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Harvesting sugarcane in south Florida, ARS scientists at the Sugarcane Production Research Unit are identifying research to help sustain both agriculture and natural Everglades ecosystems.


Harvesting sugarcane in south Florida, ARS scientists at the Sugarcane Production Research Unit are identifying research to help sustain both agriculture and natural Everglades ecosystems.

This post is part of the Science Tuesday feature series on the USDA blog. Check back each week as we showcase stories and news from USDA’s rich science and research portfolio.

Most of us accept that some services—such as waste water treatment and emergency response, for example—have an economic value. As citizens, we decide to support these services for our safety, security and comfort. And yet there are many other functions going on every day, all around the world, that are not directly supported but still enable our planet to maintain favorable living conditions for all living creatures—functions like bees pollinating our crops, forests absorbing excess carbon dioxide, or dung beetles breaking down animal wastes.

These functions, known as ecosystem services, include all the jobs performed by the components of an ecosystem, coming from biotic components like plants and insects, to abiotic components, such as the soil and wind.  Ecosystem services include things like pollination (approximately one third of the human diet comes from insect pollinated plants), water filtration (wetlands protect water quality by trapping sediments and retaining pollutants such as heavy metals), energy (7 percent of US power comes from hydroelectric plants), and tourism (nature-based tourism or ecotourism is predicted to grow to 25 percent of the world travel market by 2012).  And these services, without most of us even knowing it, add substantially to our economy.  For example, the value of insect pollination has been estimated at up to $15 billion in the United States annually, and ecotourism has a worldwide value of approximately $473 billion per year.

As a growing world population slowly pushes ecosystem services to new limits, the issue that more and more scientists and policymakers are trying to confront is how to value ecosystem services.  Because we don’t directly support many of these services, we may undervalue them.  Yet ecosystem services are very valuable to agriculture, which is why USDA scientists and policy makers are increasingly working to understand ecosystem services and find ways to elevate our understanding of their importance and value them at the same time.

Many USDA agencies have active research programs in the area of ecosystem services. For example, ERS is investigating the economics of ecosystem services and design issues for ecosystem service markets, including the use of greenhouse gas offsets and interactions with conservation programs.  NIFA has several programs that address environmental markets, including a program on enhancing ecosystem services from agricultural lands and the National Integrated Water Quality Program, whose goal is to contribute to the improvement of the quality of our nation’s surface water and groundwater resources through research, education, and extension activities.  And ARS has a Water Availability & Watershed Management National Program which addresses the highest priorities for agricultural water management including erosion, sedimentation, and water quality protection, and improving watershed management and ecosystem services in agricultural landscapes.

Agriculture plays a major role in protecting ecosystem services, and in turn can reap great benefits from services that are functioning properly. Given that, it’s encouraging to know that USDA scientists and policy makers will continue to do their part to ensure that America’s ecosystems are able to provide the services we all need long into the future.

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Giraffes and other African hoofed animals are only slowly returning to the former grounds of the Mkwaja Ranch. (Credit: Judith Sitters / ETH Zurich)

ScienceDaily (June 30, 2010) — The Swiss wanted to rear cattle in Tanzania and in so doing completely disturbed the ecosystem: the example of the Mkwaja Ranch shows how dependant agriculture is on a functioning ecosystem. And what a serious effect its encroachment can have on a sensitive balance.

Giraffes and other African hoofed animals are only slowly returning to the former grounds of the Mkwaja Ranch (picture: Judith Sitters / ETH Zurich) (more pictures)

After the Second World War a practical experiment was carried out in Tanzania, which provided deep insights into the diversity of ecosystems. The Mkwaja Ranch was founded in the 1950s by the Anglo-Swiss sisal producer Amboni. Here, in the savannah of western Tanzania, the company wanted to rear cattle in order to be able to provide the workers on their sisal plantations with good meat. The ranch was built near the coast over an area of 400 square kilometres. Using native Zebu cows and Boran bulls from Kenya, Swiss farmers bred fast growing and robust high-performance cattle. In contrast to the European standard of breeding, the animals were initially reared in the African manner. They were allowed to graze during the day and spent the night in protective enclosures, so-called bomas or kraals.

Tsetse flies out of control

The experiment started successfully, the cattle thrived and the ranch management was satisfied. Then, however, the cattle started to be affected by diseases which were transmitted by ticks and tsetse flies. The farmers tried, unsuccessfully, to get the fly situation under control by using fly barriers and sterilised males, and for decades they concentrated on medical treatment and prophylaxis. While the ranch management were busily concentrating on fighting the diseases, they overlooked the beginning of a subtle and disastrous development: bushes were growing on the grassland.

The appearance of bushes became the biggest problem of this practical experiment. It was the reason why the experiment ultimately failed. The general economic and political conditions of Amboni also changed, sisal production was no longer profitable for them and as a result they gave up the ranch in 2000. The land was turned into a national park.

