i-Tree Methods & Data FAQs

Where can I find out more about i-Tree methods, science, monetary valuations, equations, or underlying data sources?

Understanding i-Tree summarizes the models underlying the structure, benefits, and monetary value estimates in all the i-Tree tools. It is the best place to start understanding the i-Tree science and provides links to many peer-reviewed publications and white papers for additional details.

Where does the monetary value for carbon benefits provided by trees come from?

Starting in 2025 i-Tree will begin using the estimated 2025 Social Cost of Carbon for the monetary value of carbon storage and sequestration. This value is $130 / metric ton of CO2, and is described in this document from the US EPA. The value represents the midpoint of the 2.5% discount rate estimates for 2020 and 2030. This is an update of the previous Social Cost of Carbon value used in i-Tree which was $51.27 / metric ton of CO2.

What is the difference between “avoided” versus “removed” for benefit values reported?

For carbon dioxide, the “avoided” amounts are related to reduced fossil fuel use due to the energy saving benefits of trees while removed refers to carbon dioxide taken out of the air through photosynthesis and stored in the tissues of the tree. For the pollutants, the amounts refer to either pollutants directly removed by the trees or air pollutants avoided owing to reduced energy use due to the trees' presence.

What is the difference between carbon stored versus carbon sequestered?

Carbon stored refers to the total amount of carbon stored in the tissues of a tree. Carbon sequestered is the amount of carbon dioxide absorbed by trees through photosynthesis from the atmosphere in a given time period. In i-Tree, carbon storage generally refers to a standing stock while carbon sequestration is an annual rate.

What is the difference between avoided runoff and rainfall intercepted?

Rainfall intercepted refers to how much rain directly hits the trees, whereas avoided runoff is a measure of how much rain is not becoming runoff due to the trees’ presence. This measure includes rainfall intercepted and evaporation and transpiration of trees. Without any trees, not all rain would become runoff as some would infiltrate into the soil or be captured in depressions in the landscape.

Is i-Tree applicable to shrubs?

If the shrub species you are interested in is in the i-Tree species list, then you can provide the same basic measurements as you do for trees to get ecosystem service estimates for your shrubs. Additionally, i-Tree Eco supports shrub specific data collection for plot-based projects (see pg. 20 of the Field Guide). Currently, only ecosystems service estimates associated with air pollution and stormwater are estimated for shrubs assessed in this way. Those estimates are grouped with tree ecosystem services, but shrub focused reporting will be added in the future.