Model shows ‘waves of forest degradation’


An international team of researchers has developed a model that suggests degradation of tropical forests occurs in a series of “waves”, reports the BBC News website’s Mark Kinver.

High-value trees were felled in the first “wave”, followed by a wave that removed mid-value timber before the remaining wood was felled for charcoal.

The team hopes the model will help manage forests as vital carbon sinks and limit the loss of biodiversity.

The findings appear in the Proceedings of the National Academy of Sciences.

The researchers said an economic theory was used to provide a general model to predict patterns of tree loss.

This translates to a prediction that waves of forest degradation will emanate from major demand centres and expand into nearby forested areas, targeting resources in sequence, starting with those of highest value,” they wrote in their PNAS paper.

“Such a sequence of demand, linked to resource utilisation, has been demonstrated for unmanaged fisheries… but has not been shown for the exploitation of differently valued tropical forest products.”

The team used data collected in the area surrounding Tanzania’s largest city, Dar es Salaam, to see how far the degradation “waves” had travelled between 1991 and 2005.

“The first wave that emanates is high-value timber, and that is mostly used for export,” explained co-author Antje Ahrends, an ecologist at the Royal Botanical Garden, Edinburgh.

“There has been a massive demand for this in China, and this is where most of the timber ends up.”

Dr Ahrends said the first wave moved out from Dar es Salaam rapidly, averaging about nine kilometres each year, because the “timber companies had lorries and loads of people working for them”.

“For the firms, it is only worthwhile to stay in a forest when timber can be accessed relatively easily,” she told BBC News.

“So once it becomes not so easy to get hold of the rest, the companies generally move on.”

The first wave had already moved outside of the team’s study area, and Dr Ahrends estimated that it was already more than 200km from Dar es Salaam.

The second wave saw trees being felled for medium-valued timber, which was generally used in the city for construction and furniture.

“This is expanding very rapidly, in line with urban migration,” she explained. “The town has an average growth rate of about 7% each year, so there is – again – a rapidly growing demand for this material.”

The timber is harvested by local companies, again with lorries, allowing large volumes to be collected in a relatively short space of time. This resulted in this degradation wave to also cover about nine kilometres each year.

The third and final wave involved local people collecting wood to make charcoal for cooking.

“It’s the most destructive of all of the waves because charcoal burners would collect everything,” observed Dr Ahrends, who was based at the York Institute for Tropical Ecosystem Dynamics when she carried out this research.

“It is only worthwhile moving on once there are no sizeable trees left in the forest.”

As a result, the charcoal wave had moved relatively slowly – from 20km outside Dar es Salaam in 1991 to 50km away in 2005.

“It is the most difficult of the waves to tackle because it is very poor people who burn charcoal and their livelihoods depend upon it.”

“Targeting that wave would mean trying to provide alternative resources for cooking, and alternative incomes for people who burn charcoal.

Species loss

The team also developed their model to gauge what impact forest degradation had on “public good” services, such as carbon storage and biodiversity.

They did this by recording what species of trees were in a particular area of the study, and what size the individual trees were.

“This later enabled us to calculate species richness and also the amount of carbon those trees were storing,” Dr Ahrends said.

“We found that there was a very strong linear impacts; for example, tree species richness dropped to only 14 species-per-sample-unit close to Dar es Salaam, whereas it is more than 40 species in areas 200km away.”

Dr Ahrends suggested that the model could be used to understand the impact of forest degradation in other sub-Sarahan nations in Africa.

“This is because conditions are very similar: high levels of corruption, weak law enforcement and very rapid rates of urbanisation.”

She added that the team’s model could help policymakers who were looking at ways to limit deforestation rates.

“What is really important is to understand the pattern of degradation and the way it spreads,” she suggested.

“While we have a good understanding of deforestation – which is the complete clearance of a forest – it is much more difficult to measure degradation.

“So if you have this simple model, then you have a basic understanding of how degradation might spread… which may help you develop some prediction of where it might spread from and how far it might spread.”

Source: BBC News website

Date: 03/08/2010

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Climate ‘adds fuel to Asian wildfire emissions’


In the last decade, Asian farmers have cleared tens of thousands of square miles of forests to accommodate the world’s growing demand for palm oil, an increasingly popular food ingredient, reports Science Daily.

Ancient peatlands have been drained and lush tropical forests have been cut down.

As a result, the landscape of equatorial Asia now lies vulnerable to fires, which are growing more frequent and having a serious impact on the air as well as the land.

A team of NASA-sponsored researchers have used satellites to make the first series of estimates of carbon dioxide (CO2) emitted from these fires — both wildfires and fires started by people — in Malaysia, Indonesia, Borneo, and Papua New Guinea.