Even in the early 70s, the farm management had already realised that the situation was in danger of running out of control and got help from ETH Zurich. In 1973 Frank Kloetzli, a titular professor emeritus for plant sociology and botany, began to work out a scientific basis for a change of strategy by the management. He found out that the redistribution of nutrients, which was being caused by the large amounts of manure in the bomas, could be reduced by rotational grazing.

Kloetzli used goats to prevent the growth of bushes, a measure which was successful for a while. The wide range of problems caused by the interventions in the complex savannah ecosystem, however, eventually became too much for the farm management. "The cultivation of the ranch was becoming increasingly expensive," explains Peter Edwards, Professor of Plant Ecology at ETH "and so it had to be closed in the end." From 1998 onwards Edwards has continued research on the ranch. To date he has led three research projects to discover what influence cattle breeding has on the savannah ecosystem.

Chain-reaction of cattle breeding

In the first phase the plant ecologist and his team examined what effects cattle rearing had on the ecosystem of the ranch area. At its peak, there were some 15,000 cattle here. They displaced the local wildlife such as antelopes and giraffes, which used to shape the vegetation through their grazing. Without the grazing of native wildlife the original savannah with its open grassland and permeable tree population changed, with tall grassy vegetation arising in its place. And instead of trees, which were unable to stand the grazing pressure of the cows, bushes grew.

This finding was linked with another: the redistribution of nutrients in the ground due to the high amount of livestock made the animals more susceptible to diseases. In addition some invasive plant types took root, spreading quickly across the area which was rich in nutrients. It is not fully clear whether biodiversity suffered over the 50 years of cattle grazing, says Edwards. "We can say for sure that the quality of the biodiversity is worse and therefore that the ecosystem has been damaged. It is, however, virtually impossible to measure whether the overall biodiversity has worsened."

But the ecosystem itself has suffered severely. "Due to the loss of natural hoofed animals, the area cannot even be called a real savannah anymore" says the biologist. And the displaced wildlife is only slowly moving back to the area, as Edwards and his team were forced to recognise in a second research project. The transition from an area used for cattle-grazing to a natural ecosystem will therefore take a while.

Edward's latest research project, which he is carrying out together with the wildlife biologist Werner Suter from the Swiss Federal Research Institute for Forests, Snow and Agriculture (WSL), should now show what effect the returning wildlife is having on the ecosystem. It is still too early for specific results, says Edwards. A few conclusions can, however, already be drawn: "We observed very diverse feeding behaviour amongst the different hoofed animals." For example some, such as the bushbuck, a small antelope, feed very selectively and on a small area. "This produces a positive reaction, as on this area the vegetation is changing and the quality of nutrition for this species is therefore improving. The animals thereby create conditions in which they are able to live."

An ecosystem without animals

What findings can be deduced from this practical experiment in Tanzania for other ecosystems? According to Edwards, "We are getting a much better understanding of how the savannah system functions. Here we can see quite clearly, what an important role hoofed animals play." We can also see from this example that recreating an ecosystem is not easy. "The example of the Mkwaja Ranch also clearly shows that the ecosystem is completely different without animals," continues Edwards. Specific measures are probably going to be necessary to get the wildlife to return within a useful period.

The findings from Edward's research are very helpful, particularly for Africa, as poaching has severely reduced wildlife stocks in many savannah areas, and the relocation of wild animals is problematic. Edwards: "Bringing an ecosystem back to life without animals is a great challenge."

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The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by ETH Zurich.

Journal Reference:

  1. Gross M, Hoffmann-Riem H, Krohn W. Practical experiments. Ecological structuring processes in the knowledge-based society. Science Studies, 2005. 234 p

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Público 20100220 Helena Geraldes


O aliado da Câmara do Seixal para combater a praga da processionária-do-pinheiro tem penas coloridas, canta e mede entre 11 e 16 centímetros. Mas é eficaz no seu papel de predador natural. A população foi desafiada a instalar ninhos de chapim e a partir de hoje já serão 123.

No dia em que terminaram as inscrições para o projecto "O Chapim vem ao Seixal", a 31 de Janeiro, a autarquia tinha 34 pessoas que ofereciam as suas casas para a instalação de ninhos para as cinco espécies de chapim que vivem no concelho. "Infelizmente, nem todos os que se inscreveram moram nas zonas incluídas no projecto, ou seja, áreas de pinhal", lamentou Jorge Didelet, director do Departamento de Ambiente da Câmara do Seixal. Por isso, hoje serão instaladas apenas 15 caixas-ninho nas zonas da Verdizela, Foros de Amora e Belverde. "Contamos com um grande apoio da população", comentou ao PÚBLICO, referindo-se a um projecto que começou em 2008. Nesse ano foram distribuídos 62 ninhos, dos quais resultaram 173 ovos e 100 crias. No ano seguinte foram instalados 46 ninhos e este ano, outros 15.

