China timber sector looks at tougher EU/US import rules


The China Timber and Wood Products Circulation Association (CTWPCA) is seeking to establish a body to help importers navigate new environmental regulations in the US and EU that restrict trade in illegally logged timber, reports the International Tropical Timber Organization (ITTO).

In a recent market report, ITTO said that Chinese importers fear failing to meet the new regulations that govern the sourcing of timber products.

The US’s Lacey Act and the EU’s FLEGT ruling put the burden of responsibility on importing companies, holding them to the environmental laws of producing countries.

Companies found to be sourcing illegally logged timber could be subject to fines or worse.

A company accused of using illicit rosewood from Madagascar, was the first company to be charged and investigated under the Lacey Act.

The legislation was amended in 2008 to include “anyone who imported, exported, transported, sold, received, acquired or purchased the wood products made from that illegal timber, who knew or should have known that the wood was illegal.” The firm’s case is pending.

According to ITTO, CTWPCA believes traders need “guidance and support” on the new international requirements.

The body would also set up a “responsible procurement system” for timber imports, seek to address corruption in the timber import and trade sector, and aim to help Chinese timber traders meet international standards.

China already has guidelines governing Chinese companies operating forest concessions overseas.

These compel companies to abide by local environmental laws and take measures to reduce pollution. However, some observers suggest that there is no indication that these mandatory rules are being enforced.

Source: Mongabay.com

Date: 02/09/2010

US wolf re-introduction still leaves aspens quaking


The re-introduction of wolves in a US National Park in the mid-1990s is not helping quaking aspens (Populus tremuloides) to become re-established, as many researchers hoped.

In a study published in the journal Ecology showed that the population of wolves in Yellowstone Park was not deterring elks from eating young trees and saplings.

It was assumed that the presence of wolves would create a “landscape of fear”, resulting in no-go areas for elks.

Researchers writing in the Ecological Society of America’s (ESA) journal said that the aspens were not regenerating well in the park as a result of the elk eating the young trees.

However, they added that the conventional wisdom suggested that as the wolves were predators of the elk, it was thought that the elk would eventually learn to avoid high-risk areas in which the wolves were found.

This would then allow plants in those areas – such as aspen – to grow big enough without being eaten and killed by the elk. And in the long-term, the thinking went, the habitat would be restored.

In this latest study, lead author Matthew Kauffman – a US Geological Survey scientist – suggested the findings showed that claims of an ecosystem-wide recovery of aspen were premature.

“This study not only confirms that elk are responsible for the decline of aspen in Yellowstone beginning in the 1890s, but also that none of the aspen groves studied after wolf restoration appear to be regenerating, even in areas risky to elk,” Dr Kauffman explained.

Because the “landscape of fear” idea did not appear to be benefiting aspen, the team concluded that if the Northern Range elk population did not continue to decline (their numbers are 40% of what they were before wolves), many of Yellowstone’s aspen stands were unlikely to recover.

“A landscape-level aspen recovery is likely only to occur if wolves, in combination with other predators and climate factors, further reduce the elk population,” observed Dr Kauffman.

The paper, Are wolves saving Yellowstone’s aspen? A landscape-level test of a behaviorally mediated trophic cascade, has been published online in Ecology. The authors of the paper are: Matthew Kauffman (USGS), Jedediah Brodie (University of Montana) and Erik Jules (Humboldt State University).

Source: ESA press release

Date: 01/09/2010

US Forest Services announces plan to save at risk forests


US Forest Service chief Gail Kimbell announced $50 million in grants to permanently protect 24 working forests across 21 States, as part of the  Forest Legacy Program, a USDA press release said.

The programme is designed to permanently protects important private forestland threatened by conversion.

“The Forest Legacy Program conserves open space, which allows us to respond to climate change, improves water quality and flows and connects children to nature,” said Agriculture Secretary Tom Vilsack.

