Birmingham i-Tree Report

Headline Figures

Table 1: Headline figures for The West Midlands and a comparison of outputs from the component i-Tree Eco studies.

Reference Values and Methodology Notes for Calculations:

• Number of Trees: The sample inventory figures are estimated by extrapolation from the sample plots. For further details see the methodology section.

• Tree Canopy/Shrub Cover: The area of ground covered by the leaves of trees and shrubs when viewed from above (not to be confused with leaf area which is the total surface area of leaves). As shrubs can be underneath trees, these two figures ‘overlap’ and therefore should not be added together. There are different methods for estimating tree canopy cover. It is important to note that these different approaches will produce different results. This depends on the methodology, the definition of what constitutes ‘cover’ (trees, trees and shrubs, trees, green-space and shrubs, etc) and the resolution of the data (leaf on vs leaf off, aerial photos vs satellite imagery vs ocular estimates, etc). Therefore, each study must be interpreted in context with consideration for the expected statistical accuracy.

• Replacement Cost: The cost of having to replace a tree with a similar tree using the Council of Tree and Landscape Appraisers (CTLA) methodology from the Royal Institute of Chartered Surveyors.

• Capital Asset Value for Amenity Trees (CAVAT): A valuation method with a similar basis to the CTLA Trunk Formula Method, but one developed in the UK to express a tree’s contribution to public amenity and its prominence in the urban landscape. For i-Tree Eco studies the amended quick method is used.

• Carbon Storage: The amount of carbon bound up in the aboveground and below-ground parts of woody vegetation.

• Carbon Sequestration: The annual removal of carbon dioxide from the air by plants. Carbon storage and carbon sequestration values are calculated based on the CO2 equivalent multiplied by the Department for Energy Security & Net Zero and Department for Business, Energy & Industrial Strategy figures for the non-traded central estimate cost of CO2. This is currently £265 per metric ton for 2023.

• Pollution Removal: This value is calculated based on the 2020 UK social damage costs for ‘Road Transport Inner Conurbation’; nitrogen dioxide - £24.781 per kg, sulphur dioxide - £7.064 per kg, particulate matter less than 2.5 microns - £473.577 per kg.

• Avoided Run-off: Based on the amount of water held in the tree canopy and re-evaporated after the rainfall event. The value is based on a volumetric charge from Severn Trent Water of £1.6142 per cubic metre and includes the cost of avoided energy and associated greenhouse gas emissions.

• Total Annual Benefits: Sum of the annual monetary values of carbon sequestration, pollution removal and avoided run-off. Carbon storage is not included since it is not an annual benefit, rather it is a portion of all of the carbon that has been sequestered over the lifespan of the tree.

Data was processed using iTree Eco Version 6.0.32.