Many birds are arriving earlier each spring as temperatures warm along the East Coast of the United States.  However, the farther those birds journey, the less likely they are to keep pace with the rapidly changing climate.

Scientists at Boston University and the Manomet Center for Conservation Sciences analyzed changes in the timing of spring migrations of 32 species of birds along the coast of eastern Massachusetts since 1970.  Researchers at Manomet gathered this data by capturing birds in mist nets, attaching bands to their legs, and then releasing them.  Their findings, published in Global Change Biology, show that eight out of 32 bird species are passing by Cape Cod significantly earlier on their annual trek north than they were 38 years ago.  The reason?  Warming temperatures.  Temperatures in eastern Massachusetts have risen by 1.5 degrees Celsius (2.7 degrees Fahrenheit) since 1970.

Species, such as the swamp sparrow, that winter in the southern United States are generally keeping pace with warming temperatures and earlier leafing of trees.  They migrate earlier when temperatures are warm and later when spring is cool.

Birds that winter further south, like the great crested flycatcher, which spends its winters in South America, are slow to change, though.  Their migration times are not changing, despite the warming temperatures in New England.

There appears to be good reason for the difference between the shortand long-distance migrants.  Because temperatures are linked along much of the East Coast of the United States—an early spring in North Carolina is generally an early spring in Massachusetts—the short-distance migrants can gain insight into when it will be warm further north.  They can follow the flush of leaves and insects all the way to their breeding grounds each year.  Long-distance migrants, though, do not have any good cue for whether it will be an early or late spring on the northern stretches of their migrations.  Weather in South America has little to do with weather in New England.

Being slow to change in response to warming temperatures could have serious repercussions for long-distance migrant birds.  This same research group has shown that plants are blooming earlier in Massachusetts than they did in the past.  It appears that the short-distance migrants are keeping pace with this changing environment.  However, long-distance migrants are being left behind; as temperatures continue to warm, they will probably experience environments increasingly different from the ones for which they are adapted.  Other researchers have already noted that some long-distance migrant birds returning from African wintering areas to breed in Europe are now mistimed with their insect food supply.  The inability of some birds to adapt to rapid climate change may be an important factor in some of the declines among songbird populations that have been documented in recent years.

To investigate the origins of vertebrates and other features of cephalochordate biology, a team of researchers led by Dr. Linda Holland of the Scripps Institution of Oceanography searched the amphioxus genome for specific genes, gene families, and DNA elements that could shed light on chordate biology and evolution. The analysis identified a number of features of amphioxus that are conserved with vertebrates, as well as some that are unique. In addition to new insights on development, cell signaling, immunity, and endocrine systems, Holland and colleagues identified several DNA regulatory elements conserved between amphioxus and humans. Three conserved elements from two human paralogs and a single amphioxus homolog were all shown to drive gene expression in both amphioxus and the mouse. “This is the widest phylogenetic distance to date over which both the sequence and function of cis-regulatory enhancers has been found to be conserved,” explains Holland. The group concluded that while amphioxus displays many characteristics of a pre-vertebrate ancestor, it also has specialized features that have developed since diverging from chordate ancestors.

Huge numbers of fish, seabirds, and other marine animals are routinely killed and discarded after being inadvertently caught during fishing operations. Known as marine bycatch, this problem is an ongoing challenge to the fishing industry, regulatory agencies, and conservationists. One recent proposal would compensate for bycatch by reducing other impacts on affected species, but a new analysis suggests that this strategy could end up doing more harm than good.A paper published last year in Frontiers in Ecology and the Environment made the case for “compensatory mitigation” of fisheries bycatch, using seabird deaths caused by a longline fishery as an example. The authors suggested that eradicating rats from an island with seabird nesting colonies could have more benefits for a population of shearwaters than efforts to reduce bycatch in the longline fishery.

A number of seabird experts, however, were skeptical of the paper’s findings. Given its potential influence on fishery policies, they decided the proposal warranted a careful evaluation.

“There are so many complexities involved in fisheries bycatch, we felt compelled to thoroughly examine the strengths and weaknesses of this approach and establish the criteria that would have to be met for it to work,” said Myra Finkelstein, a postdoctoral fellow in ecology and evolutionary biology at the University of California, Santa Cruz.

Finkelstein is the lead author of a paper published June 18 in the journal PLoS ONE that evaluates the potential effectiveness of compensatory mitigation for marine bycatch. She worked with a dozen coauthors whose areas of expertise include seabird conservation and ecology, marine bycatch, and mathematical modeling of wildlife populations. The researchers concluded that compensatory mitigation could only rarely succeed in reducing or offsetting the effects of marine bycatch.