“The strength of the Forest Legacy Program is the co-operation between States, partners and private landowners, all working together to protect environmentally and economically important forests that are threatened by conversion.”

Examples of 2009 projects include: forest essential for wildlife and recreation in Maine; pine ecosystem critical for threatened and endangered species in Arkansas and working forests that support rural jobs in Oregon.

The Forest Legacy Program promotes voluntary land conservation by operating on the principle of “willing buyer, willing seller”.

Private forest landowners are facing increasing real estate prices, property taxes and development pressure, which result in conversion of forests to other land uses.

The Forest Legacy Program focuses on conserving working forests – those that provide clean water, forest products, fish and wildlife habitat and recreational opportunities.

Most Forest Legacy Program projects are conserved through conservation easements, allowing landowners to keep their forestlands while protecting them from future development.

Source: USDA press release

Date: 18/05/2009

Top five invasive threats to US southern forests


Apologies that this post refers to information issued in a press release by the US Forest Service back in January, but it contains interesting data and links that could be of use to people – Take Cover team.

US Forest Service Southern Research Station (SRS) ecologist Jim Miller, considered to be one of the foremost authorities on non-native plants in the  southern US, has identified the five invasive plant species he believes pose the biggest threats to southern forest ecosystems in 2009.

“Cogongrass, tallowtree, and Japanese climbing fern are among the fastest moving and most destructive non-native plant species facing many southern landowners this year,” Dr Miller warned.

“Rounding out the top five invasive species that I’m very concerned about would be tree-of-heaven and non-native privets.

“While our forests are besieged by numerous invasive plants, these and other non-native species present serious financial and ecological threats to the South and its forests.”

Non-native species often out-compete native forest plants and may degrade forest productivity, wildlife habitat, recreational values, and water quality.

Invasive species also greatly increase expenses as public and private land managers work to combat their spread and deal with their effects (such as increased wildfire risk and severity).

Non-native plants can be introduced and spread by wildlife or through other natural means.

Humans also spread invasive species by planting them in their gardens and yards and as a result of seeds hitchhiking on clothes.

Additionally, tractors and mowers used in multiple locations without being cleaned often spread the plants.

In an effort to inform forest managers, landowners, and others about where the most threatening invasive plants are in the South, Dr Miller collaborated with SRS Forest Inventory and Analysis (FIA) scientists to develop maps showing the spread, county-by-county, across the south-east of more than 30 of the most serious non-native plant species.

The invasive plant data were collected on FIA plots throughout the southern US in co-operation with state forestry agencies.

In partnership with the University of Georgia’s Center for Invasive Species Science and Ecosystem Health, SRS researchers recently posted the maps and occupation levels online.

Dr Miller hopes government agencies, forest managers, natural resource professionals, landowners, students, and others will use the information to help combat the spread of non-native plant species in southern forest and grassland ecosystems.

Source: US Forest Service press release

Date: 12/01/2009

US shade trees cut bills and emissions


Shade trees on the west and south sides of a house in California can reduce a homeowners’ energy bills by about $25, a study has concluded.

The survey, involving 460 homes in the Sacramento area, is described as the “first large-scale study to use utility billing data to show that trees can reduce energy consumption”.

“Everyone knows that shade trees cool a house,” said co-author Geoffrey Donovan. “No one is going to get a Nobel Prize for that conclusion.

“But this study gets at the details,” he added. “Where should a tree be placed to get the most benefits? And how exactly do shade trees impact our carbon footprint?”

Dr Donovan is a research forester with the Forest Service’s Pacific Northwest (PNW) research station, compiled the findings with economist David Butry of the National Institute of Standards and Technology.

Some of the study’s key findings are:

  • Placement of a tree is the key to energy savings. Shade trees do affect summertime electricity use, but the amount of the savings depends on the location of the tree.
  • Trees planted within 40 feet of the south side or within 60 feet of the west side of the house will generate about the same amount of energy savings. This is because of the way shadows fall at different times of the day.
  • Tree cover on the east side of a house has no effect on electricity use.
  • A tree planted on the west side of a house can reduce net carbon emissions from summertime electricity use by 30%.