They are now working to understand how climate influences the spread and intensity of the fires.

Using data from a carbon-detecting NASA satellite and computer models, the researchers found that seasonal fires from 2000 to 2006 doubled the amount of carbon dioxide (CO2) released from the Earth to the atmosphere above the region.

The scientists also observed through satellite remote sensing that fires in regional peatlands and forests burned longer and emitted ten times more carbon when rainfall declined by one third the normal amount.

The results were presented in December 2008 in Proceedings of the National Academy of Sciences.

Tropical Asian fires first grabbed the attention of government officials, media, and conservationists in 1997, when fires set to clear land for palm oil and rice plantations burned out of control.

The fires turned wild and spread to dry, flammable peatlands during one of the region’s driest seasons on record. By the time the flames subsided in early 1998, emissions from the fires had reached 40 percent of the global carbon emissions for the period.

“In this region, decision makers are facing a dichotomy of demands, as expanding commercial crop production is competing with efforts to ease the environmental impact of fires,” said co-author Jim Collatz, an Earth scientist at NASA’s Goddard Space Flight Center.

“The science is telling us that we need strategies to reduce the occurrence of deforestation fires and peatlands wildfires. Without some new strategies, emissions from the region could rise substantially in a drier, warmer future.”

Since the 1997 event, the region has been hit by two major dry spells and a steady upswing in fires, threatening biodiversity and air quality and contributing to the buildup of CO2 in the atmosphere.

As more CO2 is emitted, the global atmosphere traps more heat near Earth’s surface, leading to more drying and more fires.

Until recently, scientists knew little about what drives changes in how fires spread and how long they burn. Dr Collatz, along with lead author Guido van der Werf of Vrije University, Amsterdam, and other colleagues sought to estimate the emissions since the devastating 1997-98 fires and to analyse the interplay between the fires and drought.

They used the carbon monoxide detecting Measurements of Pollution in the Troposphere (MOPITT) instrument on NASA’s Terra satellite — as well as 1997-2006 fire data and research computer models — to screen for and differentiate between carbon emissions from deforestation versus general emissions.

Carbon monoxide is a good indicator of the occurrence of fire, and the amounts of carbon monoxide in fire emissions are related to the amount of carbon dioxide.

They also compared the emissions from different types of plant life (peat land verses typical forest) by examining changes in land cover and land use as viewed by Terra’s Moderate Resolution Imaging Spectradiometer (MODIS) and by Landsat 7.

Collatz explained that two climate phenomena drive regional drought.

El Nino’s warm waters in the Eastern Pacific change weather patterns around the world every few years and cause cooler water temperatures in the western Pacific near equatorial Asia that suppress the convection necessary for rainfall.

Previously, scientists have used measurements from NASA’s Tropical Rainfall Measurement Mission satellite to correlate rainfall with carbon losses and burned land data, finding that wildfire emissions rose during dry El Nino seasons.

The Indian Ocean dipole phenomenon affects climate in the Indian Ocean region with oscillating ocean temperatures characterized by warmer waters merging with colder waters to inhibit rainfall over Indonesia, Borneo, and their neighbors.

“This link between drought and emissions should be of concern to all of us,” said co-author Ruth DeFries, an ecologist at Columbia University in New York.

“If drought becomes more frequent with climate change, we can expect more fires.”

Collatz, DeFries, and their colleagues found that between 2000 and 2006, the average carbon dioxide emissions from equatorial Asia accounted for about 2 percent of global fossil fuel emissions and 3 percent of the global increase in atmospheric CO2.

But during moderate El Nino years in 2002 and 2006, when dry season rainfall was half of normal, fire emissions rose by a factor of 10. During the severe El Nino of 1997-1998, fire emissions from this region comprised 15% of global fossil fuel emissions and 31% of the global atmospheric increase over that period.

“This study not only updates our measurements of carbon losses from these fires, but also highlights an increasingly important factor driving change in equatorial Asia,” explained DeFries.

“In this part of Asia, human-ignited forest and peat fires are emitting excessive carbon into the atmosphere. In climate-sensitive areas like Borneo, human response to drought is a new dynamic affecting feedbacks between climate and the carbon cycle.”

In addition to climate influences, human activities contribute to the growing fire emissions.

Palm oil is increasingly grown for use as a cooking oil and biofuel, while also replacing trans fats in processed foods.

It has become the most widely produced edible oil in the world, and production has swelled in recent years to surpass that of soybean oil.

More than 30 million tonnes of palm oil are produced in Malaysia and Indonesia alone, and the two countries now supply more than 85% of global demand.

