Human activities increasing carbon sequestration in forests

Jun 13, 2007

Human-caused nitrogen deposition has been indirectly “fertilizing” forests, increasing their growth and sequestering major amounts of carbon, a new study in the journal Nature suggests.

The findings create a more complex view of the carbon cycle in forests, where it was already known that logging or other stand-replacement events – whether natural or not – create periods of 5-20 years when there is a net release of carbon dioxide from forests to the atmosphere, instead of sequestration as they do later on.

The end result is a highly variable forest carbon cycle that appears to be heavily influenced by the footprint of humans, one way or another. It’s a complicated process with powerful driving forces that were poorly understood, said scientists from 10 institutions in the U.S., Canada and Europe.

Until this report, researchers had never quantified the effect of continuous low levels of nitrogen deposition – about 5-10 percent of the amount used by a farmer each year - to spur net carbon uptake by forests and actually offset a significant amount of greenhouse gases into the atmosphere.

This broad study analyzed the carbon balance across a network of forest sites that represent nitrogen deposition in most of Western Europe and the continental United States. Until now, it has been difficult to separate the effects of nitrogen deposition on forests from the many other variables that affect their carbon release or sequestration – things like forest age, logging, wildfires, disease or insect epidemics, or other causes. This study attempted to do that, and found that the net carbon sequestration by temperate and boreal forests was overwhelmingly determined by nitrogen inputs.

“What is surprising is that the net sequestration is quite large for a relatively low level of nitrogen addition,” said Beverly Law, a professor of forest science at Oregon State University, co-author of the study and director of the AmeriFlux monitoring network in North and South America.

“Through our forests, fertilization by nitrogen deposition is to some degree offsetting our carbon dioxide emissions – at least right now,” she said.

It was first recognized in the 1980s that human activities, by releasing unprecedented amounts of active nitrogen into the atmosphere, were not just altering the global nitrogen cycle but also causing the eutrophication of large parts of the biosphere, the researchers said in their report. Nitrogen – produced by automobile engines, factories, and intensive agriculture – is often a key, limiting nutrient in forests and other ecosystems.

Early forest growth puts a severe nitrogen stress on the ecosystem initially, and then the forest continues to grow and remove carbon from the atmosphere for the rest of the management or life cycle, accumulating wood at a high rate on the small additional nitrogen inputs.

This growth and sequestration is achieved without applications of fertilizer that would likely result in nitrous oxide emissions, another greenhouse gas, that would offset the benefits to the atmosphere of carbon removal.

However, it’s known that large additions of nitrogen to ecosystems can also be damaging above a certain threshold, researchers say, and it’s unclear how long this process will continue.

“The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly through forest management or indirectly through nitrogen deposition,” the study authors said.

Ultimately, mature forests, at least in northern latitudes, absorb and sequester substantial amounts of carbon from the atmosphere. Forest protection and management options have been viewed as one mechanism to absorb carbon dioxide from the atmosphere and reduce concerns about the greenhouse effect and global warming.

Source: Oregon State University

Explore further: Location matters in the lowland Amazon

Related Stories

California farmers agree to drastically cut water use

3 hours ago

California farmers who hold some of the state's strongest water rights avoided the threat of deep mandatory cuts when the state accepted their proposal to voluntarily reduce consumption by 25 percent amid ...

Apple may deliver ways to rev up the iPad, report says

3 hours ago

MacRumors last month said that the latest numbers from market research firm IDC's Worldwide Quarterly Tablet Tracker revealed Apple stayed on as the largest vendor in a declining tablet market. The iPad ...

Architects to hatch Ecocapsule as low-energy house

9 minutes ago

Where people call home depends on varied factors, from poverty level to personal philosophy to vanity to community pressure. Ecocapsule appears to be the result of special factors, a team of architects applying ...

Recommended for you

Location matters in the lowland Amazon

15 hours ago

You know the old saying: Location, location, location? It turns out that it applies to the Amazon rainforest, too. New work from Carnegie's Greg Asner illustrates a hidden tapestry of chemical variation across ...

Image: Cambodian rivers from orbit

May 22, 2015

A flooded landscape in Cambodia between the Mekong River (right) and Tonlé Sap river (left) is pictured by Japan's ALOS satellite. The centre of this image is about 30 km north of the centre of the country's ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

lengould100
not rated yet Aug 25, 2009
The only problem with this theory is that, regardless of the effects of nitrogen on forests, the atmospheric CO2 levels measured on Mauna Loa now are at more than 380 ppmv.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.