The report, The Value of Shade: Estimating the Effect of Urban Trees on Summertime Electricity Use, has been submitted for publication to the journal Energy and Buildings.

The researchers said they chose to do their study on homes in Sacramento because of the city’s hot summers and the fact that most people use air conditioners.

The Sacramento Municipal Utility District, in partnership Sacramento Tree Foundation, operates an active tree planting programme, in which residents are eligible for up to 10 free trees each year.

Source: press release

Date: 05/01/2009

Pine beetles ‘affecting Rockies air quality and climate’


When pine bark beetles kill trees, scientists believe they may also alter local weather patterns and air quality, reports the Environmental News Service (ENS).

For the next four years, researchers will study forests from southern Wyoming to northern New Mexico to determine the precise relationship between the beetles, the trees they kill and the atmosphere.

A new international field project, led by scientists at the National Center for Atmospheric Research (NCAR) in Boulder, is exploring how trees killed by the beetles influence rainfall, temperatures, smog and other aspects of the atmosphere.

“Forests help control the atmosphere, and there’s a big difference between the impacts of a living forest and a dead forest,” says NCAR scientist Alex Guenther, a principal investigator on the project. “With a dead forest, we may get different rainfall patterns, for example.”

Preliminary computer modeling suggests that beetle kill can lead to temporary temperature increases of between two and four degrees Fahrenheit. This is partly because of a lack of foliage to reflect the Sun’s heat back into space.

Beetle kill stimulates trees to release more particles and chemicals into the atmosphere as they try to fight off the insects, Dr Guenther says. This worsens air quality, at least initially, by increasing levels of ground-level ozone and particulate matter.

The mountain pine beetle, Dendroctonus ponderosae, is a species of bark beetle native to the forests of western North America from Mexico to central British Columbia and Alberta.

Forests in Colorado, Wyoming, and South Dakota are experiencing bark beetle epidemics at a historically unprecedented scale, according to the US Forest Service.

A plan by the Service to deal with the beetles will log, burn, or spray 104,000 acres of lodgepole pines in the Rocky Mountain Region by 2011.

Researchers from the Canadian Forest Service have studied the relationship between the carbon cycle and forest fires, logging and tree deaths.

They conclude that by 2020, the pine beetle outbreak will have released 270 megatonnes of carbon dioxide into the atmosphere from Canadian forests.

The NCAR project, known as BEACHON for Bio-hydro-atmosphere interactions of Energy, Aerosols, Carbon, H2O, Organics and Nitrogen, is funded by the National Science Foundation, NCAR’s sponsor.

BEACHON will allow scientists to gain insights into cloud formation, climate change, and the cycling of gases and particles between the land and the atmosphere, according to Cliff Jacobs, program director in NSF’s Division of Atmospheric Sciences.

The exchange of gases and particles between the surface and the atmosphere is critical in arid areas such as the western United States.

Dr Guenther says even slight changes in precipitation can impact the region.

“Here in the western United States, it is particularly important to understand these subtle impacts on precipitation,” Guenther says. “Rain and snow may become even more scarce in the future as the climate changes, and the growing population wants ever more water.”

Researchers will use aircraft as well as towers that reach above the forest canopy to measure emissions at 100 feet above the ground.

Additional data will come from soil and moisture sensors, instruments for gases and tiny particles, radars, and lidars, which are radar-like devices that use light instead of radio waves.

“BEACHON will give us a very comprehensive picture of a forest’s impact on the atmosphere,” Dr Guenther says.

“But at this point, we don’t know what the project will reveal. We may end up with more questions than answers.”

