In a previous post we saw the various aspects of trees to take into account to see what category it is. Now that we have some idea of the different types of trees, let's dive deeper into how benefits are calculated. A major player in the Netherlands is i-Tree who published a guide on calculating tree benefits with a great visual example of the extent that larger trees are performing compared to smaller trees. One example shows a chestnut with the circumference of 169 smaller trees combined.
Once you know the tree specifics, you can calculate benefits. These include air pollution removal, CO2 sequestration, food provisioning, oxygen production, stream flow and water quality improvement, volatile organic compounds removal, mitigating UV radiation, and providing wildlife habitat. Other benefits are still in development since the calculations are more complex, such as human health benefits. Details are described in the guide here.
How this is converted to financial gains is a bit of a mystery, mostly because prices vary from year to year, and sometimes policymakers prefer to rely on actual benefits rather than prevented costs. You can test this on a small scale, once for free, with this software. The WUR also has a guide that you can fill out yourself, depending on the species of tree. Note that this guide is not dependent on a tree's benefits! So it is still difficult to look at an individual tree and go, that's x euro of ecosystem services. Luckily there has been a study testing individual trees and the i-Tree method. This shows a big difference in annual tree benefits in US dollars depending on size (small trees - height less than 7 m with crown diameter < 5 m; medium trees - height 8–15 m, crown diameter 6–10 m; large trees - height over 15 m and crown diameter > 10 m.)
The first two trees below would provide services that are about 3-4 dollars worth every year, and the next two are about medium sized for canopy and could be 14-19 dollars. It seems a low amount given the costs to grow and place a tree, and the wide amount of services they provide and issues they help prevent. Or, much like water and sunlight, we might not value these services that we get for 'free' as much as they should be.