“It’s very difficult to make this work,” Finkelstein said. “Most of the species threatened by bycatch evolved to live long and reproduce slowly. When bycatch kills adults, these populations just aren’t capable of making up for it through increased reproduction. It really is about the bycatch.”

Another major stumbling block is that bycatch typically involves a large variety of nontarget species, whereas compensatory mitigation actions are likely to affect only one or a few of those species.

“Marine bycatch is not a single-species problem,” Finkelstein said. “So many nontarget species are caught in a given fishery that mitigating the effects on one species could lead to a bigger impact on other species.”

The researchers also found flaws in the case study of flesh-footed shearwaters used to support the compensatory mitigation strategy in the original paper. But the bulk of the new paper is devoted to a set of five criteria for evaluating any proposals to implement such strategies. The researchers found that compensatory mitigation for marine bycatch is likely to be successful only in a limited number of situations. In many cases, they said, it has the potential to accelerate declines of marine species currently threatened by fisheries bycatch.

“These are complicated situations. We have to be very cautious, especially with critically endangered species, before we adopt a policy that allows continued mortality from bycatch,” Finkelstein said.

The United Nations Framework Convention on Climate Change is currently discussing ways of Reducing Emissions from Deforestation and Degradation (REDD) in developing countries. REDD has great potential to deliver benefits for biodiversity and people, as well as for the climate.

However, it is likely that these benefits will be concentrated in forests with high carbon stocks and that land use change may shift to low-carbon forests and other ecosystems important for biodiversity.

Dr Lera Miles, lead author and Acting Head of the Climate Change and Biodiversity Programme at the United Nations Environment Programme World Conservation Monitoring Centre (WCMC), said: “Land use change, mostly deforestation, accounts for 18-25% of global annual greenhouse gas emissions. We support the initiative to conserve forests, which will help to address this growing problem as well as maintain valuable habitats; however, we are concerned about potential unintended negative impacts on some ecosystems.

“If forests are protected through REDD without addressing the underlying causes of forest clearance, such as increasing demand for food, then some clearance of natural ecosystems will simply shift to other areas and different habitats will be destroyed. ”

Dr Miles and her colleague and co-author of the paper Dr Valerie Kapos, Visiting Fellow at the University of Cambridge and Senior Advisor at UNEP-WCMC, suggest that a shift in the focus of conservation investment may be needed to counteract these potential side effects of REDD. Increased conservation focus may be needed on forests with lower carbon density, which would be less valuable in carbon terms, but still rich in biodiversity, and on non-forest ecosystems such as savannahs, grasslands and wetlands, which would also be under increased pressure.

Dr Kapos said: “Currently, much conservation investment is focused on species-rich tropical forests. A successful REDD mechanism would direct far more funds to tropical forests than are currently available for biodiversity conservation. We suggest that in such a scenario, strategies for conservation investment will need urgent re-thinking.

“The climate change convention has agreed to a trial period for testing approaches to REDD, which presents an important opportunity to assess the magnitude of potential unintended impacts. Conservation scientists and practitioners need to assess the potential consequences of REDD for biodiversity, and to communicate clearly their findings. Decision-makers will need to take these findings into account as REDD evolves towards a global agreement.”

Two papers published in the journal Science today* by Microsoft Research ecologist Drew Purves together with research colleagues at Princeton University and universities in Madrid, Spain, highlight how an improved understanding of forest dynamics is needed to better predict environmental change. The research suggests that a new generation of realistic forest modelling, which is urgently needed and now within reach, will significantly improve an understanding of how forests work, how tree species respond to deforestation, and how forests impact climate regulation and environmental change.

The research points out that forest dynamics (how populations of trees interact with each other and the environment) remains the single most important outstanding component in fully understanding climate change. There trillions of trees on the planet, made up of more than 100,000 species, which contain as much carbon as is currently in the atmosphere and serve as home to two-thirds of the planet’s terrestrial biodiversity. However, while other climate change factors such as ocean dynamics are now well researched, the effects of changes to the world’s forests are still largely unknown.

The paper “Predictive Models of Forest Dynamics” by Purves and Princeton’s Stephen Pacala explores dynamic global vegetation models (DGVMs), which simulate the reaction of forests to past, present and future climate.