Organisations participating in the project include Colorado College, Colorado State University, Cornell University, Texas A&M University, and the universities of Colorado, Idaho, Minnesota, New Hampshire, and Washington, as well as the U.S. Forest Service, the U.S. Environmental Protection Agency, and universities in Austria, France and Japan.

Source: ENS

Date: 2/10/2008

Autumn watch on both sides of the Atlantic


Tree lovers on both sides of the Atlantic are able to make sure that they do not miss out on the colourful delights of autumn, thanks to the websites of the US Forest Service and the UK Forestry Commission.

The US Forest Service is offering people a free “hotline”,  which is an automated phone service that will inform callers about the colour of the leaves in the national forests.

Meanwhile in the UK, the Forestry Commission has set up a website that offers a colour-coded website of the commission’s plantations. The website shows what colour the leaves of the various woodlands have reached (ranging from “still green” to “turned golden”).

Although the UK experienced a much wetter than average August, an official for the Forestry Commission said that the woodlands were still “on course” for a colourful autumn.

Source: US Forest Service and UK Forestry Commission websites

Date: 24/09/2008

Old forests ‘continue to capture plenty of carbon’


Planting a new tree may be a less effective way to sequester carbon than saving an old tree from the axe, writes nature.com’s Emma Marris.

A study in the journal Nature shows that old forests continue to accumulate carbon at a much greater rate than researchers had previously thought, making them more important as carbon sinks that must be factored into global climate models.

Until recently, it was assumed that very old forests no longer absorbed carbon.

The only new growth occurred in the small spaces that opened up when large old trees died and decomposed, releasing their accumulated carbon. The forests at large were therefore considered to be carbon neutral, and accounted as such in climate models.

However, in the past decade or so, murmurs of disagreement with this idea have grown louder, and individual projects have found that even very old forests are capable of storing carbon thanks to tree growth, the addition of new trees and a decreased rate of respiration in old trees.

Since the mid 1990s, more sophisticated data collection projects have measured carbon fluxes in forests around the world. In particular, data has been shared between members of FLUXNET, a global network of observatory towers that measure the exchange of carbon dioxide, water vapour and energy between ecosystems and the atmosphere.

Now Sebastiaan Luyssaert of the University of Antwerp, Belgium, and his colleagues have taken advantage of all this new data to produce a meta-analysis of studies that monitored 519 plots of temperate and boreal forest between 15 and 800 years of age.

Their conclusion, published in Nature this week, is that old-growth forests are, in general, still absorbing carbon1. Primary boreal and temperate forests, which make up 15% of global forests, sequester about 1.3 gigatonnes of carbon a year, give or take half a gigatonne. That amounts to about 10% of the global net ecosystem productivity, which was previously accounted for elsewhere].
Dying dogma

The conclusion makes sense, according to Susan Ustin, a plant ecologist at the University of California, Davis. When determining the age of a tree, one counts its rings. Each of those rings represents the transformation of atmospheric carbon into the living tissue of the tree.

In any one year, the death and decomposition of roots or branches may outweigh the carbon sequestered in the trunk – but over time, any significant growth must involve net carbon uptake. “If they are carbon neutral at 400 years old, how are they going to make it to 1,000?” she asks.

“If it was really carbon neutral, the trees would die.”

Overturning the old idea that mature forests are carbon neutral may be the work of more than one paper, and this certainly isn’t the first to propose that they continue to absorb the greenhouse gas. But Luyssaert hopes this analysis will help tip the scales. “Just challenging the dogma isn’t new, but the data that has been used to challenge it was a lot more limited in the past,” he says.

The implications are many. Scientists who were assuming that old-growth was carbon neutral may have consequently been overestimating sequestration in other ecosystems.

Climate models may have to be re-examined. And policies that give credits to governments or companies for sequestering carbon may want to incorporate the protection of old-growth forests into their menu of options.

