communities."

As the plants' bloom patterns continue to change, researchers expect that some plants that bloomed simultaneously will no longer overlap, and others will start blooming together for the first time.

Ecologists refer to these new combinations as "'no-analog' communities."

"We usually think of no-analog communities as something that happens when plants or animals move into areas where they haven't lived before, creating novel combinations of species," Iler says.

"For example, we have red foxes at our study site now. It used to be too cold for them in winter. Now the marmots that live there have to deal with a new predator.

"But this study shows that even when species don't actually move, changes in the timing of key events in their life cycles may also result in no-analog communities, where species may interact differently than before."

The changes are likely to have a strong effect--for better or worse--on pollinating insects and migratory birds.

For example, Inouye says, hummingbirds that summer in the Rocky Mountains time their nesting so their eggs hatch at peak wildflower bloom, when there is plenty of flower nectar for hungry chicks.

But as the bloom season lengthens, the plants are not producing more flowers. The same number of blooms is spread out over more days, so at peak bloom there may be fewer flowers.

Will there be enough food for the hummingbirds' young?

To find out, Inouye plans to fit adult hummingbirds with radio transmitters to study how they interact with this summer's blooms.

-NSF-

WHERE IS THE GINSENG GOING? ANOTHER CHANGE IN THE NORTH AMERICAN FOREST

American Ginseng.  USFWS

FROM: NATIOAL SCIENCE FOUNDATION
The Stress of Being Ginseng
Being surrounded by ginseng--a low-growing green-leafed herb of North American forests--may have been common in 1751, but today? Ginseng is under siege.

Biologist James McGraw of West Virginia University should know. On World Environment Day, and indeed every day, McGraw says that we can learn much about the environment around us from one small plant.

Funded by a National Science Foundation (NSF) Long Term Research in Environmental Biology (LTREB) grant, McGraw and colleagues peer into the lives of more than 4,000 individual ginseng plants each year to see how they're faring.

"These understory plants are subject to all manner of [environmental] stresses," says McGraw. "After a while, you begin to wonder why there are any left."

Facing a panoply of threats

First, he says, there's harvesting for medicinal uses, "which is widespread and often illegally or at least unethically done. Then we have our four-footed friends--white-tailed deer--which eat a significant number of plants every year."

The plants' next challenge is the growth of invasive species such as multiflora rose and garlic mustard, which compete with ginseng.

The effects of global warming, including summers with heat waves and droughts, add to the burden for these plants of cooler climes. "Ginseng is also affected by ice storms, late frosts and hurricane flooding," says McGraw.

Then these Indiana Joneses of the plant world must survive what McGraw refers to as "natural pests:" insects defoliators and fungal pathogens.

Last--but definitely not least--is us.

"We're just beginning to understand what humans are doing to the forests where ginseng thrives: timbering, suppressing natural fires, mining, clearing land for housing developments, the list goes on and on," says McGraw.

The persistence of a slow-growing and valuable medicinal plant "despite all this," he says, "is a testament to the resilience of nature--and to the stewardship of those land-owners who care about protecting biodiversity in their forests."

Species in an extinction vortex

Tigers, elephants and ginseng all share a common feature, says Saran Twombly, director of NSF's LTREB program.

"These dwindling populations face increasing threats that trap them in an extinction vortex," Twombly says.

"McGraw's research relies on long-term data to identify the factors threatening populations of this important forest plant. The results show the knife-edge that separates healthy and unhealthy populations."

The NSF LTREB award "has been critical to our understanding of the 'big picture' of ginseng conservation," says McGraw.

He and colleagues work on one species of ginseng, Panax quinquefolius L., American ginseng.This member of the ginseng family, whose genus name Panax means "all heal" in Greek, hides deep in eastern deciduous woodlands.

The plant was historically found in rich, cool hardwood forests--from southern Quebec and Ontario south to northern Georgia, and west as far as Minnesota, eastern Oklahoma and northern Louisiana.

"Ginseng populations vary from frequent to uncommon to rare across the landscape," says McGraw, "but they're almost always small, usually fewer than 300 plants."

Medicinal plant for the ages

The species has long been valued for its medicinal qualities, especially by Asian cultures. They've integrated American ginseng into traditional medicinal practices as a complement to native Asian ginseng species.

In Asia, ginseng is considered an adaptogen--it enhances overall energy levels.

"In western medicine, ginseng has exhibited anti-cancer properties in cell cultures," says McGraw. "It's also shown beneficial effects on blood sugar and obesity, as well as on enhancing the immune system for prevention of colds and flu."

After ginseng was discovered in North America, the market quickly became profitable enough to fuel intense wild harvesting, eventually reaching an industrial scale.

"Ginseng shares a part of early American history," says McGraw. "Its roots--the most sought-after parts--were first exported to Asia from the United States in the early 1700s."

In one typical year (1841), more than 290,000 kilograms of dry ginseng roots were shipped from North America to the Asian continent.

"Although average root size was larger in the 1800s than it is today," says McGraw, "even a conservative estimate suggests that this represents at least 64 million roots."

Ginseng at the forefront

Harvest of the plant has continued apace, he says, particularly in the Appalachian region, where the sale of ginseng still supplements household incomes.

Ecologists began studying ginseng because of its value as a wild-harvested species, and its decrease in abundance after decades of harvesting.

Now, however, ginseng has become an important model species--a sensitive indicator of the effects of global and regional environmental change on deciduous forests.

"The prominence of American ginseng has led to its use as a 'phytometer' [a gauge] to better understand how change is affecting lesser-known plant species in eastern North America," says McGraw.

The data in his project come from 30 ginseng populations in seven states. "Our study populations are in habitats from suburban woodlots to rich, old-growth forests," McGraw says.

In a paper published this year in the Annals of The New York Academy of Sciences, McGraw and co-authors state that the Asian market has made ginseng North America's most important harvested wild medicinal plant over the past two centuries.

That status prompted a listing on CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) Appendix II. All species on Appendix II are susceptible to extinction in the absence of trade controls.

Most states with ginseng populations are converging on a uniform start date for harvesting--Sept. 1. "That allows time after harvest for planting ripe seeds that will lead to recovery of the plants," McGraw says.

Since forests are, for the most part, open to everyone, ginseng will continue to be harvested as long as there is immediate profit to be made, scientists believe.

Successful sustainability in such open access habitats, they say, depends on management of the resource by those who actively harvest it.

Sustainability and ginseng

McGraw and colleagues' research shows that ginseng harvesters willing to employ a stewardship strategy gain the most benefit by harvesting when seeds are ripe, usually in autumn months, then planting the seeds to ensure high germination rates.

September is a summertime away. But in northeastern forests, ginseng leaves have already unfurled.

"Now they face a gamut of environmental challenges," says McGraw. "They're rooted in place, left with whatever nature--or more likely humans--dish out. If we want ginseng to be part of the future landscape, we had best tread very carefully."

"Ginseng is not everywhere common," wrote Swedish naturalist Peter Kalm in 1749. "Sometimes you may search the woods for several miles without finding a single plant. Round Montreal they formerly grew in abundance, but there is not a single plant to be found, so they have been rooted out."

By three centuries later, northeastern forests may be empty--at least of an unassuming and "all healing" herb named ginseng.