How do trees sequester carbon


How Forests Store Carbon

Increases in carbon dioxide (CO2), and other pollutants in the atmosphere known to affect global climate, has caused some people to become interested in carbon capture and sequestration technology. This includes pumping CO2 underground into old coal mines and aquifers. While these technologies may work, they are still unproven and expensive at larger scales.

Fortunately, the best carbon capture technology has already exists: trees and forests. According to the US Forest Service, America's forests sequester 866 million tons of carbon a year, which is roughly 16% of the US annual emissions (depending on the year). Forests sequester or store carbon mainly in trees and soil. During the process of photosynthesis trees pull carbon out of the atmosphere to make sugar, but they also release carbon dioxide back into the atmosphere through decomposition. Carbon and other gases within forests are captured and released on a cycle. Forest management is able to influence these cycles and enhance carbon capture.

Trees

Trees are without a doubt the best carbon capture technology in the world. When they perform photosynthesis, they pull carbon dioxide out of the air, bind it up in sugar, and release oxygen. Trees use sugar to build wood, branches, and roots. Wood is an incredible carbon sink because it is made entirely of carbon, it lasts for years as a standing tree, and takes years to break down after the tree dies. While trees mainly store carbon, they do release some carbon, such as when their leaves decompose, or their roots burn sugar to capture nutrients and water.

Let's look at a real example, a white oak can live for 200 years; all that time it is pulling carbon out of the air and storing it. After several anthracnose outbreaks the tree dies, but it takes decades for the tree to rot. While it is slowly breaking down, the rotten tree is still keeping carbon out of the atmosphere.

Forests capture and store different amounts of carbon at different speeds depending on the average age of the trees in the stand and the number of trees in the stand. Young forests have many trees and are excellent at capturing carbon. Young trees grow quickly and are able pull in carbon rapidly. Not every small sapling becomes a large tree due to competition for light, resources, and growing space, but when they die and decompose little carbon is released. The trees that remain continue to grow and sequester more carbon as the forest matures.

Established or mature forests are made up of "middle-aged trees", which are medium to large, healthy, and have a large root system. Middle-aged trees grow slower than young trees, but the amount of carbon captured and stored is relatively greater. Some of large trees occasionally die, but they are quickly replaced by younger trees who take advantage of the new space. Since more trees are growing compared to those that are dying, the overall net productivity (how many trees grow versus how many die) is positive and carbon capture is enhanced.

Old-growth forests have a more fixed, or less dynamic, carbon cycle within live and dead trees and the soil. In old growth forests, large trees dominate by shading out small saplings, so recruitment of young trees and net productivity is zero. Still, the carbon is well contained within the big trees, slowly rotting logs, thick leaf litter and soil. Large individual trees may take up as much carbon as an individual middle-age tree, but since there are fewer trees in an old growth stand, the total additional carbon capture is often lower.

Soil

The carbon that is sequestered in forests comes in many forms. For example, forest soils contain plant roots, leaf litter, and other dissolved organic material. The amount of carbon stored in forest soils is variable, and how much carbon soil can sequester is dependent on many local factors like local geology, soil type, and vegetation. In some forests, like in Canada by the tundra, the soil holds more carbon than the trees, but in other forests, like the rain forest, the soil holds relatively little carbon and the trees store more carbon. This is because some soil types, like clay soils, can bind up a large amount of carbon, whereas sandy soils are not able to bind much carbon. Soils with more organic material (bits of wood, decaying leaves, or dead creatures) can store more carbon because organic material easily binds loose carbon molecules and the organic material itself is stored carbon. Soils that are frozen for a good part of the year or have a high-water table can also store large amounts of carbon because decomposition is slow.

Permanence

Besides capturing large amounts of carbon, forests are good at storing it for a long time. However, like all things natural, carbon in forests ultimately gets released into the atmosphere through decomposition, respiration, or other methods. Some places are better at storing carbon for long periods than others; this is called permanence. The carbon that makes up a center of a mature white oak remains bound up for a long time. It has been pulled out of the atmosphere a hundred or more years ago, and it will remain bound up until the tree dies and is decomposed. That process can take decades to centuries depending on how long the tree is alive. Carbon captured by a small trillium has little permanence. Trilliums are annual plants, so the aboveground plant dies annually and rapidly decomposes or they are commonly eaten by deer.

