i-Tree report values London’s urban trees at £6bn

Urban trees can provide a range of beneficial services, such as masking noise, providing natural flood defences and absorbing pollution.  While there is widespread public appreciation of urban trees, the full range of benefits are often unnoticed and undervalued.  Recognising and assessing the importance of these benefits can help to make decisions about the best way to manage urban trees.  Last month, the London i-Tree Eco Urban Forest Survey was released.  Using 300 volunteers, it is the most extensive urban tree survey carried out in the world to date.  The report quantifies the benefits of urban forests and highlights the need to manage existing trees as well as planting new ones to ensure that these benefits are maintained for future generations.

The assessment, carried out by the RE: LEAF partnership uses the i-Tree Eco Tool, which is a software model that is designed to use field data from complete inventories or random plots throughout a community, along with meteorological data in order to quantify urban forest structure, value to communities and environmental effects.  However, it does not quantify all ecosystem services provided by urban trees, such as soil formation and protection, education and habitats for species and as such should be “recognised as a conservative estimate of the total value of the full range of benefits that the urban forest provides to Londoner’s”.

With approximately 8.5 million trees worth £6.1 billion to London, the wider ecosystem services, including storm water alleviation, carbon storage and pollution removal have been quantified within the report.  In particular, flood and air pollution were some of the key benefits revealed in the survey results.  For example, removal of pollution is estimated at 2,241 tonnes with a value of £126 million per annum.  This can be further broken down using i-Tree into each pollutant and by inner, Outer and Greater London with removal the greatest for ozone.

Current levels of heavy rain have resulted in storm water run-off and river breaches which have been largely responsible for severe flooding episodes across many parts of the UK.  Future climate change predictions are suggesting that extreme weather events will become more frequent.  According to the study, the quantifiable benefit of trees to mitigate this will be of significant value in supporting the case for increased planting and maintenance as well as appropriate selection of species.  It has calculated that the trees within Greater London have an equivalent leaf area of approximately 1047km² which prevents the runoff of 3,414,000m³ per annum, predicted to be worth £2.8 million.

Trees can help to mitigate climate change by sequestering carbon as part of the carbon cycle.  The net sequestration of London’s trees has been estimated by the report at 65,534 tonnes of carbon per year, with a value of £3.9 million per year.  Carbon storage refers to the amount of carbon tied up in above and below ground parts of woody vegetation.  An estimated 2,367,000 tonnes of carbon is stored in London’s trees, valued at £147 million.  Within this urban forest, Oak as a species stores the greatest amount of carbon.

The results presented in the report will be used to inform the next London Environment Strategy as well as the next iteration of the London Plan.

The full report as well and the raw data are publicly available to download on the i-Tree website.

Source: Forestry Commission