Overview & Applicability
The CUFR Tree Carbon Calculator (CTCC) provides quantitative data on carbon dioxide sequestration and building heating/cooling energy effects provided by individual trees. CTCC outputs can be used to estimate GHG (greenhouse gas) benefits for existing trees or to forecast future benefits. The CTCC is programmed in an Excel spreadsheet and provides carbon-related information for trees located in one of sixteen United States climate zones.
The CTCC was developed as a "proof of concept" software and is provided "as is" without a warranty. It is based on data from 16 references cities and the top 20-25 inventoried tree species from those cities. Updated versions of the underlying growth equations used in the model are becoming available. These new equations are being integrated into tools such as ecoSmart Landscapes and into applications through i-Tree (not yet available).
Inputs and Outputs
The user provides information on the climate zone (one of 16 pre-defined zones), tree species of interest, and tree size (d.b.h.) or age. Tree height can be used in place of d.b.h. for palm species. The CTCC then produces information on:
- Carbon dioxide stored in the tree due to its growth over many years
- Carbon dioxide sequestered during the past year
- Dry weight of aboveground biomass that could be utilized if the tree was removed
If trees are strategically located to shade buildings and reduce energy consumed for heating and cooling, additional inputs are needed along with those listed above. These include tree distance from building, tree direction from building, building age, and type of air conditioning/heating equipment. Default values are provided for cooling (electricity) and heating (natural gas) emissions factors, though these can be customized. CTCC outputs include:
- Annual energy savings in kWh of electricity (cooling) and MBtu or GJ(heating) per tree
- Carbon dioxide equivalents of these energy savings
Restrictions and Limitations
Tree size and growth data are developed from samples of about 650-1000 street trees taken in one reference city for each of the sixteen climate zones. Approximately 20-25 predominant species were selected in each of the sixteen regional reference cities. Many of the biomass equations used to derive total CO2 stored and sequestered are derived from open-grown, city trees.
Conditions may vary within regions, so data from the CTCC may not accurately reflect the rate of tree growth, microclimate, or building characteristics for every city or location within a region. When conditions are different it may be necessary to apply biomass equations manually using adjusted tree growth data, and to perform building energy simulations with modified weather and tree data to more accurately depict effects of trees on GHGs. All equations used in the application are available in the help manual included with the downloaded CTCC.
More accurate and precise growth equations compared to those used in the CTCC are now available. These are being integrated into other applications such as ecoSmart Landscapes (available for California only) and i-Tree (not yet available).
Accessing the tool and additional information
The tool can be downloaded from the link below.
An extensive user guide and help menu is included along with the tool once the CTCC is downloaded. The spreadsheet also provides cell-specific definitions and assistance.