Examples

Let's look at how forest growth and soils affect the permanence of forest carbon. The Amazon rainforest appears to be a good place for carbon sequestration because it is full of big trees that grow rapidly. But research has found the Amazon is a poor carbon sink because there is little permanence. Whole trees rapidly decompose in the hot humid climate, the soils are not able to store a lot of carbon. The near constant rain also helps to break down organic material and wash away soil and nutrients. In contrast, the spruce forests of Alaska are excellent carbon sinks. The spruce grow large, decomposition is slow due to the cold, and the soil is able to lock up carbon in permafrost. Unfortunately, the growth rates in these forests is relatively slow due to the cold temperatures and limited growing season. Changes in global climate are also melting the permafrost, releasing much of the captured carbon. Pennsylvanian forests offer an ideal middle of the road solution. The trees grow well and are long-lived, decomposition occurs at a mild rate, and the soil stores a moderate amount of carbon. This means our forests have great potential to serve as an effective carbon sink and provide long-term carbon storage.

Management Strategies

While carbon capture in trees is a natural process, there are ways to encourage trees to sequester more carbon through forest management. The most important strategy is to keep forests as forests. When forests are converted to other types of land uses, carbon is released and the land loses its potential to store carbon. This does not mean that clear cutting (where silviculturally appropriate) must be stopped. Clear cutting resets the forests age and can in fact accelerate carbon capture by growing younger trees. Climate benefits also occur when timber products displace the use of other products that require the use of fossil fuels (e. g., plastics). When it comes to carbon, the best way to enhance carbon capture without cutting the existing forest is to increase forest cover. This can be done by planting old fields with a mix of native trees or restoring old mine sites.

Controlling invasive plant species is another important strategy for enhancing carbon capture. While many non-native/invasive plant species can grow rapidly and appear to be a good carbon sink, they are not. Invasive species disrupt native ecosystems, change the makeup of the local soil microbes, and prevent tree regeneration, all of which interferes with a forest's ability to sequestration carbon. Native trees and plants are adapted to thrive in local conditions and tend to function better as carbon capture mechanisms. Native plants also provide other important benefits such as wildlife habitat.

Practicing sustainable silviculture is essential for ensuring forests remain healthy and can also help enhance carbon capture. Harvesting is considered sustainable when decisions are based on silvicultural knowledge and follow a long-term management plan. Professional foresters are also important for helping owners meet multiple management objectives while maintaining the value of their stands. Forests that maintain their value are more likely to remain as forests in the future when ownership changes.

Uneven aged stands offer the best carbon capture services, as well as other benefits (e.g., wildlife habitat). In an uneven aged stand, there is continuous recruitment of younger trees, but older trees also remain and help hold carbon for long periods. Uneven aged stand management requires harvesting to occur through single tree or group selection. However, removing individual trees disturbs the soils in the local area. These soils also hold carbon and frequent disturbance over time can turn soils from a carbon sink to a carbon source. To help prevent soil disturbance in these stands it is important to extend the rotation period. For example, a hardwood forest that has been traditionally thinned every 10-15 years should be thinned ever 20-25 years, so the soils have time to recover between entries. In comparison, the rotation of even-aged forests do not need to be extended. In Pennsylvania, these harvests tend to occur every 80 to 100 years, which means the soils can remain undisturbed for long periods.

There are several other best practices you can adopt today for enhancing carbon storage in trees and soils. When harvesting, it is important to reduce damage to the soil. This can be done by putting slash on skid trails, not harvesting in the rain, harvesting in the winter, and using forwarders instead of whole-tree skidding. Harvesting trees that are slowly growing can also contribute to carbon sequestration. Instead of letting mature trees die and decompose, they can be removed and cut into products like 2x4s, flooring, or cabinets which go into homes and buildings and that could be around for centuries. The Liberty Bell is a great example of how high-quality wood products can help store carbon. The wooden yoke of the Liberty Bell is made from American elm harvested in the 1770s (there is some disagree on how old the beam is). Instead of decomposing in a forest centuries ago, the carbon in that wood is still around today holding up the Bell. 

Closing Remarks

Forests are an important carbon sink, as both trees and forest soil are able store large amount of carbon for a long time. However, carbon management is not just about deciding which trees to cut, but also where harvesting and planting occurs on the landscape. It is important to maintain a mix of tree ages and forest types with a focus on young and established forests, as these forests capture and sequester the most carbon. However, this does not mean old-growth forest should be sacrificed to create more young forests. This could release large amounts of carbon, and a new forest would take decades to sequester as much carbon as currently stored in the old-growth forest. The key is to use planning and management strategies that help capture additional carbon while minimizing losses of stored carbon. Professional foresters can help you understand the potential of your land and forests for enhancing carbon capture through forest management, while maintaining the value and health of your forests.