Indeed, the heartwarmingly green action of planting a tree may actually be second-best to keeping an old tree from the axe: “probably for a couple hundred years, until the young one got big enough to have the same amount of carbon as one of these old trees,” estimates Ustin.

Tim Griffis, a University of Minnesota researcher who mans one of FLUXNET’s observation towers, adds that the work “shows the power of the FLUXNET network”.

But that network is getting harder to operate, as it segues from being cutting-edge research into part of a longer-term dataset. “Many in the community are already finding it difficult to keep their sites funded,” says Griffis.

“I think there does need to be a serious conversation about how we are going to keep this record going.”

Source: Nature.com

Date: 10/09/2008

21-month tree protest ends at US university


A 21-month occupation of an oak grove at the University of California at Berkeley, US, has ended peacefully, but not without some dispute, as the remaining “tree-sitter” protesters descended from their perch, writes AP staff writer MIchelle Locke.

The protesters, who have attracted a considerable amount of media coverage in the US, came down from the trees’ canopies after their food and water supplies were cut off on Monday.

School officials said they were prepared to forcibly remove the activists, who had hoped to stop construction of a $125m (£72.5m) sports centre that threatened a stand of 42 trees on campus.

But as scaffolding took shape at the base of the redwood tree housing the remaining four, the protesters indicated they were willing to descend, said campus police Chief Victoria Harrison. They slowly climbed down early Tuesday afternoon to cheers from supporters below. No one was injured.

The tree-sitters said they agreed to come down on the condition that the University of California create a land use committee that would include input from students and residents into the school’s future land decisions.

But a UC spokesman said there was never such a deal made, and the university has no plans for the committee.

A crowd of several hundred turned out to watch the end of the protest, some drawn by curiosity, others to show support.

A group of street percussionists beat on plastic buckets and water bottles, providing a steady drum beat that competed with the occasional roar of chain saws.

The tree-sitters, none of whom were UC students, were arrested immediately by police and face charges including trespassing and violating a court order, authorities said. Five other demonstrators on the ground also were arrested and face charges including resisting police officers.

Among the bystanders was third-year forestry major Thea Chesney. She agreed with the tree-sitters’ cause, although she acknowledged that made her in the minority on campus.
“It makes me really sad,” she said of the felled trees. “It’s just absolutely tragic what’s happened.”

Source: ABC News website

Date: 10/09/2008

Ancient trees recorded in US mines


Spectacular fossil forests have been found in the coal mines of Illinois by a US-UK team of researchers, writes BBC News science reporter Jonathan Amos.

The group reported one discovery last year, but has since identified a further five examples.

The ancient vegetation – now turned to rock – is visible in the ceilings of mines covering thousands of hectares.

These were among the first forests to evolve on the planet, Dr Howard Falcon-Lang told the British Association Science Festival in Liverpool.

“These are the largest fossil forests found anywhere in the world at any point in geological time,” he told reporters.

“It is quite extraordinary to find a fossil landscape preserved over such a vast area; and we are talking about an area the size of (the British city of) Bristol.”

The forests grew just a few million years apart some 300 million years ago; and are now stacked one on top of another.

It appears the ancient land experienced repeated periods of subsidence and flooding which buried the forests in a vertical sequence.

They have since become visible because of the extensive mining operations in the border area between the states of Illinois, Indiana and Kentucky.

Once the coal seams have been removed (what were, essentially, the compacted soils of the forests), it is possible to go into the tunnels and look up at what would have been lying on the forest floors.

“It’s a really exciting experience to drive down into these mines; it’s pitch black,” the Bristol University research said.

“It’s kind of an odd view looking at a forest bottom-up. You can actually see upright tree stumps that are pointed vertically up above your head with the roots coming down; and adjacent to those tree stumps you see all the litter.

“We found 30m-long trunks that had fallen with their crowns perfectly preserved.”

The researchers believe their study of these ancient forests could give hints to how modern rainforests might react in a warmer world.