“DVGMs have shown that forests could be a crucial part of the way the Earth’s climate responds to man-made CO2 emissions, but insufficient understanding of forests, and insufficient data and computing power, have made their predictions highly uncertain,” Purves said. “This kind of uncertainty helps climate sceptics, who erroneously conclude that because the Earth is a complex but poorly understood system, we should not change our behaviour. However, we suggest that the convergence of recently developed mathematical models, improved data sources and new methods in computational data analysis could produce more realistic models. That would give us truly invaluable information to help manage the world’s forests and understand their impact on our climate.”

“Until now, one of the most important pieces of the climate change jigsaw has been missing,” Pacala said. “We argue that we can significantly further our understanding of forest dynamics if scientists work together to use new computational techniques and data sources — provided governments and others make more data available in useful forms. We feel that these discoveries could unlock the climate change mysteries of forests on a global scale in as little as five years.”

The second paper published in Science today, “Animal vs Wind Dispersal and the Robustness of Tree Species to Deforestation,” by Daniel Montoya from the Universidad de Alcalá in Madrid and Purves in Cambridge, with Miguel A. Rodríguez of the Universidad de Alcalá and Miguel A. Zavala of Centro de Investigación Forestal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA-CIFOR) in Madrid, examines what happens to individual tree species in the face of deforestation. Using data from nearly 90,000 survey plots in the Spanish peninsula, the paper found tree species that rely on wind to disperse seeds, rather than animals, are more vulnerable to deforestation.

Montoya said, “By applying various methods in computational data analysis to a large source of forest data, we have confirmed that, in Spain at least, plants with animal-dispersed seeds are less vulnerable to habitat loss, because animals provide trees with an intelligent dispersal mechanism, travelling and distributing seeds between areas of remaining forest. In contrast, a wind dispersal method is more susceptible to habitat loss, as seeds are more likely to fall in inhospitable environments. Using methods like this, conservationists can identify the species at most risk following deforestation, and use this knowledge to develop new strategies to mitigate the effects of widespread habitat loss and help to protect species diversity.”

The research also concludes that when no animal dispersers exist in the ecosystem, animal-dispersed tree species are the most vulnerable to deforestation. This means that protecting plant-animal interactions must also be a cornerstone of conservation policy, because the interactions not only create and maintain biodiversity, but also increase resistance to disturbances to the ecosystem.

Both papers underline the importance of forest dynamics in understanding and predicting climate change and biodiversity, highlighting the urgent need for additional study and resources. Purves said, “It is imperative that we create the tools and science to accurately understand the reaction of ecosystems to climate change and other forces — not just for plants and animals, but for our children and succeeding generations.”

This research is part of the recently established Computational Science Research at Microsoft Research Cambridge. This team of ecologists, biologists, neuroscientists, mathematicians and computer scientists is pioneering novel theoretical frameworks, computational tools and scientific methods to tackle the greatest scientific and societal challenges of this century, from climate change and declining biodiversity to understanding how living things work.

Forest management that favors single tree species and climate change are just two of the critical factors making forests throughout western North America more susceptible to infestation by bark beetles, according to an article published in the June 2008 BioScience. Bark beetle epidemics have become more extensive and frequent in recent years as winter temperatures have risen, and an eruption of mountain pine beetles is currently devastating lodgepole pines throughout the mountainous West.

The article, by Kenneth F. Raffa of the University of Wisconsin at Madison and colleagues at Colorado State University, the University of Idaho, and the US and Canadian Forest Services, stresses the complexity of the biological processes that determine when a bark beetle eruption will occur. When beetles bore through a tree’s bark, they release pheromones that summon other beetles to join the offensive. Trees counter attacks by exuding resin that can kill the invaders, but if too many beetles attack a weak tree, its defenses fail. The beetles then reproduce within its living tissues, with the help of colonizing fungi, and the tree is doomed. The condition and spacing of nearby trees and the local climate affect whether the beetle progeny released after a successful attack sustain an epidemic–which can kill a high proportion of the trees in an area and so alter the landscape for decades. Because many of the processes in an epidemic operate at different scales and turn on critical thresholds, prediction is a challenge. It is nonetheless clear that human activities can exacerbate bark beetle eruptions, which cause major economic losses and reduce forests’ ability to absorb carbon from the atmosphere.

