Not all forests have the same capability for storing carbon. “Forests”, as a generic term for a grouping of trees, inherently demonstrate a wide range of variability; giving rise to the boreal forests of the northern hemisphere, the miombo woodlands of Africa, and the dense rainforests of the Amazon, as a few examples. The level of carbon stored within a forest is highly dependent on the influence of key characteristics such as climate, tree species, and forest structure. Some forests can even be classified as carbon sources (giving out more carbon than they take in!), as opposed to carbon sinks.
We have conducted a short review of some of the relevant parameters:
Trees typically store more carbon than smaller plants. Therefore, a woodland is always a bigger carbon sink of carbon in comparison to grasslands of a similar size, even if it a plantation forest.
The ‘ideal’ tree for carbon storage is one that grows quickly and has a long life, however this combination of characteristics is rarely found in a single species, and for this reason, it is difficult to select a “perfect species”. A fast growing ‘poplar’ might be the best in some areas of the world, but a long living ‘oak’ might be the ideal solution in others.
The ‘perfect species’ for any given forest has to be considered in relation to the geography of its location. When carrying out reforestation it is of fundamental importance to use local non-invasive species because they are better suited to the climate, soil type and geography of the area. Indigenous species also ensure the preservation of local biodiversity. This is particularly true if a mix of species is used which reflects the natural state of tree species diversity – remember different species perform different roles in the forest ecosystem.
2) Forest structure
A dense woodland has more plants and multiple canopy layers, and can therefore store more carbon compared to an area with a sparse tree population. For this reason, forest management needs to maintain a considerable amount of ground cover in order to retain higher levels of carbon storage.
Properly managed forests can function as strong carbon sinks and can simultaneously provide consistent wood production. Forest management that leads to the clearing of large patches of forest, reduces the local biodiversity, and can undesirably transform the forest from a carbon sink into a carbon source.
Although latitude is known to strongly influence the tree species contained of a particular woodland, this parameter also influences many other forest features. For example, climatic regions related to specific latitudes influence the way in which carbon is stored. In boreal forests, more than 80% of carbon is stored in the soil because low temperatures slow down the decomposition of biomass, and therefore reduce the nutrient recycling rate.
Tropical forests instead maintain a warm temperature throughout the year, which causes rapid recycling of nutrients all year round. For this reason the carbon stored in a tropical forest is more or less equally distributed between soil and vegetation.
Calculating the carbon stored in a forest is not a simple task because of the complexity, and influence due to multiple variables. For this reason, Carbomap has spent years working to refine our modus operandi to achieve a high level of accuracy in our carbon calculation.
Author: Sara Ligi
Anon. Which trees offset global warming best? Earth Talk, Environmental Magazine. Available at http://environment.about.com/od/whatyoucando/a/best_trees.htm
Dixon, R.; Brown, S.; Houghton, R.; Solomon, A.; Trexler, M.; Wisniewski, J. 1994. Carbon Pools and Flux of global forest ecosystems. Available online at: http://academic.engr.arizona.edu/HWR/Brooks/GC572-2004/readings/dixon.pdf
Malhi, Y.; Baldocchi, D.; Jarvis,P. 1999. The Carbon Balance of tropical, temperate and boreal forests. Available at: http://www.cnr.berkeley.edu/biometlab/pdf/mahli_pce_1998%2022_715.pdf