This means just a few towering white fir, sugar pine and incense cedars per acre at the Yosemite site are disproportionately responsible for photosynthesis, converting carbon dioxide into plant tissue and sequestering that carbon in the forest, sometimes for centuries, according to James Lutz, a University of Washington research scientist in environmental and forest sciences. Lutz is lead author of a paper on the largest quantitative study yet of the importance of big trees in temperate forests being published online May 2 on PLoS ONE. The research was funded by the Smithsonian Center for Tropical Forest Science.

Image right: A handful of large-diameter trees per acre, such as these incense cedars, together with remains of big trees like the three-foot-wide white fir snag and downed debris account for half the forest biomass at a Yosemite National park study site. (Image by James Lutz)

“In a forest comprised of younger trees that are generally the same age, if you lose one percent of the trees, you lose one percent of the biomass,” he says. “In a forest with large trees like the one we studied, if you lose one percent of the trees, you could lose half the biomass.”

In 2009, scientists including Lutz reported that the density of large-diameter trees declined nearly 25 percent between the 1930s and 1990s in Yosemite National Park, even though the area was never logged. Scientists have found notable numbers of large trees dying in similar areas across the West.

The new 63-acre study site is one of the largest, fully-mapped plots in the world and the largest old-growth plot in North America. The tally of what’s there, including the counting and tagging of 34,500 live trees, was done by citizen scientists. The site is part of the network of the Smithsonian Center for Tropical Forest Science, a global network of 42 tropical and temperate forest plots including the one in Yosemite.

Image left: Washington State University’s Mark Swanson pulls a tape tight around a 4-foot-wide sugar pine, one of the 34,500 live trees counted and tagged for long-term study in a Yosemite National Park study plot. (Washington State University)

One implication of the research is that land managers may want to pay more attention to existing big trees, the co-authors said. In some younger forests that lack big trees, citizens and land managers might want to consider fostering the growth of a few big-trunked trees, Lutz added.–Source: University of Washington.

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CTFS-SIGEO is a global network of forest research plots committed to the study of tropical and temperate forest function and diversity. The multi-institutional network includes plots across the Americas, Africa, Asia, and Europe, with a strong focus on tropical regions. Ecologists at the Smithsonian Tropical Research Institute established the first forest dynamics plot on Barro Colorado Island in the Panama Canal in 1980.

Image left: Daniel Johnson, a biology graduate student at Indiana University, measures the diameter of a white ash tree in the University’s Lilly-Dickey Woods. The 550-acre woods were recently added to CTFS-SIGEO’s global network of forest research plots. (Photo by F. Collin Hobbs)

Stuart J. Davies, CTFS-SIGEO director and senior staff scientist at the Smithsonian Tropical Research Institute, will make the move along with David Kenfack, CTFS-SIGEO Africa Program coordinator. Davies sees the need for increased presence at the Smithsonian in Washington, D.C. as the network continues to build partnerships within different Smithsonian units.

The scale and intensity of the CTFS-SIGEO research program remains unprecedented in forest science. Scientists monitor the growth and survival of about 4.5 million trees of approximately 8,500 species in 21 different countries. The work aims to increase the scientific understanding of forest ecosystems, guide sustainable forest management and natural-resource policy, monitor the impacts of climate change, and build capacity in forest science. Most recently CTFS-SIGEO added the Lilly-Dickey Woods–a 550-acre forest in Brown County Indiana that is a research and teaching preserve for Indiana University–to its network of forest research plots.

Because of its extensive biological monitoring, unique databases, and the expertise of its partners, CTFS-SIGEO enhances society’s ability to evaluate and respond to the impacts of global climate change. Monitoring so many forest plots at once is providing a comprehensive, yet locally detailed perspective on how the world’s forests are being transformed by global change.  Research on tropical forest dynamics continues, but is joined by new initiatives studying carbon fluxes, temperate forests, ecosystem services, and biodiversity. CTFS-SIGEO and its many institutional partners are leveraging huge intellectual horsepower to transform our understanding of forest-ecosystem structure and function. The network has been so successful that the Smithsonian is now planning to extend its system of earth observatories to the near shore marine realm. –Source: The Plant Press, newsletter of the Department of Botany, National Museum of Natural History.