Ecosystems are constantly exchanging materials through the movement of air in the atmosphere, the flow of water in rivers and the migration of animals across the landscape. People, however, have also established themselves as another major driver of connectivity among ecosystems. In the June 2008 Special Issue of Frontiers in Ecology and the Environment, titled “Continental-scale ecology in an increasingly connected world,” ecologists discuss how human influences interact with natural processes to influence connectivity at the continental scale. The authors conclude that networks of large-scale experiments are needed to predict long-term ecological change.

“We know that the world has always been connected via a common atmosphere and the movement of water,” says Debra Peters, an author in the issue and a scientist with the United States Department of Agriculture’s Agricultural Research Service (USDA-ARS). “The world is also becoming highly interconnected through the movement of people and the transport of goods locally to globally. Among ecologists, there is an increasing realization that these connections can have profound influences on the long-term dynamics of ecological systems.”

The transport of many types of materials, including gases, minerals and even organisms, can affect natural systems. This movement results in “greenlash,” which occurs when environmental changes localized to a small geographic area have far-reaching effects in other areas. For example, a drought in the 1930’s caused small-scale farmers to abandon their farms across the U.S. Midwest. The absence of crops intensified local soil erosion, leading to powerful dust storms. Large amounts of wind-swept dust traveled across the continent, causing the infamous Dust Bowl and affecting air quality, public health and patterns of human settlement throughout the country.

Because of increasing globalization, people often inadvertently introduce non-native plants, animals and diseases into new locations. Invasive species and pathogens, such as fire ants from South America and the SARS virus from China, can create large, expensive problems: the U.S. currently spends over $120 billion per year on measures to prevent and eradicate invasive species. Understanding ecosystem connectivity across a range of scales – from local to regional to continental – will help scientists predict where invasive species are likely to go next.

The authors agree that field ecology studies should focus on long-term sampling networks that encompass a range of geographical scales. Integrating data from existing and developing networks, such as the National Science Foundation’s Long Term Ecological Research network (LTER) and NSF’s National Ecological Observatory Network (NEON), will lead to a level of power for ecological comparison unparalleled by any one experiment.

“To draw conclusions about the consequences of increasing connectivity, we need to provide information about processes that span a vast scale of space and time,” says David Schimel, an author in the issue and the chief executive officer of the NEON project. “Our observations will characterize ecological processes from the genomic to the continental and document changes from seconds to decades.”

Additionally, the authors suggest that long-term studies should include data from social and behavioral science to allow incorporation of human movement patterns into their scientific models. Ecologists hope that understanding the patterns of connectivity within and among ecosystems will lead to more accurate predictions of future ecological change.

Short-term exposure to low levels of particulate air pollution may increase the risk of stroke or mini-stroke, according to findings that suggest current exposure standards could be insufficient to protect the public.”The vast majority of the public is exposed to ambient air pollution at the levels observed in this community or greater every day, suggesting a potentially large public health impact,” said Lynda Lisabeth, lead author and assistant professor in the University of Michigan School of Public Health.

However, Lisabeth stressed that the association requires further study in other areas with varying climates and alternative study designs. Stroke is the third leading cause of death in the United States.

The study examined particulate air pollution in a southeast Texas community where there is a large petroleum and petrochemical industry presence. Particulate matter is one type of air pollution, defined as tiny particles of solid or liquid that can cause numerous health problems when inhaled. These particles can be man-made or from natural sources.

In the study, researchers identified ischemic strokes and transient ischemic attacks (TIA), sometimes called mini strokes but that often lead to a stroke later. Ischemic attacks are caused by a blockage of blood flow to the brain by a blood clot.

The results showed borderline significant associations between same day and previous day fine particulate matter exposures and ischemic stroke/TIA risk. Similar associations were also seen with ozone, another type of pollution. Despite the fossil fuel industry in the area, fine particulate matter exposures were low relative to other regions of the country, probably because of the proximity to the coast and prevailing wind patterns.

Findings suggest that recent exposure to fine particulate matter may increase the risk of ischemic cerebrovascular events specifically. Some research has shown that particulate air pollution is associated with acute artery vasoconstriction and with increased thickening of the blood, which may enhance the potential for blood clots. However, this requires further study.

Researchers looked at data from the Brain Attack Surveillance in Corpus Christi Project, a population-based stroke surveillance project designed to capture all strokes in Nueces County, Texas. Ischemic stroke and TIA cases between 2001 and 2005 were identified using trained staff and later verified by neurologists. Daily historical air pollutant and meteorological data were obtained for the same time period from the Texas Commission on Environmental Quality’s Monitoring Operations database. Data on fine particulate matter and ozone were available from a centrally located monitor in Corpus Christi, Tex., located upwind of the local industrial facilities. The majority of stroke/TIA cases were also located upwind of local chemical plants and refineries.