Carbon Sinks and Sequestration | UNECE

Depending on their characteristics and local circumstances, forests can play different roles in the carbon cycle, from net emitters to net sinks of carbon. Forests sequester carbon by capturing carbon dioxide from the atmosphere and transforming it into biomass through photosynthesis. Sequestered carbon is then accumulated in the form of biomass, deadwood, litter and in forest soils. Release of carbon from forest ecosystems results from natural processes (respiration and oxidation) as well as deliberate or unintended results of human activities (i.e. harvesting, fires, deforestation).
 The contribution of forests to carbon cycles has to be evaluated taking also into account the use of harvested wood, e.g. wood products storing carbon for a certain period of time, or energy generation releasing carbon in the atmosphere.
In cases where the net balance of carbon emissions by forests is negative, i. e. carbon sequestration prevails, forests contribute to mitigating carbon emissions by acting as both a carbon reservoir and a tool to sequester additional carbon. In cases when the net balance of carbon emissions is positive, forests contribute to enhancing greenhouse effect and climate change.
Forests and their role in the carbon cycle are affected by changing climatic conditions. Evolutions in rainfall and temperature can have either damaging or beneficial impacts on forest health and productivity, which are very complex to predict. Depending on circumstances, climate change will either reduce or increase carbon sequestration into forests, which causes uncertainty about the extent to which the world’s forests will be able to contribute to climate change mitigation in the long term. Forest management activities have the potential to influence carbon sequestration by stimulating certain processes and mitigating impacts of negative factors.
Forest ecosystems in the European Union play multiple significant roles, including carbon sequestration. It is estimated that the forest biomass in the EU27 countries contains 9.8 billion tons of carbon (tC). The total CO2 emissions of the EU27 countries in 2004 was 1.4 billion tons of carbon . This means that the amount of carbon emitted every year by the EU27 equals to nearly one-seventh of the carbon stored in the EU27 forests. As a result, the value placed on forests in the EU can be seen as a viable way of mitigating GHG emissions through carbon sinks and sequestration.
In the UNECE region as a whole, the carbon stock in forest ecosystems is increasing. Since 1990, the total forest carbon stock in Europe increased by 2 billion tons, i.e. an average of 137 million tons of carbon per year. The main reasons for this increase are policies and legislations that ensure that wood removals do not exceed increment, as well as forest growth rates that have increased in many forest types. Forests and other wooded land in the UNECE countries cover nearly 1.9 billion hectares, located in North America, Europe (including territory of Russian Federation), Caucasus and central Asia . According to FAO’s Forest Resources Assesment, the total carbon content in forest ecosystems for the year 2005 was 638 Gt C (1 Gt C equals to 1 billion metric tons of carbon). Estimates by FAO show that forests in the UNECE region represent approximately 40 percent of all carbon contained in forests. An important feature that distinguishes the region’s carbon stock is a relatively high ratio of carbon stored in soils, nearly half of the total.
In relative numbers, in 2005, North America had an estimated 118 tons of carbon stock per hectare (includes carbon in living biomass, dead wood, litter and soil). Europe had nearly 177 tons of carbon stock per hectare. A trend from 1990 to 2005 shows that many European countries and the U.S. reported significant total carbon stock increases. The trends show an increase of carbon stock in many countries of the UNECE region, and sustainably managed forests could continue to store even more carbon, thus contributing to climate change mitigation.

 

  • UN-REDD Programme

Scientists: plants absorb excess CO2 in large quantities

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Plants take up 16% more carbon than previously thought plants during photosynthesis.

A report published in the journal Proceedings of the National Academy of Sciences claims that plants absorb 16 percent more carbon dioxide during photosynthesis than previously thought.

This fact will help explain why the actual growth of CO2 in the atmosphere turned out to be much less than predicted by the models created by climatologists.

Calculating the amount of carbon dioxide held in the atmosphere is critical to assessing future impacts on global climate.

New Model

Approximately half of the carbon dioxide produced on the planet is dissolved in the oceans or absorbed by living organisms. However, trying to accurately model the global impact, especially for decades to come, is an unimaginably difficult task.

In the current study, American scientists reanalyzed how trees and plants consume carbon dioxide.

By observing how carbon is distributed in leaves, the authors concluded that plants absorb more CO2 than previously stated.

Scientists conclude that in reality the amount of carbon dioxide absorbed by plants turned out to be 16% higher.

At the same time, they say, we are talking only about the period in the last few decades, accompanied by a rapid increase in greenhouse gas emissions into the atmosphere. "How much more noticeable is this difference [between predicted models and real data] if we try to predict the growth of CO2 concentration hundreds of years ahead?" asks Dr. Lianghong Gu of the Oak Ridge National Laboratory in the United States.

Adjustments to be made

Others in the scientific community, while agreeing that the study could indeed help refine existing concepts, do not believe that this is enough to call into question the prospects for global warming as a result of rising concentrations of carbon dioxide in the atmosphere.

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Despite the results of the study, experts still call for a reduction in CO2 emissions

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According to Pap Canedell of the Global Carbon Project at the Australian National Research and Applied Research Facility, a new study shows just how much the subtleties of plant structure can have on global climate processes, according to Pap Canedell.