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Jonathan Thompson is Research Ecologist at the Smithsonian Conservation Biology Institute, Research Associate at the Harvard Forest, and lead author on the paper which appeared in the journal Ecological Applications in late 2011. “The rebounding forests of New England provide a tremendous public benefit by storing carbon that would otherwise contribute to climate change,” said Thompson. To put these findings into context he adds, “In Massachusetts, forests capture approximately 2.3 million metric tons of carbon each year. That’s equal to the amount of carbon dioxide emitted from the energy used by one million American homes annually.” He and his coauthors were able to estimate the extent to which development may chip away at that carbon sink, using an uncommon collection of long-term data and a distinct form of research known as scenario science.

Image right: From this 71-foot eddy-flux tower in a 200-year-old hemlock forest, Harvard Forest scientists have measured carbon dynamics and other ecosystem processes for more than 20 years as part of the Long-Term Ecological Research program. Located in a 35-hectare Smithsonian Global Earth Observatory plot and part of the core measurements for the National Ecological Observatory Network, this tower is a focal point for studies of the eastern hemlock tree and its impending demise from the invasive hemlock wolly adelgid, as well as phenology studies of succeeding hardwoods.
(Photos by David Foster)

For more than 30 years, scientists at the Harvard Forest have scaled towers into the forest canopy and measured the trunks of trees to track how much carbon is stored or lost from the woods each year. This treasure trove of data is part of the national Long-Term Ecological Research (LTER) Network, which is celebrating more than three decades of research this month. This important milestone is marked by six new papers released today in a special issue of the journal BioScience. The forest carbon research is one example of participatory scenario science — a growing trend in ecology featured in a paper by Thompson, David Foster, Director of the Harvard Forest, and their colleagues in the BioScience issue.

Image left: Summer Research Program students monitor soil respiration of decaying wood in a large study comparing carbon, water, and energy fluxes between harvested and unharvested sites.

Harvard Forest is one of four LTER sites in the northeastern U.S. and was awarded a grant by the National Science Foundation to join the Network in 1988. David Foster coauthored the Ecological Applications paper of 2011 and co-edited the new BioScience special issue. He notes, “With three decades of data meticulously collected as part of the LTER Network, we have reached a crucial transition where we are now able to tackle major environmental challenges, such as the fate of forest carbon, across large landscapes.”

Foster adds, “Over the last two centuries, forests have stored more carbon with each passing year in many parts of New England, but the turning point may be in sight for Massachusetts and other urbanizing landscapes if recent development trends continue.” But that’s not the end of the story for Foster: “The good news is that forests are resilient and history is not necessarily destiny. Our research makes a compelling case for expanding support for forestland protection and for the efforts of private landowners to keep their land forested. It reminds us that forests provide important infrastructure that we should invest in, just as we do major civil works projects.”

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Image left: SERC scientist João Canning Clode observes a green porcelain crab in his laboratory at the Smithsonian Environmental Research Center.

But what happens to these fair-weather travelers during a severe cold snap, such as the one that occurred in January 2010 across much of the southeastern and eastern United States? To investigate, Smithsonian Environmental Research Center scientist João Canning Clode and colleagues at the Environmental Research Center in Edgewater, Md., tested the cold-water tolerances of invasive green porcelain crabs (Petrolisthes armatus) in their laboratory. Crabs were collected in Georgia and brought to the lab where they were subjected to one of three temperature treatments. The first was a control treatment of constant moderate winter temperature. The second was treatment in which the temperature was dropped to mimic the cold snap of January 2010, and the third treatment consisted of the extreme cold temperatures of a severe winter.

Canning-Clode and his colleagues found that most of the crabs in the control treatment survived (83%), but many of the crabs in the second cold treatment (61%) and all of the crabs in the third extreme cold treatment (100%) died. Crabs that survived cold treatment number two were sluggish, possibly making them more susceptible to predation and impacting their ability to feed, the scientists determined.

The scientists determined that prolonged exposure to cold temperatures also may compromise the green porcelain crab’s ability to overcome cumulative cold events, such as the two other record cold snaps that occurred in February and March of 2010.

Image right: A green porcelain crab (Photo by Juan Antonio Baeza)

The loss of more than 60% of their population during each cold period might explain the recent dramatic decline of the green porcelain crab in Georgia in 2010, suggesting that extreme cold spells may limit or prevent the northward spread of this invasive species.

Several climate models used to predict how species will react to climate change in the next 100 years have projected a continued decline of global biodiversity and increased spread of introduced species. Many of these models focus on temperature increases, but few have evaluated the impact of severe weather like cold snaps, Canning-Clode and his colleagues write in a paper on their study recently published at PLoS ONE.