Fishermen hold empirical knowledge that tuna aggregate under floating objects, such as lengths of old rope, pieces of wood, or even large marine mammals. There is still no full explanation for this aggregation behaviour, but the past 20 years have seen purse-seine fishery operators take advantage of the associated concentrations of fish. Fishermen cast off floating rafts equipped with buoys which act as FADs. An enormous purse-seine net, deployed in a wide arc on either side of the vessel, encircles the school of tuna that come to shelter under the FAD. The lower part of the net is tightened, enclosing the fish in a hemisphere large enough to entrap a mass of tuna.

A sudden growth in the size of tropical tuna catches taken from under these artificial drifting objects was observed for the early 1990s. This was true especially for juveniles. Between 1996 and 2005 the average annual catch taken on FADs reached 1 115 000 tonnes, nearly a third of the global figure for tuna, all species considered together. In Japan, the fish processing industry furthermore had long reported that the flesh from floating-object associated tuna was less plump than that of specimens caught from free schools. This prompted an IRD research team to investigate whether or not the practice of drifting FAD fishing could set up an ecological trap for the tropical tuna species.This trap concept is a notion from population biology used to describe situations in which the population falls following a sudden change in its environment, most often linked to human activity. An example is give by marine turtles which, after hatching on beaches, use the sparkle of moonlight on the sea surface to guide themselves back to the ocean. However, high light pollution levels on urbanized coastlines in certain regions disturbs their sense of direction. Young turtles therefore set off on a path that leads them to land, where they die from dehydration.

Over the past ten years, over 30% of world catches of skipjack (Katsuwonus pelamis), bigeye (Thunnus obesus) and yellowfin (Thunnus albacares) tuna, the three tropical tuna species which can be caught at drifting FADs, have been achieved using this fishing method. For the skipjack amounts taken under drifting FADs reached even as high as 72% of all catches. To check if the large-scale deployment of drifting FADs could present an ecological trap for these species, a range of biological (fish plumpness, growth rate, stomach fullness) and ecological (migration pattern and distance) indices were determined on yellowfin and skipjack captured under FADs in the Atlantic and Indian Oceans. Comparison was then made with data gathered from free-school caught individuals of these same species. A salient finding was that 74% of drifting FAD-associated skipjack had empty stomachs at the moment of capture compared with only 13% for those fished from free schools. Figures of the same order of magnitude were obtained for yellowfin, with proportions respectively reaching 49% caught on drifting FADs and 7% from free schools. The survey indicated that the tuna caught under the FADs fed less well than those fished from free schools. Moreover, the fact that for the same weight the FAD-associated specimens caught showed lower plumpness than the free-school ones could reflect a deficiency in energy-reserve accumulation in those that concentrated around the floating devices.

The research team also sought to find out if the large-scale deployment of drifting FADs could affect the migration patterns of these far-travelling fish species. Tagging surveys allowed comparison of the nature of migrations accomplished by fish moving with the drift of FADs with that of non-FAD-associated individuals. The migration directions and displacement rates in terms of daily distances travelled were indeed affected by the presence of artificial floating objects. Drifting FADs therefore appeared to act as super-stimuli, like strong magnets exerting a binding attraction that leads the tuna towards ecologically inappropriate waters with scarcer food supplies. This survey brought support for a body of reasonable assumptions regarding the tuna behaviour. However, it did not provide certain confirmation of drifting FADs’ negative impact on the entire life cycle of these tuna species and therefore of their possible role as a true ecological trap. Nevertheless, the biological effects observed indicated that it would be more reasonable to preclude deployment of drifting FADs near coasts where tuna juveniles aggregate. These young fish represent the future of the whole stock and such a restriction would be a way of avoiding their being led astray, away from the zones which are ecologically most favourable to them.

A mat of nanowires with the touch and feel of paper could be an important new tool in the cleanup of oil and other organic pollutants, MIT researchers and colleagues report in the May 30 online issue of Nature Nanotechnology.The scientists say they have created a membrane that can absorb up to 20 times its weight in oil, and can be recycled many times for future use. The oil itself can also be recovered. Some 200,000 tons of oil have already been spilled at sea since the start of the decade.

“What we found is that we can make ‘paper’ from an interwoven mesh of nanowires that is able to selectively absorb hydrophobic liquids-oil-like liquids-from water,” said Francesco Stellacci, an associate professor in the Department of Materials Science and Engineering and leader of the work.