The six forests straddle a period in Earth history 306 million years ago that saw a rapid shift from an icehouse climate with big polar ice caps to a greenhouse climate in which the ice caps would have melted.

“The fascinating thing we’ve discovered is that the rainforests dramatically collapse approximately coincident with the greenhouse warming,” explained Dr Falcon-Lang.

“Long-lived forests dominated by giant club moss trees almost overnight (in a geological sense) are replaced by rather weedy fern vegetation.”

The next stage of the research is to try to refine the timings of events all those years ago, and work out the exact environmental conditions that existed. The thresholds that triggered the ancient collapse can then be compared with modern circumstances.

Source: BBC News website

Date: 08/09/2008

Climate change ‘killing California’s trees’


Warmer temperatures and longer dry spells have killed thousands of trees and shrubs in a Southern California mountain range, US research shows.

A study by scientists at the University of California, Irvine also found that the shift in climate had pushed the plants’ habitat an average of 65 metres (213ft) up the mountain over the past 30 years.

A Science Daily report said the study showed that white fir and Jeffrey pine trees died at the lower altitudes of their growth range in the Santa Rosa Mountains, from 1,950 metres to as high as 2,195 metres (6,400 to 7,200ft).

It also found that California lilacs had died out between 1,220 to 1,460 metres (4,000 to 4,800ft).

The researchers also showed that almost all of the plants examined in the study had crept up the mountain by a similar distance, countering the belief that slower-growing trees would move more slowly than faster-growing grasses and wildflowers.

This study, the researchers said, was the first to show directly the impact of climate change on a mountainous ecosystem by physically studying the location of plants.

They added that it offered an insight into what could occur globally if the Earth’s temperature continued to rise.

The finding also had implications for forest management, the team reported, as it ruled out air pollution and fire suppression as main causes of plant death.

“Plants are dying out at the bottom of their ranges, and at the tops of their ranges they seem to be growing in and doing much better,” said lead author Anne Kelly, lead and a graduate student from the university’s Department of Earth System Science.

“The only thing that could explain this happening across the entire face of the mountain would be a change in the local climate.”

The study was published in the online section of the journal Proceedings of the National Academy of Sciences (PNAS).

Source: Science Daily

Date: 15/08/2008

Trees ‘can cut emissions from poultry farms’


Planting just three rows of trees around poultry farms can cut nuisance emissions of dust, ammonia, and odours from poultry houses and help reduce complaints from neighbouring properties, US researchers suggest.

A Science Daily article quotes George Malone from the University of Delaware as saying the tree barrier can cut some of the emissions by almost a half.

Dr Malone presented his findings at the annual conference of the American Chemical Society (ACS).

The team of researchers said planting vegetation could reduce ammonia and particulates that may degrade surrounding air and water quality.

“We were aware of the concerns locally,” said Malone. “We looked at what we could do to address them and the whole area of air quality as it relates to the emission of ammonia from poultry houses.”

In response, they proposed planting trees to serve as a vegetative filter that could capture emissions from family-run farms, which can house an average of 75,000 chickens.

In their six-year study, Dr Malone and his team found that a three-row plot of trees of various species and sizes reduced total dust by 56% percent, ammonia by 53%, and odour levels were cut by about 18%.

However, Dr Malone added that certain tree species were more effective as barriers than others.

“We’ve certainly been on a learning curve since 2001 about the different plant materials suitable for this practice,” he said.

“We typically recommend the first row nearest the fans to be either a deciduous tree or a tree with a waxy leaf surface and the other two rows be an evergreen.

“It’s very important to realise there are a number of criteria that you use in tree selection and planting design. What works for our soil types and climate on the Delmarva Peninsula may not be suitable for other locations.”

The living filter system also has other benefits, the University of Delaware researcher noted.

For instance, it conserves energy by increasing shade and cooling in the summer and acts as a buffer to reduce heating costs in the winter.

