Plants are increasingly recognised for their contribution to climate change mitigation, as well as climate change adaptation.
After COP26 in Glasgow, promises have been made for radical changes in policy, regulations, and finance in the race to zero carbon. As commitments escalate to reduce use of fossil fuels and activities that generate carbon emissions, the capacity of plants to sequester and store carbon becomes part of business and policy decisions.
The International Tree Foundation uses a model that estimates that each tree planted in their reforestation projects in Africa sequesters 14.7kg of CO2 each year for 20 years. Trees in urban settings have a more limited capacity to capture carbon, partly because, without correct planting and maintenance procedures, tree growth can be restricted and the data on carbon capture in trees is estimated for a fully grown, mature tree, and partly because of fundamental questions of scale. Results in the USA show that storage of carbon in urban trees lies in the range of 10-30 t per hectare, and sequestration in the range of 0.1-0.9 t per hectare per year depending on tree cover and age. However, urban trees provide multiple benefits. Speaking specifically about urban and peri-urban forests, UNECE reports that a recent study of 1,000 European cities indicates that greening them could save 43,000 human lives annually.
The beech tree, Fagus sylvatica, has a high capacity for carbon storage, achieving an A rating on the Barcham Top Tree Guide. This innovative guide, developed by Europe’s largest tree specialist nursery, provides a score for both species and varieties of trees to enable a more informed selection of trees. The measurement uses data from iTree to estimate dry weight carbon at maturity. Obviously the longer and stronger a tree grows, the greater its ultimate capacity, and the Barcham Top Tree Guide estimates that, for most trees, their life expectancy in urban settings is about half of that in rural landscapes. There is more to the rating than tree age, however, with Liquidambar styraciflua rated with a carbon credit score of B, despite having the same life expectancy as beech. Some of the beech varieties, including Fagus sylvatica Pendula, Fagus sylvatica Purpurea, and Fagus sylvatica Asplenifolia, have the same A rating as the species, despite a shorter life expectancy, while others, such as Fagus sylvatica Black Swan and Fagus sylvatica Dawyck, have a lower carbon credit rating. In urban landscapes beech has many additional benefits, including retention of dead leaves through winter (marcescence), and tolerance to severe pruning which makes it a suitable plant for hedging and for rejuvenation.