In addition to its environmental applications, the nanowire paper could also impact filtering and the purification of water, said Jing Kong, an assistant professor of electrical engineering in the Department of Electrical Engineering and Computer Science and one of Stellacci’s colleagues on the work. She noted that it could also be inexpensive to produce because the nanowires of which it is composed can be fabricated in larger quantities than other nanomaterials.

Stellacci explained that there are other materials that can absorb oils from water, “but their selectivity is not as high as ours.” In other words, conventional materials still absorb some water, making them less efficient at capturing the contaminant.

The new material appears to be completely impervious to water. “Our material can be left in water a month or two, and when you take it out it’s still dry,” Stellacci said. “But at the same time, if that water contains some hydrophobic contaminants, they will get absorbed.”

Made of potassium manganese oxide, the nanowires are stable at high temperatures. As a result, oil within a loaded membrane can be removed by heating above the boiling point of oil. The oil evaporates, and can be condensed back into a liquid. The membrane-and oil-can be used again.

Two key properties make the system work. First, the nanowires form a spaghetti-like mat with many tiny pores that make for good capillarity, or the ability to absorb liquids. Second, a water-repelling coating keeps water from penetrating into the membrane. Oil, however, isn’t affected, and seeps into the membrane.

The membrane is created by the same general technique as its low-tech cousin, paper. “We make a suspension of nanowires, like a suspension of cellulose [the key component of paper], dry it on a non-sticking plate, and we get pretty much the same results,” Stellacci said.

In a commentary accompanying the Nature Nanotechnology paper, Joerg Lahann of the University of Michigan concluded: “Stellacci and co-workers have provided an example of a nanomaterial that has been rationally designed to address a major environmental challenge.”

In this week’s issue of Science, a team of researchers from the United States and Sweden report on a newly identified factor that controls the natural input of new nitrogen into boreal forest ecosystems. Nitrogen is the primary nutrient that dictates productivity (and thus carbon consumption) in boreal forests. In pristine boreal ecosystems, most new nitrogen enters the forest through cyanobacteria living on the shoots of feather mosses, which grows in dense cushions on the forest floor. These bacteria convert nitrogen from the atmosphere to a form that can be used by other living organisms, a process referred to as “nitrogen-fixation.” The researchers showed that this natural fertilization process appears to be partially controlled by trees and shrubs that sit above the feather mosses.

In the summer of 2006, the researchers placed small tubes, called resin lysimeters, in the moss layer to catch nitrogen deposited on the feather moss carpets from the above canopy and then monitored nitrogen fixation rates in the mosses. The studies revealed that when high levels of nitrogen were deposited on the moss cushion from above, a condition typical of young forests, nitrogen fixation was extremely low. In older, low-productivity forests, very little nitrogen was deposited on the moss cushion, resulting in extremely high nitrogen fixation rates.

Nitrogen fixation is an energy demanding process. Thus, when mosses are exposed to high concentrations of bioavailable nitrogen, the cyanobacteria will consume this resident nitrogen rather than expending energy on fixing new nitrogen. Thus the nitrogen content of canopy throughfall acts as a regulator of newly fixed nitrogen into these boreal forests. For this same reason, elevated nitrogen deposition from pollution likely reduces moss nitrogen fixation rates. The moss would initially buffer the forest against the effect of nitrogen added as pollution or fertilizer; however, chronic elevated nitrogen inputs would ultimately eliminate this natural source of forest fertility.

The feather moss-cyanobacterial association provides a unique model system in which to study nitrogen feedback mechanisms. The cyanobacteria reside on the leaves, thus the nitrogen status of the canopy throughfall directly influences nitrogen fixation in the feather mosses. This direct expression of a nutrient feedback mechanism could not be detected in other nitrogen fixing plant species, such as legumes, that house their nitrogen fixing bacteria below ground and where soils and decomposing litter intercept and modify the nitrogen from throughfall before it reaches the bacteria.

These findings are important from a global standpoint, because feather mosses (and associated cyanobacteria) are the primary source of biologically fixed nitrogen in the boreal forest biome. The dominating feathermoss Pleurozium schreberi is also found in arctic and temperate biomes and thus may be the widest distributed individual nitrogen-fixing plant species on Earth. Understanding feed back mechanisms among dominating organisms that regulate fundamental ecosystem processes are integral to our ability to predict long term outcomes of global carbon dynamics.