For Canning Clode “the core message of this paper is that yes, climate change is happening, but cold is also part of this change. We believe these periodic cold events will limit the range expansion of Petrolisthes armatus as well as other Caribbean creep species” –Monaca Noble, SERC

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Image right: The Smithsonian’s Barro Colorado Island was the site of the first large-scale, long-term forest dyanmics plots. Now there are 42 forest dynamics plots worldwide that use the same methodology, the Smithsonian Institution Global Earth Observatory system managed by the Center for Tropical Forest Science. (Photo by Marcos Guerra)

“Air pollution is fertilizing tropical forests with one of the most important nutrients for growth,” said S. Joseph Wright, staff scientist at the Smithsonian Tropical Research Institute in Panama. “We compared nitrogen in leaves from dried specimens collected in 1968 with nitrogen in samples of new leaves collected in 2007. Leaf nitrogen concentration and the proportion of heavy to light nitrogen isotopes increased in the last 40 years, just as they did in another experiment when we applied fertilizer to the forest floor.”

Nitrogen is an element created in stars under high temperatures and pressures. Under normal conditions, it is a colorless, odorless gas that does not readily react with other substances. Air consists of more than 75% nitrogen. But nitrogen also plays a big role in life as an essential component of proteins. When nitrogen gas is zapped by lightning, or absorbed by soil bacteria called “nitrogen fixers,” it is converted into other “active” forms that can be used by animals and plants. Humans fix nitrogen by the Haber process, which converts nitrogen gas into ammonia—now a principal ingredient in fertilizers. Today, nitrogen fixation by humans has approximately doubled the amount of reactive nitrogen emitted.

Image left: The Smithsonian’s Barro Colorado Island was the site of the first large-scale, long-term forest dyanmics plots. Now there are 42 forest dynamics plots worldwide that use the same methodology, the Smithsonian Institution Global Earth Observatory system managed by the Center for Tropical Forest Science. (Photo by Marcos Guerra)

Nitrogen comes in two forms or isotopes: atoms that have the same number of protons but different numbers of neutrons. In the case of nitrogen, the isotopes are ¹⁴N and ¹⁵N, although only about one in 300 nitrogen atoms is the heavier form. Imagine nitrogen in the ecosystem like a bowl of popcorn. Normally the ratio of popped (light) to unpopped (heavy) kernels stays the same, but when someone starts to eat the popcorn, the lighter, popped kernels get used up first, increasing the ratio of heavy to light kernels (or ¹⁵N/¹⁴N in the case of the ecosystem). Light nitrogen is lost through nitrate leaching and as gases such as N2, and various forms of nitrous oxides or “noxides,” some of which can be important greenhouse gases. In the fertilization study in Panama, mentioned earlier, N₂O emissions were tripled.

“Tree rings provide a handy timeline for measuring changes in wood nitrogen content,” said Peter Hietz from the Institute of Botany at the University of Natural Resources and Life Sciences in Vienna, who faced down a tiger when sampling trees in a monsoon forest on the Thailand-Myanmar border. “We find that over the last century, there’s an increase in the heavier form of nitrogen over the lighter form, which tells us that there is more nitrogen going into this system and higher losses. We also got the same result in an earlier study of tree rings in Brazilian rainforests, so it looks like nitrogen fixed by humans now affects some of the most remote areas in the world.”

“The results have a number of important implications,” said Ben Turner, staff scientist at STRI. “The most obvious is for trees in the bean family (Fabaceae), a major group in tropical forests that fix their own nitrogen in association with soil bacteria. Increased nitrogen from outside could take away their competitive advantage and make them less common, changing the composition of tree communities.”

“There are also implications for global change models, which are beginning to include nitrogen availability as a factor affecting the response of plants to increasing atmospheric carbon dioxide concentrations,” said Turner. “Most models assume that higher nitrogen equals more plant growth, which would remove carbon from the atmosphere and offset future warming. However a challenge for the models is that there is no evidence that trees are growing faster in Panama, despite the long-term increases in nitrogen deposition and atmospheric carbon dioxide.”

Decades of atmospheric nitrogen deposition have caused major changes in the plants and soils of temperate forests in the U.S. and Europe. Whether tropical forests will face similar consequences is an important question for future research.

