Trees provide multiple benefits and costs to society that should be considered in planning for the future.
Benefits include moderating climate, lowering energy use in buildings, reducing atmospheric carbon dioxide (CO2), improving air and water quality, mitigating rainfall runoff and flooding, enhancing aesthetics, human health and social well-being, as well as lowering noise impacts.
Trees also have various costs associated with planting, maintenance, and removal. There are indirect costs such as allergies from tree pollen, increases in winter building energy use due to shading from both evergreen and deciduous trees, changes in local biodiversity due to invasive plants, and increased taxes from increased property values.
Annually, urban trees in the United States produce a total of $18.3 billion in positive value related to air pollution removal ($5.4 billion), reduced building energy use ($5.4 billion), carbon sequestration ($4.8 billion) and avoided pollutant emissions ($2.7 billion) (Nowak and Greenfield).
To help assess the value of trees and aid in tree planning and management, a free suite of software was developed by the USDA Forest Service, Davey Tree, and their collaborators.
This software suite, i-Tree, offers specific tools that quantify various services and values derived from trees. These tools range from a simple phone app (MyTree) to sophisticated ecosystem service programs (e.g., i-Tree Eco and i-Tree Hydro).
One of the most recent tools, i-Tree Landscape, is an easy-to-use web-based application that can help to improve landscape management and planning, and easily engage stakeholders in planning prioritizations and decisions.
These images, captured from i-Tree, show examples of surface temperature maps (left) and prioritization maps (right).
i-Tree Landscape allows users to quickly explore tree canopy, forest information, land cover, and basic human demographic information anywhere in the conterminous U.S. Users select their area of interest and can compare results among various areas (e.g., Census block groups, Census places, Congressional Districts, county, state, HUC 12 watersheds).
With the information provided by i-Tree Landscape, users learn about the benefits and values (carbon storage, air pollution removal, reduced runoff) of trees in their area, as well as local risks to people and forests, such as:
- insects and diseases
- wildfire potential
- wildland-urban interface
- ultraviolet radiation exposure
- air pollution exposure and poor air quality
- surface temperatures
- future ozone concentrations
- climate change
By understanding the value of trees and various risks to both people and trees, this tool facilitates planning efforts by determining and targeting priority locations with the greatest value and/or risks. These priority locations, which are based on user selections among benefits and risks, are mapped to allow for targeted planning efforts to prioritize tree planting or tree protection to improve forest and human health and sustainability.
i-Tree Landscape is geared toward planners and managers working at the landscape scale (city, county, regional, state, national forest) to aid them in understanding their local forest resources and risks to forest and human populations, prioritizing management locations and developing land management plans.
i-Tree Landscape is an evolving tool with additional layers and features added annually.
New map information in development includes:
- additional geographic boundaries to aid in comparisons and prioritization (e.g., federal lands, 90 m resolution pixels)
- new tree benefits (e.g., tree effects on air temperatures and human health, water quality effects)
- new risks to humans and trees (e.g., brownfields, flood and riparian zones, forest fragmentation, impaired waterways, potential hurricane threats, projected development, threatened and endangered species, threats to water quality, tree species shifts due to climate change
As this program is relatively new, the planning community is invited to send feedback on how to improve the utility of the program for urban and rural planners.
Nowak, D.J., and E.J. Greenfield. 2018. "US Urban Forest Statistics, Values, and Projections." Journal of Forestry 116(2):164–177. https://doi.org/10.1093/jofore/fvx004.
Top image: Photo by Victor Hanacek, picjumbo.com.
ABOUT THE AUTHOR
David J. Nowak, PhD
is a senior scientist and team leader with the USDA Forest Service, Northern Research Station in Syracuse, New York. His research investigates urban forest structure, health, and change, and its effect on human health and environmental quality. Nowak has authored over 300 publications and leads teams developing the i-Tree software suite that quantifies the benefits and values from vegetation.