Please donate to support our ‘Plants to Save the Planet’ Project. The Project is directed at enabling designers of ‘carbon farms’ and ‘food forests’: agroecosystems of perennial plants, to choose the most appropriate plants for their requirements and site conditions. We are working on a subset of plants in the PFAF database identified as having the most potential for inclusion in such designs. We are adding search terms and icons to those plants pages, and providing a range of search options aligned to categories of plants and crop yields, with Help facilities including videos. More >>>

Follow Us:

 

Carbon Sequestration

Plants have the potential to save the planet through the process of photosynthesis removing carbon dioxide from the atmosphere, reversing the build-up from burning fossil fuels which is causing climate heating. Perennial woody plants such as trees and shrubs store the carbon long term, especially if they are part of permanent ecosystems where soil disturbance is minimised, so that carbon is also stored long term in soils. The planet saving potential of trees and soils is becoming widely recognised, with tree planting and rewilding schemes being promoted for carbon offsetting.

Plants to Save the Planet

Plants For A Future (PFAF) started the project we now call ‘Plants to Save the Planet’ (PSP) three years ago. We realised that the plants information and search facilities we provide could be part of a global movement to shift public focus from issues concerning people and animals onto recognising the power and importance of plants. Since we started PSP we have extended our database of 8000 useful plants, adding around 700 species suitable for tropical situations. We have also introduced search terms, ‘glossary items’, to enable designers to identify plants which are most suitable for designs with the following aims: Carbon Sequestration, Carbon Farming and Food Forests.

Carbon Sequestration in Plants and Soil

Understanding the carbon cycle on our planet is crucial to combat our climate crisis. In our gardens, and on our farms, we can make choices that increase the rate of carbon sequestration over land. By increasing carbon sequestration in plants and soil, we can work to regain balance in our planet's carbon cycle. Carbon-conscious gardening and carbon farming are crucial tools in climate change mitigation.

Carbon is present in the atmosphere, in the ground, in oceans and in living organic materials. It is exchanged between these different reservoirs through a wide range of natural processes. Without human interference, the natural flow of carbon would keep levels reasonably stable, and the carbon cycle would remain in harmonious balance. According to the Salk Institute, every year plants and other photosynthetic life capture 746 gigatons of CO2 and then release 727 gigatons of CO2 back.

Unfortunately, human activity has dramatically increased the amounts of carbon (approximately 37 gigatons) that is released into the atmosphere annually. This imbalance in the carbon cycle is one of the main contributing factors to the greenhouse effect and global warming.

We can help to redress the balance by:

  • Choosing the right plants – to sequester as much carbon as possible, for as long as possible.
  • Caring for the soil to boost its carbon capture capability.
  • Protecting and restoring existing carbon sink ecosystems around the globe.

In this article, we'll delve into this topic in more depth, to example, what exactly gardeners and growers can do, and what we can all do to make a difference.

Trees: Natures Most Efficient Carbon Sinks

Most people are aware that planting trees is a good thing in climate change mitigation efforts. Trees take carbon from the air through the process of photosynthesis and store it as lignin in their trunks, roots and branches. This means that trees are able to turn CO2, from the atmosphere, into a very stable form of elemental carbon.

Determining how much carbon an individual tree can sequester each year, and over its lifetime, is a complex business. Carbon sequestration rates are influenced by the species of tree, its size and age, temperatures and many other environmental factors. Even the best figures are only estimations, and it is difficult to get accurate figures. These figures are always extremely variable and will be accurate only for the very specific area where they were taken.

Generally speaking; however, all trees have an astonishing capacity to store carbon while in growth. Research has shown that all tree species absorb CO2 from planting to old age (200 years plus). However, they reach their peak in terms of carbon sequestration in their 'teenage' years (from 10-45 years after planting). https://www.farmcarbontoolkit.org.uk/toolkit/sequestration-farm-biomass

Trees are particularly useful for carbon sequestration due to their size, large root structures, and because they are perennial, and will not die back each year. But it is important to remember that the benefits will be lost when trees are chopped down, and the CO2 will return to the atmosphere if the material is then burned.

So trees that are planted for carbon sequestration purposes must remain in place. Permanency in plantations is a crucial component of climate mitigation.

