Tree Carbon Performance Certificates

Barcham Carbon Performance Project

The Barcham Carbon Performance Project has applied a rating to all trees in the nursery catalogue, classifying them by their ability to absorb carbon.

Trees provide many benefits, seen and unseen.  They are great at improving air quality, absorbing carbon, protecting our watercourses, providing habitats for wildlife, and for adding aesthetic value.  They also deliver huge environmental benefits, known as ‘ecosystem services’, which contribute daily to the health and wellbeing of our planet.

One such ecosystem service, and perhaps the one we are most familiar with, is trees’ ability to suck up carbon from the atmosphere and store it within their woody structures.  This all occurs during the process of photosynthesis, where trees absorb carbon dioxide, release oxygen and store carbon.  By offsetting carbon emissions produced by human activities, every tree planted is a credit to the environment as it can help towards mitigating climate change, ensuring more carbon is stored than released.

By creating a performance certificate for each tree in the Barcham catalogue, we could illustrate exactly what each tree will be able to deliver, in terms of carbon capture. These certificates allow for an easy comparison of carbon storage between different species and varieties. Our ratings range from the top environmental ‘A’ grade to the less contributing ‘E’ grade. The larger woody trees are all within the A-C grades with smaller trees and shrubs making up the lower grades. Sycamore is an ‘A’ grade environmental asset whilst a Crab Apple is a ‘C’ grade. However, it is not always a case of choosing a species with a higher carbon capture; trees should also be selected based on the conditions they will be growing in.  A poor scenario is to plant an ‘A’ grader, such as a Sycamore, in a confined space so it can never fulfil its potential.

But the right tree, in the right place, when given the right care, can be a huge asset.

Click here, to see an example of the many hundreds of carbon performance certificates created for this project.

How does Treeconomics model tree benefits?

Over the past 10 years, measurements from thousands of urban trees have been collected in towns and cities across the UK by Treeconomics and its project partners.

The DBH (diameter at breast height) of any given tree can be used to estimate carbon storage.  Maximum DBH was estimated for each species from peer reviewed academic literature, or by using a height regression table, determined by the tree’s height and its stature (small, medium, large).  In cases where this data was available, estimates from tree experts were used based on maximum life expectancy.


All species and varieties were run through the i-Tree Eco v6.0.21 model.  i-Tree Eco is a peer-reviewed, open source and freely available software suite, developed by the United States Forestry Service (USFS)3.  It is used internationally to assess urban trees and calculate their benefits to society.  This tool was used to calculate carbon storage from each species and variety based on the expected DBH a tree would reach within its lifetime.

The results for all these trees were sorted by both species and size. The trees were then grouped into like-for-like sizes before being ranked for their performance against each other. However, for less common trees there are simply not enough records to obtain sufficient data. In these instances the data was modelled based on the following steps…


1. Growth rates were assigned to each species, depending on the growing speed of the tree, which was estimated using Barcham’s catalogue information, other online tree nurseries, and the PFAF database (Slow/Medium/Fast).

2. This allowed for calculation of estimated DBH at different age classes. These begin at 0, and increase by 10 up to 50 years, and thereafter: 75, 100, 150, 200, 250 and 300. The data ends at the life expectancy of the tree (provided by Barcham).

3. By running each species through i-Tree, the carbon storage at each age could be determined. This was plotted on a graph, to show the changing rate of carbon storage as a tree grows. A polynomial line of best fit was applied for interpretation at other ages.

4. The graph also indicates the carbon cost of a tree, which is calculated to be 2.6kg¹.
It should be noted that while i-Tree includes the majority of subspecies, it does not account for all. In these cases, reference should be made to the main species.

5. The subspecies to which this applies are:

Catalpa bignonioides: Aurea
Cedrus deodara: Aurea
Cornus controversa: Variegata
Cornus kousa: China girl, Chinensis, Stella Pink
Crataegus monogyna: Alboplena
Fagus sylvatica: Asplemifolia, Black Swan, Dawyck, Dawyck Gold, Dawyck Purple, Pendula, Purpurea, Rohan Obelisk, Rohanii, Roseomarginata, Tricolor, Zlatia
Magnolia grandiflora: Gallissoniere, Praecox
Morus alba: fruitless, pendula, platanifolia

6. In addition, Laburnocytisus Adamii is not included in i-Tree. In this case, data is taken from an input of Laburnum anagyroides.

7. Species were ranked based on their average carbon storage, and categorised into A,B,C,D,E and F. The ‘carbon break even point’ with how much carbon is produced in their production is given.

8. The age at which this occurs was determined using an interpolation equation to provide a value between two known values:y = y1 + ((x – x1) / (x2 – x1)) * (y2 – y1), ‘where x is the known value, y is the unknown value, x1 and y1 are the coordinates that are below the known x value, and x2 and y2 are the coordinates that are above the x value’

9. Carbon storage (kg/yr) at maturity, being their maximum life expectancy, is also given.

¹ Based on single tree delivery and a 350 mile return trip to the nursery.

Caveats and assumptions

The ratings are given for ‘ideal’ trees growing with adequate soil volume, access to sunlight and without any competition or other limiting factors such as the soil nutrient regime.  Site conditions and soil types vary considerably from site to site and therefore, depending on where and how your tree is planted, the figures quoted may vary.

For some varieties, data was not available and the modelling was therefore carried out at the species level.

Trees confer many other benefits and therefore these carbon values should be considered as a conservative estimate of the total benefits provided by trees.

Please refer to the Barcham catalogue to see their full range of trees and the related carbon performance certificates.

Interested in carbon performance certificates for your own tree nursery?  We’d love to hear from you!