Not only do trees enhance air quality, they also improve the water quality around poultry farms because they can filter pollutants from soil and groundwater.

Source: Science Daily

Date: 22/08/2008

US judge overturns wilderness ‘roadless rule’


A US federal judge has overturned a ban on constructing new roads in nearly a third of the US’s national forests, the AP news agency reports.

District Judge Clarence Brimmer issued a permanent injunction against the so-called “roadless rule“, introduced back in 2001 by the Clinton administration, saying it breached the National Environmental Policy Act and Wilderness Act.

The 2001 rule prohibted logging, mining and other developing on 58.5 million acres in 38 states and Puerto Rico.

Judge Brimmer, commenting on the Clinton-era ruling, said: “The Forest Service, in an attempt to bolster an outgoing president’s environmental legacy, rammed through an environmental agenda that itself violates the country’s well-established environmental laws.”

In 2005, the Bush administration replaced it with a procedure that required state governors to petition the US federal government to protect national forests in their states.

However, in 2006, another US District Judge, Elizabeth Laporte in San Francisco, reinstated the 2001 ruling, which led to Wyoming to lodge its complaint.

After Judge Brimmer’s decision, Wyoming Attorney General Bruce Salzburg welcomed the judgement, saying the “roadless rule” jeopardised the well-being of national forests because it was necessary to gain access to deal with beetle infestations and forest fires.

Environmental groups have vowed to challenge the latest ruling, as the ongoing legal battle looks set to continue.

A spokesman for the Wilderness Society said the 2001 position had not changed: “It is not in anyway overturned or compromised by Judge Brimmer’s decision in Wyoming.

“What it does do is create two conflicting court decisions in different federal courts, different states; both issuing decisions with nationwide impacts.”

Source: AP

Date: 13/08/2008

Water’s the limit for Douglas firs


Scientists are betting that you will never find a Douglas fir taller than 138 metres.

Writing in the scientific journal Proceeding of the National Academy of Sciences, a team of researchers found that there was a limit on how high the giant trees were able to pull water up its truck to supply its upper branches.

As the firs reached their physical limit, the upper foliage experienced “drought stress”, struggled to enough water and died back, they explained.

“The trees are moving water purely as a result of physics, ” co-author Barb Lachenbruch, a professor of wood science at Oregon State University, told BBC News.

“The wood has to be designed to be safe at the top of the trees, which means preventing air bubbles getting into the columns that transport the water.”

Tall trees face a greater risk from air bubbles blocking their water supply, known as xylem embolism, because the tension in the columns increases with height as a result of conflicting forces such as gravity.

“If you had a straw that was three feet long and sucked up water before attaching it to the bottom of your tongue, your tongue would be pulled into the straw solely because of the weight of the water in the straw,” Professor Lachenbruch told environment reporter Mark Kinver.

“If you do that with a 300-foot column of water, it would pull incredibly hard; that’s what the force is inside the trees’ cell walls, and that’s why air bubbles can get in.”

The team found that the cellular structure of the wood changed as the height increased in order to prevent air bubbles entering the wood.

“As tree height increases,” they wrote, “the structural modifications needed to satisfy safety requirements eventually will reduce water transport virtually to zero.”

The firs’ wood is mainly made up from dead cells called “tracheids”, which have pits on their sides that act as valves, allowing water to pass from one cell to the next.

The team found that the cells’ pits became increasingly smaller in relation to an increase in height, resulting in less water being transported to the upper reaches of the trunk and branches.

The point where the water supply became non-existent determined the maximum height of the tree, they added.

Professor Lachenbruch said the team calculated this point as being 138m, but added that it could be between 131m and 145m once a margin of error was taken into account.

She observed: “I think it is really remarkable that wood cells, which are about the size of an eyelash but a little bit fatter, with holes on the side can tell us something about how tall a tree can get.”

Source: PNAS/BBC News website

Date: 11/08/2008

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