The Best Trees For Carbon Sequestration

Which trees will be best for carbon sequestration will definitely depend on where exactly you live, and the options best suited to your situation and climate. The best options to look for are those that grow quickly and live for a long time. Of course, trees generally don't have both of these attributes at the same time.

Carbon capture schemes often favour younger trees, which grow more quickly. But slower growing trees can sequester much more carbon over their considerably longer lives. The best strategy, therefore, from an environmental standpoint, is generally to plant a number of different tree species, to maximize shorter and longer-term sequestration.

Different studies have identified different trees that are especially good at sequestering carbon in different bioregions. For example, a 2001 study identified horse-chestnut, pines, oaks, plane trees, sweetgums, and bald cypress as good choices for urban trees in the US. https://www.nrs.fs.fed.us/pubs/jrnl/2002/ne_2002_nowak_002.pdf

Method for Calculating Carbon Sequestration by Trees in Urban and Suburban Settings can be found on the EPA.gov website. https://www3.epa.gov/climatechange/Downloads/method-calculating-carbon-sequestration-trees-urban-and-suburban-settings.pdf

Setting and environmental conditions are very important. But so too are human considerations. The best trees to plant will often be those which serve other benefits to humanity. Quite frankly, this limits the possibility that these trees will be chopped down. Fruit and nut trees are therefore often good choices since they can serve multiple functions at the same time.

Forest or Woodland Management For Carbon Sequestration

The key thing to remember when planting trees for carbon sequestration is that afforestation is about more than just trees. While trees are important for carbon sequestration, they are only one part of the complex and balanced ecosystems that help to maintain natural cycles on Earth. There is a danger that we do not see the forest for the trees. A forest is a complex web of life, each element of which is required for maximum carbon sequestration.

Careful management of forest or woodland can result in systems that are far more than just tree plantations. As well as increasing biodiversity, a true forest or woodland system can have layers of planting and complex systems which increase the amount of carbon sequestration overall.

Traditional orchards are often laid out with grass sward beneath the trees. The grass ground cover protects the soil while trees absorb carbon. However, while this cover can be beneficial, a mixed ground cover with nitrogen-fixing plants and guilds of beneficial planting in layers around the trees will increase carbon sequestration overall and create a more dynamic and stable ecosystem. Orchard or woodland management that incorporates carbon trapping trees with layers of other beneficial plants is usually referred to as forest gardening, or, on the larger scale, agroforestry.

In woodland and forest systems managed by humans for human benefit can also include coppicing. Coppicing can be used to maintain systems which sequester plenty of carbon whilst also allowing humans to harvest timber of various uses. In such systems, less land must be given over to trees for the same carbon benefit.

Carbon Sequestration in Bamboo

Trees are not the only plants of interest when discussing carbon sequestration. Bamboo is another plant which is believed to have impressive carbon capture potential. Bamboo has received a lot of attention in sustainability circles in recent years.

Giant, woody bamboos share characteristics with trees and have impressive carbon sequestering capabilities. Again, there is a range of factors that can influence bamboo's rates of carbon sequestration, and notes of caution have been raised about putting too much trust in the results of individual studies.

But living bamboo has been shown to store a similar amount of carbon to tree plantations: from around 100 to 400 tonnes of carbon per hectare. And like wood, it has the capacity to replace other carbon costly products and, when managed and used effectively, can keep carbon from the atmosphere for a significant length of time. https://www.inbar.int/understanding-bamboos-climate-change-potential/

Shrubs and Hedges

Often overlooked in favour of larger carbon-capturing trees, shrubs and hedgerows can also play an important role in increasing the carbon capture capabilities of a piece of land. As permanent, perennial features of an agricultural landscape, or a garden, shrubs and hedges are vital to carbon conscious land management. The wider and higher a hedge, the more carbon it will generally sequester. But careful design and management of mixed hedgerow systems can also help to improve overall carbon sequestration.

Deep Rooted Perennial Plants

All plants will help is sequestering carbon to some degree. But those with deep tap roots will store that carbon more effective within the soil. Other perennial plants, especially those with deep, thick roots, therefore, are also effective in land management for carbon sequestration. Since those deep, woody roots will generally remain in place for quite some time, they should help keep that carbon locked up below the soil for years to come.