The environmental effects of such growth have been significant. Land has to be cleared to grow the crop, and the preferred method is fire.

The clearing often occurs in drained peatlands that are otherwise swampy forests where the remains of past plant life have been submerged for centuries in as much as 60 feet of water.

Peat material in Borneo, for example, stores the equivalent of about nine years worth of global fossil fuel emissions.

“Indonesia has become the third largest greenhouse gas emitter after the United States and China, as a result primarily to these fire emissions,” Collatz said.

“With an extended dry season, the peat surface dries out, catches fire, and the lack of rainfall can keep the fires going for months.”

Besides emitting carbon, the agricultural fires and related wildfires also ravage delicate ecosystems in conservation hotspots like the western Pacific island of Borneo, home to more than 15,000 species of plants, 240 species of trees, and an abundance of endangered animals.

Smoke and other fire emissions also regularly taint regional air quality to such a degree that officials have to close schools and airports out of concern for public health and safety.

Peat fires also aggravate air pollution problems in this region because they release four times more carbon monoxide than forest fires.

In 1997, air pollution from the fires cost the region an estimated $4.5 billion in tourism and business.

Source: Science Daily

Date: 10/05/2009

Tree-killing hurricanes ‘could contribute to global warming’


A first-of-its kind, long-term study of hurricane impact on US trees shows that hurricane damage can diminish a forest’s ability to absorb carbon dioxide from the atmosphere, Science Daily reports.

Tulane University researchers examined the impact of tropical cyclones on US forests between 1851 to 2000 and found that changes in hurricane frequency might contribute to global warming.

The results are published in the Proceedings of the National Academy of Sciences.

Trees absorb carbon dioxide as they grow, and release it when they die – either from old age or from trauma, such as hurricanes.

The annual amount of carbon dioxide a forest removes from the atmosphere is determined by the ratio of tree growth to tree mortality each year.

When trees are destroyed en masse by hurricanes, not only will there be fewer trees in the forest to absorb greenhouse gases, but forests could eventually become emitters of carbon dioxide, warming the climate.

Other studies, notes Tulane ecologist Jeff Chambers, indicate that hurricanes could intensify with a warming climate.

“If landfalling hurricanes become more intense or more frequent in the future, tree mortality and damage exceeding 50 million tonnes of tree biomass per year would result in a net carbon loss from US forest ecosystems,” says Dr Chambers.

The study, which was led by Tulane postdoctoral research associate Hongcheng Zeng, establishes an important baseline to evaluate changes in the frequency and intensity of future landfalling hurricanes.

Using field measurements, satellite image analyses, and empirical models to evaluate forest and carbon cycle impacts, the researchers established that an average of 97 million trees have been affected each year for the past 150 years over the entire United States, resulting in a 53-million ton annual biomass loss and an average carbon release of 25 million tons.

Forest impacts were primarily located in Gulf Coast areas, particularly southern Texas and Louisiana and south Florida, while significant impacts also occurred in eastern North Carolina.

Chambers compares the data from this study to a 2007 study that showed that a single storm – Hurricane Katrina – destroyed nearly 320 million trees with a total biomass loss equivalent to 50–140% of the net annual US carbon sink in forest trees.

“The bottom line,” observes Dr Chambers, “is that any sustained increase in hurricane tree biomass loss above 50 million tons would potentially undermine our efforts to reduce human fossil fuel carbon emissions.”

Study contributors include Tulane lab researchers Robinson Negrón-Juárez and David Baker; George Hurtt of the Institute for the Study of Earth, Oceans, and Space at the University of New Hampshire; and Mark Powell at the Hurricane Research Division, National Oceanic and Atmospheric Administration.

Source: Science Daily

Date: 10/05/2009

Amazon rainfall projections ‘underestimated’


Amazonian forests may be less vulnerable to dying off from global warming than feared because many projections underestimate rainfall, Reuters reports.

A study by UK researchers suggested that Brazil and other nations in the region would also have to act to help avert any irreversible drying of the eastern Amazon, the region most at risk from climate change, deforestation and fires.

“The rainfall regime in eastern Amazonia is likely to shift over the 21st Century in a direction that favours more seasonal forests rather than savannah,” the team write in the journal Proceedings of the National Academy of Sciences.

Seasonal forests have wet and dry seasons rather than the current rainforest, which is permanently drenched.

It is argued that this shift in precipitation patterns could result in the emergence of new species of trees, other plants and animals.

The findings challenge past projections that the Amazon forest could die and be replaced by savannah.

The Intergovernmental Panel on Climate Change reported in 2007: “By mid-century, increases in temperature and associated decreases in soil water are projected to lead to gradual replacement of tropical forest by savannah in eastern Amazonia.”