The Smithsonian Tropical Research Institute, headquartered in Panama City, Panama, is a unit of the Smithsonian Institution. The Institute furthers the understanding of tropical nature and its importance to human welfare, trains students to conduct research in the tropics and promotes conservation by increasing public awareness of the beauty and importance of tropical ecosystems. Website: www.stri.org.

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The dodo’s large size and inability to fly were adaptations that allowed this bird to survive some of the most hostile conditions and climactic events imaginable. Only in the 1600s did a force more deadly than extreme drought and volcanic eruptions lead to its extinction: humans.

Image right: Painting of a dodo head by Cornelis Saftleven. Done in 1638,  this painting may be one of the last illustrations made of a live dodo. (Image from Boijmans Museum, Rotterdam)

In a recent paper in the journal “The Holocene” a team of scientists detail the extreme conditions that caused the death of some 500,000 animals on Mauritius during the mid-Holocene at around 4000 years ago. The evidence is a thick bed of fossil bones on Mauritius that spans an area of about 5 acres—the site of a former freshwater lake bed. The fossil layer is dominated by the remains of thousands of dodos and giant tortoises, as well as many small reptiles and flying birds.

Image left: Dodo bone in a matrix of mud, seed and other fossils excavated in a dry lake bed on the Island of Mauritius. (Image copyright Kenneth Rijsdijk/Dodo Research Programme)

Using radiocarbon dating of the bones, oxygen isotope analysis of geologic features on Mauritius and nearby islands, and the study of the island’s water table, the scientists determined the animals died during an extreme drought that lasted several decades. “Dodos, tortoises, lizards and other animals gathered here because the lake was one of the few sites on the island with fresh water,” says Hanneke Meijer, an ornithologist at the Smithsonian’s National Museum of Natural History and one of the paper’s co-authors.

“It is evident that a lot of animals suffered and died during this period, and their populations were greatly reduced,” Meijer continues, “but no species, including the dodo, went extinct during this extreme drought.” Fossil evidence reveals that “all animals were still living and the island’s ecosystem was intact at the time humans arrived in the 1600s.”

Image right: The excavation site on the island of Mauritius where the remains of some 500,000 animals were found, victims of an extreme drought some 4,000 years ago. (Image copyright Mikel Rijsdijk/Dodo Research Programme)

The dodo was resilient, and perfectly adapted to the island’s habitat, Meijer explains. “The island had no predators or carnivores and the dodo had no need to flee, so it lost its ability to fly. It received a reputation as stupid because it did not flee from humans” and human-introduced predators after they arrived at the dodo’s home in the 1600s.

Today, Meijer says, the forest cover on Mauritius has been reduced by 98 percent with only a few patches of original forest remaining. Considerable resources have been directed to preserving the island’s few remaining endemic species, such as the Mauritian kestrel. (The island’s giant tortoises went extinct in the 1800s when Dutch trade ships filled their holds with these long-lived animals to use as fresh meat on long voyages to and from Indonesia. “Mauritius was a popular stop because it provided fresh water and lots of food,” Meijer says)

Image left: Researchers at the Mauritius Island excavation site sieving excavated mud for small bones, teeth and plant remains. (Image copyright Mikel Rijsdijk/Dodo Research Programme)

Should another extended drought occur similar to the mid-Holocene event, it is very likely the remaining endemic species on Mauritius would not survive as the environment is so degraded. “Even many of the native plant species in the few remaining forest patches would probably perish,” Meijer says.

“With modern climate change scientists are very interested in how island animals adapt, as their ability to move to less disturbed areas is limited,” Meijer explains. “It has always been thought that animals on islands are particularly sensitive to climate change.” In the case of the dodo and other species on Mauritias, this new study reveals an island population highly resilient to climate change.

The article “Mid-Holocene (4200 kyr BP) mass mortalities in Mauritius (Mascarenes): Insular vertebrates resilient to climatic extremes but vulnerable to human impact,” appeared recently in the scientific journal “The Holocene.” (Rijsdijk, K.F., Zinke, J., de Louw, P.G.B., Hume,J.P., van der Plicht, J., Hooghiemstra, H., Meijer, H.J.M., Vonhof, H.B., Porch, N., Florens, F.B.V., Baider, C., van Geel, B., Brinkkemper, J., Vernimmen, T. & Janoo, A., 2011. Mid-Holocene (4200 kyr BP) mass mortalities in Mauritius (Mascarenes): Insular vertebrates resilient to climatic extremes but vulnerable to human impact. The Holocene, doi:10.1177/0959683611405236)

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Images left and below: The variation in biodiversity from place to place, called beta diversity, are actually very similar as you move from the tropics to the poles when you account for the number of species present in the first place. (Photos by Christian Ziegler)

“The same ecological processes seem to be working worldwide. The difference is that tropical organisms have been accumulating for vast periods of time,” said Nathan J.B. Kraft, post-doctoral fellow at the University of British Colombia, who led the research team.