Carbon Sequestration in Annual Crops

Annual crops typically have lower root biomass than perennials because they do not need to store energy in the same way. On average, plants allocate 76% of carbon stocks to shoots and only 24% to the roots. However, this can vary considerably due to different climates and environmental conditions. https://www.fcrn.org.uk/research-library/what-crop-type-atmospheric-carbon-sequestration-results-global-data-analysis

What happens next to the biomass generated will determine how much carbon is sequestered in annual arable agriculture or a fruit and vegetable garden.

Interestingly, scientists are looking into how plants can be engineered for larger roots that will store more CO2 and remain and gradually break down to deposit carbon back in the soil. Getting these plants into the global agricultural food chain could potentially contribute a 20 to 46 per cent reduction in excess CO2emissions annually. https://www.wired.com/story/the-plan-to-grab-the-worlds-carbon-with-supercharged-plants/

Short term, there is a lot that farmers and gardeners can do to increase carbon sequestration when growing annual crops. First of all, it is a good idea to incorporate perennial plants into annual food production, through forest gardening or agroforestry, polycultures (mixed planting schemes rather than mono-crop planting). And by maintaining crop cover throughout the year through the use of cover crops and successional planting.

Carbon Sequestration in Soil

So far, we've looked at carbon sequestration in plants. But it is important to remember that soils hold four times the amount of carbon stored in the atmosphere, and more than is held in vegetation. https://doi.org/10.3390%2Fsoilsystems2040064

Modification of agricultural and gardening practices is a recognized method of carbon sequestration. Soil can act as an effective carbon sink, offsetting a significant proportion of carbon dioxide emissions annually.

But how well it sequesters carbon depends on how land is used. Land used for annual cropping is depleted in soil organic carbon, as the carbon-rich biomass of the crops is harvested and removed. Tilling and cultivation also reduce the carbon stored, releasing CO2 into the atmosphere.

Carbon Farming and Gardening Practices – Increasing the Soil's Capacity to Store Carbon

Farmers and gardeners can do a lot, not only to maximize carbon sequestration in plants but also in the soil.

Measures to increase soil carbon include:

  • Chopping and incorporating 'green manures'.
  • Adding compost/ manures (brown organic matter).
  • Incorporating biochar (black organic matter) into the soil.
  • Boosting microbial/ fungal life in the soil and protecting the fragile soil web.
  • Effective crop management, crop rotation and diverse planting schemes.

They can also do a lot to minimize losses of carbon from the soil. Losses are minimized by:

  • Minimal cultivation/ cultivation at shallower depths ('no till'/ 'no dig' practices).
  • Careful use of farm machinery, and reduction of foot and vehicular traffic over the soil.
  • Avoidance of overstocking of livestock and careful livestock management.
  • Management of soil to avoid erosion and compaction at all times.

As well as through careful and appropriate planting.

The Importance of Ecosystem Protection and Restoration

So far, we've focussed on carbon sequestration in plants and soil in human-managed/ cultivated systems. But of course, carbon sequestration in wilder and more natural environments is also hugely important.

Reforestation, ecosystem restoration and tree planting will definitely play a role in tackling our climate crisis. Both protecting existing forests and restoring degraded wooded ecosystems is crucial to carbon sequestration. Though not a panacea, reforestation and afforestation will play an important role in combatting the climate crisis.

Ecosystem conservation is not only about forests and woodlands, however. Wetlands store 14.5% of the world's soil carbon, and yet they cover only 6% of its total land area. Effective protection and restoration of wetlands, therefore, is crucial to climate crisis mitigation and adaptation. https://www.sciencedirect.com/science/article/abs/pii/S0925857417303658

Carbon sequestration is a complex business. The exact levels of sequestration and the best strategies for combatting our climate crisis are under debate. But what is clear is that we need to work with nature, rather than fighting it, if humanity is to have a sustainable and ethical future on this planet. And understanding the carbon cycle and our role in throwing it out of balance – and bringing it back into balance in future – is a good place to start.

 

© 2010, Plants For A Future. Plants For A Future is a charitable company limited by guarantee, registered in England and Wales. Charity No. 1057719, Company No. 3204567. This work is licensed under a Creative Commons License. Some information cannot be used for commercial reasons or be modified (but some can). Please view the copyright link for more information.
Web Design & Management