A operação decorre numa altura em que a praga se torna mais visível, entre Janeiro e Março. Longas filas de lagartas (Thaumetopoea pityocampa Schiff) descem dos seus ninhos nos pinheiros em direcção ao solo, em busca de locais para se enterrarem. O fenómeno não é inócuo. Os pêlos urticantes destas lagartas causam alergias na pele, nos olhos e no aparelho respiratório, colocando problemas de saúde pública.

A estratégia de combate da autarquia, que começou apenas com tratamentos químicos, passou, em 2006, a contar com a ajuda dos chapins, predadores naturais daquela lagarta e que se alimentam de sementes e insectos. Segundo a câmara, um chapim come até um terço do seu peso, todos os dias. Numa primeira fase, os ninhos eram instalados nas escolas onde o problema era mais sentido. Agora, toda a população está envolvida. "Além de instalarmos os ninhos, damos orientações às pessoas sobre como acompanhar os ninhos, como devem ser observadas as aves e quais os cuidados de limpeza a ter", explicou o responsável. Em média, o chapim vive cerca de quatro anos e cada casal coloca, por ano, entre cinco a seis ovos.

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ScienceDaily (Dec. 21, 2009) — Human activity is increasing the supply of nutrients, such as nitrogen and phosphorus, to stream systems all over the world. The conventional wisdom -- bolstered by earlier research -- has held that these additional nutrients cause an increase in production all along the food chain, from the tiniest organisms up to the largest predators. A long-term, ecosystem-scale study by a team of University of Georgia researchers, however, has thrown this assumption into question.

The researchers -- a team from the UGA Odum School of Ecology and department of entomology in the College of Agricultural and Environmental Sciences -- found, unexpectedly, that while nutrient enrichment did indeed cause a steady increase in the production of organisms lower on the food chain, organisms at the top of the food chain did not benefit.

Their study, published in Proceedings of the National Academy of Sciences, was funded by the National Science Foundation. It documents the effects of long-term nutrient enrichment of a headwater stream in a forested area at the Coweeta Hydrologic Laboratory in North Carolina. For the first two years of the study, the results were as expected: the production of both prey (the organisms low on the food chain) and predators (in this case salamanders and macroinvertebrates) increased. But with continued addition of nutrients, things began to change. While the prey continued to increase at the same rate, the production of predators leveled off, signifying a 'decoupling' of the typical relationship between predators and prey.

Maintaining patterns of energy flow between predators and prey is a critical aspect of healthy ecosystems. "What we found was a dead end in the food chain," said Amy Rosemond, assistant professor at the Odum School, and one of the lead researchers. "This is the first time we've seen this kind of trophic decoupling, or break in the food chain, between the levels of prey and predator on this scale. This kind of disruption of the food web wasn't on anyone's radar screen before now. "

In this instance, Rosemond explained, the break was driven by the traits of the various prey species that inhabit the stream system. Some of these species were better able to take advantage of the extra nutrition than were others. After the first two years, the nutrient enrichment began to favor the growth of large-bodied prey, such as the caddisfly, Pycnopsyche spp., over smaller organisms. These large-bodied prey were simply too big for the stream's predators to consume; hence, they were unable to capitalize on the increase in available food.

John Davis, who conducted the research as part of his Ph. D. dissertation, said that the work has global implications. "Nutrient enrichment is a global threat to the health of freshwater ecosystems," he explained. "However, our understanding of its effects is limited. Our experimental results varied substantially from the few other large-scale experiments, which suggests that ecosystem-level responses to nutrient enrichment are largely context-dependent. This is important because humans are increasing nutrient loading rates to a diversity of ecosystems, but our understanding of their effects is based on only a small number of ecosystem types. "

Rosemond said that their results point to the need for more research, especially large-scale, long-term studies in a variety of ecosystems. Davis agrees. "It took over four years for nutrient enrichment to decouple predator and prey production within these headwater streams," he said. "But most ecological experiments are limited to time scales of weeks to months. "

And the need to understand the effects of nutrient enrichment continues to grow more important. According the Environmental Protection Agency, the health of 47 percent of lakes and 45 percent of streams in the U. S. is impaired, with excessive nutrients a significant source of that impairment. Nutrient inputs to lakes and streams are likely to continue to increase globally from fertilized agricultural and suburban lands and from human and animal wastes that enter aquatic systems from treated sewage, septic tanks, or run-off from land. Furthermore, headwater streams, like the study stream in Coweeta, may account for as much as 73% of all stream miles. These headwater streams are the 'feeders' of larger rivers, so their response to nutrient enrichment likely affects downstream systems as well. But long-term effects of nutrients have not been previously tested in these systems.

"Without more accurately assessing the long-term effects of nutrients on a diversity of ecosystem types," Davis concluded, "we won't be able to adequately predict how global ecosystems are going to respond to chronic nutrient enrichment. "


Journal Reference:

  1. Davis et al. Long-term nutrient enrichment decouples predator and prey production. Proceedings of the National Academy of Sciences, 2009; DOI: 10.1073/pnas.0908497107

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