Climate change stories are regularly in the news describing how a changing climate could affect humankind in the future. Although trees and woodlands will also be affected by any climate changes as well, they can also play a vital role by combating the causes and effects of climate change by absorbing Carbon Dioxide, which is one of the main greenhouse gases.
Also, trees can be used as an early warning system to help highlight the effects of a changing climate because they will respond to changes in temperatures and light levels with visual signs. For example, if temperatures are slowly getting warmer every year, trees might be expected to come into leaf earlier in the spring. Therefore, if long-term records of tree leaf burst over several years are analysed, they may begin to show patterns of change in our climate. The timing of natural occurences, such as when the first tree leaves open, is called phenology and for several years, there has been an annual phenology survey carried out on some of Exmoor's trees as part of a long-term study.
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How can trees and woodlands help to combat climate change?
The Earth's atmosphere contains gases that trap heat near the Earth's surface. These so-called 'greenhouse gases' are necessary to sustain life on Earth. They let the sun's rays enter the atmosphere but prevent some heat from escaping. This process keeps the planet warm enough to allow life to exist. However, if more greenhouse gases are released into the atmosphere, the greenhouse effect becomes stronger: more heat is trapped and the Earth's climate begins to warm up more quickly. Carbon Dioxide (CO2) is one of the main greenhouse gasses and contributes strongly to the greenhouse effect. It is released to the atmosphere when fossil fuels and organic substances such as wood are burned. However, fossil fuels cannot be replaced in human lifespans but wood is a renewable resource through the replanting of trees or allowing trees to grow back after being felled.
As well as being a renewable resource, trees are also able to reduce the amount of CO2 in the atmosphere by absorbing (or sequestering) carbon during photosynthesis and converting it into sugars which help with tree growth. During this process, the carbon is effectively locked up for the life of the tree and oxygen is released into the atmosphere. In simple terms, the more woodlands that are planted, the more take up of CO2 there will be from trees. However, in order to mitigate the total CO2 emissions of the UK, there would need to be more woodlands planted than there is land available in the UK! Therefore, in order to help combat climate change, the role of woodlands should be considered as a part of a package of measures, including reducing CO2 emissions.
Carbon in Exmoor's woodlands
Within Exmoor, a study entitled, Quantifying Carbon Storage and Sequestration in Woodlands in Exmoor National Park has been commissioned to look at the amount of carbon within the current woodland resource. The draft results indicate the following:
- There are 4,183,840 tCO2(tonnes of CO2) in the existing woodland resource on Exmoor with 18% in conifers and 82% in broadleaves. Most of the stored carbon in Exmoor's trees is stored within oak trees.
- In addition to this figure, there is another 1 million tonnes of CO2 stored in hedgerow trees and free-standing, individual trees.
- The current sequestration rate is around 48,320 tCO2, of which 52% is in conifers and 48% is in broadleaves.
- 25,750 tonnes of CO2are removed every year through harvesting of wood products. This produces annual net sequestration rates of 3.7 tonnes of CO2per hectare for conifers and 3.9 tonnes of CO2 per hectare for broadleaves.
- The net reduction in greenhouse gas emissions resulting from woodland in Exmoor National Park is estimated at 50,230 tCO2 per annum. Of this, 55%comes from conifers and 45% from broadleaves.
- Net carbon gains from three different woodland creation models produced the following estimates:
- Productive conifer woodland = 1351 tCO2
- Native broadleaf = 561 tCO2
- Productive broadleaf = 1027 tCO2
- If there was an equal mix of the three woodland creation models, a planting programme of 180ha per year would produce net emission reductions of 1760 tCO2per year. If this programme was carried on for 20 years, the long term emissions reduction would amount to 35,280 tonnes per year, which is around 10% of the current greenhouse gas emissions (351,772CO2e/yr) within Exmoor National Park.
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