The new study said that almost all of 19 global climate models underestimated rainfall in the world’s biggest tropical forest.

Lowland forests in the Amazon have annual average rainfall of 2,400 mm (94 inches), it said.

Projected cuts in rainfall meant the region would still be wet enough to sustain a forest.

The experts also examined field studies of how the Amazon might react to drying.

It said that seasonal forests would be more resilient to the occasional drought but more vulnerable to fires than the current rainforest.

“The fundamental way to minimise the risk of Amazon dieback is to control greenhouse gas emissions globally, particularly from fossil fuel combustion in the developed world and Asia,” said Yadvinder Malhi, the lead author from Oxford University.

But he said that governments led by Brazil also needed to improve their forest management policies.

Global warming is “accompanied by an unprecedented intensity of direct pressure on the tropical forests through logging, deforestation, fragmentation, and fire use,” the scientists wrote.

And fires, including those touched off by lightning, were more likely to cause wide damage to forests already fragmented by roads or by farmers clearing land to plant crops, such as soya beans.

Source: Reuters

Date: 09/02/2009

Tropical farms ‘aid biodiversity’


A study has shown that certain farming methods can help sustain the biodiversity of tropical forests, reports BBC News’ environment reporter Mark Kinver.

Researchers found that an areca nut plantation in south-west India supported 90% of the bird species found in surrounding native forests.

The low-impact agriculture system has been used for more than 2,000 years and should be considered as a new option for conservation efforts, they added.

The findings appear in the Proceedings of the National Academy of Sciences.

The team of scientists from the US and India chose the site on the coastal fringes of the Western Ghat mountain range because it met a number of attributes the study required:

  • a long history of continuous agricultural production
  • intense human pressure
  • extensive natural areas still remaining

The landscape consisted of a mixture of intact forest, “production forest” (where non-timber products, such as leaves, were allowed to be removed) and areas of cash crops, primarily areca nut palms (Areca catechu).

“We found a total of 51 forest (bird) species in this study system,” the researchers wrote.

“These species were broadly distributed across the landscape, with 46 (90%) found outside of the intact forest.

“Within areca nut plantations, we recorded threatened forest species, such as the great hornbill (Buceros bicornis) and the Malabar grey hornbill (Ocyceros griseus).”

The team said the combination of the height of the areca nut palms (Areca catechu) and the plantations’ close proximity to the intact forest created the necessary ecological conditions to support forest bird species.

They added that data showed the distribution of species in the area had been relatively stable for more than 2,000 years, before the first farmers cultivated the area.

As well as having a high ecological value, the plantations were also economically productive.

The areca nut is consumed by about 10% of the world’s population, predominantly Asian communities.

The shade provided by the palms’ canopy also created the conditions that allowed farmers to grow other high-value crops, such as pepper, vanilla and bananas.

Rather than expanding the plantations, the farmers relied upon the leaf litter from the surrounding production forests to produce mulch for their crops, rather than using costly fertilisers.

The researchers also said alternative crops that could be grown in the wet lowlands, such as rice, yielded lower returns both economically and ecologically.

Lead author Jai Ranganathan, from the US National Center for Ecological Analysis and Synthesis (NCEAS), said the findings provided another option for conservationists to consider.

“It identifies another tool that can be used by conservationists,” he told BBC News.

“If it is not possible to make places completely protected areas then they can look at whether a system like this will help support the rich biodiversity.”

Dr Ranganathan said that he intended to look for further examples of established agriculture and cultivation practises in the region that provided habitats that supported a high level of biodiversity.

Source: BBC News website

Date: 04/11/2008

Why leaves fall from trees


Us researchers have published a paper in the Proceedings of the National Academy of Sciences (PNAS) in which they explain the sequence of events that cause plants to shed their leaves.

Writing in the UK’s Telegraph newspaper, science editor Roger Highfield explained that trees use an elaborate cellular mechanism to part company from their leaves, which act as “solar cells” in the summer but become superfluous in the darker winter months.

Reporting the researchers’ findings, he said that at the base of each leaf is a special layer called the abscission zone.

When the time comes in autumn to shed a leaf, cells in this layer begin to swell, slowing the transport of nutrients between the tree and leaf.

Once the abscission zone has been blocked, a tear line forms and moves downwards, until eventually the leaf is blown away or falls off. A protective layer seals the wound, preventing water evaporating and bugs getting in.

The discovery into how trees take on their winter aspect follows a study explaining the bright colours of autumn foliage.

Source: UK Telegraph newspaper

Date: 22/09/2008

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