“This study shows how collecting data using the same methods at sites around the world, similar to what we do at the Center for Tropical Forest Science–Smithsonian Institution Global Earth Observatories Network, offers new insights into the processes that shape ecological communities,” said Comita, formerly a post-doctoral fellow at the National Center for Ecological Analysis and Synthesis, now an assistant professor at The Ohio State University. “We found that measurements of variation in biodiversity from place to place, called beta diversity, are actually very similar as you move from the tropics to the poles when you account for the number of species present in the first place.”

Forests in Canada and Europe may have much more in common with tropical rainforests than previously believed. “We see that biodiversity patterns can be explained not by current ecological processes, unfolding over one or two generations, but by much longer-term historical and geological events,” said Kraft, who will join the faculty at the University of Maryland next year.

“Fossils tell a similar story,” said STRI scientist, Aaron O’Dea, co-author, with Willem Renema and others, of a 2008 article in Science showing that marine biodiversity hotspots could be traced back to ancient areas of tectonic activity. “Geological history reveals that glaciations and mass extinctions have lasting effects on the structure of biological communities. It bears witness to the devastation that occurs when accumulated biodiversity is lost: a threat we are facing today.”

The team, which also included researchers from institutions in the U.S., Canada and New Zealand, was supported by the U.S. National Center for Ecological Analysis and Synthesis and the U.S. National Science Foundation.–Beth King, Smithsonian Tropical Research Institute

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The research was led by scientists from the Centre for Ecology and Hydrology and the University of Cambridge, UK. The results were published online today in the scientific journal “Nature Climate Change.”

Image right: Leaf litter around the buttress roots of a tropical tree at the study site in Panama.

The researchers used results from a six-year experiment in a rainforest at the Smithsonian Tropical Research Institute in Panama, to study how increases in litterfall–dead plant material such as leaves, bark and twigs which fall to the ground–might affect carbon storage in the soil. Their results show that extra litterfall triggers an effect called ‘priming’ where fresh carbon from plant litter provides much-needed energy to micro-organisms, which then stimulates the decomposition of carbon stored in the soil

Lead author Emma Sayer from the Smithsonian Tropical Research Institute and the Centre for Ecology and Hydrology said, “Most estimates of the carbon sequestration capacity of tropical forests are based on measurements of tree growth. Our study demonstrates that interactions between plants and soil can have a massive impact on carbon cycling. Models of climate change must take these feedbacks into account to predict future atmospheric carbon dioxide levels.”

Image left: Undergrowth showing leaf litter at the Smithsonian Tropical Research Institute study site. (Photos by Emma Sayer)

The study concludes that a large proportion of the carbon sequestered by greater tree growth in tropical forests could be lost from the soil. The researchers estimate that a 30% increase in litterfall could release about 0.6 tonnes of carbon per hectare from lowland tropical forest soils each year. This amount of carbon is greater than estimates of the climate-induced increase in forest biomass carbon in Amazonia over recent decades. Given the vast land surface area covered by tropical forests and the large amount of carbon stored in the soil, this could affect the global carbon balance

Tropical forests play an essential role in regulating the global carbon balance. Human activities have caused carbon dioxide levels to rise but it was thought that trees would respond to this by increasing their growth and taking up larger amounts of carbon. However, enhanced tree growth leads to more dead plant matter, especially leaf litter, returning to the forest floor and it is unclear what effect this has on the carbon cycle.

“Soils are thought to be a long-term store for carbon but we have shown that these stores could be diminished if elevated carbon dioxide levels and nitrogen deposition boost plant growth,” Sayer adds.

Co-author Edmund Tanner, from the University of Cambridge, said, “This priming effect essentially means that older, relatively stable soil carbon is being replaced by fresh carbon from dead plant matter, which is easily decomposed. We still don’t know what consequences this will have for carbon cycling in the long term.” –Source: Center for Ecology and Hydrology

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