Unit 3.1 - W&C - Carbon Stores Flashcards
Where is Carbon stored?
Carbon is stored in ecosystems and biomes such as the world’s tropical rainforest and temperate grassland. When human activity is taken into account, the total amount of carbon stored in the terrestrial biosphere is estimated to be approximately 3,000 GtC. Carbon is an essential plant macronutrient and makes up approximately 44 per cent of the dry weight of plant biomass. Organic carbon is stored in the biomass, leaf litter and soil of terrestrial ecosystems and biomes.
What factors affect the size of a carbon store?
Factors influencing the size of Carbon stores include temperature, precipitation and light.
Define the term ‘biome’.
A plant community whose global distribution corresponds with a climatic region of the Earth, for example the tropical rainforest or Arctic tundra.
How is Carbon stored in a tropical rainforest biome?
Rainforest NPP (Net Primary Production) averages around 2500 grams per square metre per year, and the biomass is 700 tonnes per hectare; this reflects optimum climatic conditions. In total, 550 GtC is stored in tropical rainforest biomass and soil. Large forest trees store 180 tonnes of carbon per hectare above ground and 40 tonnes of carbon per hectare in their roots.
Why do tropical rainforests have such a high level of biomass storage?
Competition for light and water has given rise to five layers of vegetation, including a field layer, shrub layer, under-canopy, continuous canopy (around 30 metres high) and a final layer of emergent trees which project even higher into the sky. Plants are evergreen and so keep their leaves all-year-round. The trees have large leaves. This all helps maximise their rate of photosynthesis and growth. More than two-thirds of the world’s plant species are found in the world’s rainforests. Carbon storage in animals is relatively high in this ecosystem also because the forest provides a large number of habitats where insects, frogs, birds and mammals can live.
Describe Temperate grassland carbon storage.
The lack of rainfall in grassland areas hinders forest growth, with short perennial grasses dominating the landscape. Temperate grassland stores 185 GtC in biomass and soil, with 2-10 tonnes of carbon per hectare above ground and double this amount below ground as roots. Soil carbon stores, consisting of humus, average around 100-200 tonnes per hectare. Mid-latitude temperate grasslands are found on the edge of mid-latitude deserts and on the leeward side of mountain systems, creating a rain shadow. Examples include the North American Prairies and the Eurasian Steppes.
How has deforestation affected carbon stores?
Huge areas of Amazonia have been cleared for commercial agriculture: deforestation averaged around 17,500 km2 per year 1970 -2013. Major crops such as soya beans are grown on old rainforest soils in Brazil; the biomass of soya crop cover is 2.7 tonnes per hectare compared with 180 tonnes per hectare for virgin rainforest. Oil palm cultivation takes place at the expense of tropical rainforest cover, for example in Indonesia.
How can afforestation affect carbon stores?
New trees act as carbon sinks and can therefore help with climate change mitigation.
New monoculture of commercial trees, such as coniferous plantations in the UK, can increase carbon storage if it replaces grassland.
However, plantations store less carbon than natural forest because monoculture forest lacks biodiversity and provides few habitats for other species. Individual citizens can play an active role in afforestation through the practice of carbon offsetting which is another widely-used mitigation strategy that aims to marry businesses principles with environmental goals.
Define the term ‘mitigation’.
Climate change mitigation consists of any action intended to reduce GHG emissions, such as using less fossil fuel-derived energy, thereby helping to slow down and ultimately stop climate change.
Define the term ‘Carbon Offsetting’
Carbon offsetting is a way of compensating for your own emissions by funding an equivalent carbon dioxide saving elsewhere. The idea that we ‘plant a tree’ after taking a flight is an example of the offsetting principle.
How does agriculture affect carbon stores?
Clearing natural vegetation for agriculture brings a large reduction in carbon storage; in many farmed areas, soil carbon levels have fallen by 50 per cent. Soil erosion occurred in the USA during the 1920s and 1930s. In the Great Plains, wind erosion stripped the top soil from 65 million hectares of over-cultivated land, leading to an enormous loss of soil carbon storage capacity. Agriculture which improves the biological productivity of land using irrigation and/or fertilisers may increase local carbon storage (for example, the planting of fruit trees in irrigated semi-arid areas).