The expert believes that the uptake of carbon dioxide by plants is just one of many factors influencing climate change. According to him, on the basis of this study, it is still too early to draw a conclusion about what the limiting capacity of terrestrial ecosystems to absorb or process carbon dioxide is and how much this can affect trends in its accumulation in the atmosphere.

Many experts agree that this discovery will require correction of existing climate models.

However, in the long run, more and more reductions in carbon dioxide emissions emitted by humans into the planet's atmosphere will still be required, they believe.

At the end of the summer, another group of American researchers came to the conclusion that the general increase in temperatures associated with global warming may not occur in the next decade. How the oceans save the Earth from overheating0005

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Surely everyone has heard at least once that forests are the “lungs of the planet”, because they produce oxygen and absorb carbon dioxide. In fact, the world's oceans play a leading role in supplying us with oxygen and absorbing carbon. Trees and plants produce only 20% oxygen. The remaining 80% we get from the ocean. More precisely, thanks to the phytoplankton that lives in the ocean.

It is due to the work of phytoplankton and the ocean ecosystem as a whole that the Earth's atmosphere does not heat up too quickly. But humanity, with its oil production, uncontrolled fishing and plastic pollution, is gradually destroying the ocean.

Podcast host — Anastasia Chizhevskaya, founder of the environmental education bureau Sustainble and blogger.

Conversation timeline

0:17 — How forests take in carbon and release oxygen

03:43 — Why forests are still important

05:41 — How the ocean “breathes”

07:55 — What causes the oceans to suffer

13:01 — What can be done to save the ocean

Let’s talk about forests first

Trees absorb carbon dioxide from the air they need carbon to grow. With the help of solar energy, they turn carbon dioxide and water into nutrients, and release oxygen into the atmosphere. On average, for the life of one cubic meter of a tree, about 1 ton of carbon dioxide is needed. As a result of photosynthesis, 700 kg of oxygen enters the atmosphere from this amount of carbon dioxide.

Large tracts of wild forest from 50,000 hectares, in which logging is not carried out, are called "carbon cans". These are, first of all, tropical forests in South America, Africa, Southeast Asia, taiga forests in Russia and Canada. According to Greenpeace, the Amazon forests store between 80 billion and 120 billion tons of carbon. This is a volume equal to 12 years of global emissions.

If you start building roads, cutting trees and mining in such forests, a huge amount of carbon will be released. In addition, as a result of forest fires, the forest turns from a carbon dioxide absorber into its source.

At night, photosynthesis does not occur, and trees consume oxygen. Animals, fungi and bacteria that live in the forest and do not produce oxygen themselves also need to breathe. Also, the forest spends oxygen from the atmosphere on the decomposition of the remains of dead organisms. As a result, forests work as if "to zero", absorbing about the same amount of oxygen as they emit.

How the ocean "breathes"

The ocean absorbs carbon from the surface and stores it in deep waters. It takes about 30% of the carbon emissions that people produce. If not for the oceans, the planet would quickly become too hot for life.

In seawater, carbon molecules are converted into other chemical compounds or serve as food for phytoplankton - single-celled algae and cyanobacteria. Molecules eaten by phytoplankton are separated into oxygen and carbon. Oxygen returns to the water, and carbon accumulates in the growing phytoplankton.

If the ocean stops absorbing and retaining carbon, it will be impossible to slow down global warming.

What is happening to the ocean

According to the UN, already 40% of the world's oceans have been severely affected by human actions . There are two reasons - pollution and depletion of fish stocks.

What pollutes the ocean:

  • oil and oil products;
  • waste water from enterprises where there are heavy metals, mercury and other hazardous substances;
  • agricultural pesticides;
  • plastic waste and lost fishing nets.

It is believed that every minute a truckload of plastic enters the sea. If this continues, by 2050 there will be more plastic in the ocean than fish.

According to the Whale Protection Fund, more than 2.5 thousand dolphins have died in the Black Sea over the past five years due to human actions.

Uncontrolled fishing also causes harm. Overfishing disturbs the natural balance in the ocean ecosystem. In addition, Commercial fishing is generally very inhumane. For example, when trawling, in addition to fish, marine mammals also get into the net, which are of no nutritional value, but still die in the nets. In addition, some countries, such as Japan, still allow whaling.

According to the UN, today 90% of large fish populations are depleted, and 50% of coral reefs are destroyed .

Another problem in the ocean is water acidification. Carbon released into the atmosphere dissolves in sea water and turns into carbonic acid, which makes the water more acidic. Acidification, directly or indirectly through the food chain, affects all ocean life. If the level of water acidification reaches the level at which phytoplankton begins to die, this will acidify the environment even more. This could destroy the entire ocean.

Corals and other marine life are also harmed by sunscreens containing oxybenzone.

What can be done to save the ocean