Every year the conservation organization American Forests publishes its National Register of Champion Trees. The National Register was first established in 1940 and documents the largest living tree of each species in the United States. In 2020 Florida took home 92 championships, making it the state with the most Champion Trees in the county. Suffice to say Florida loves its trees. Therefore, it comes as no surprise that FDOT is committed to treating Florida’s trees as the assets they are. As with earlier research done on the monarch butterfly, FDOT’s Office of Maintenance sees several benefits from responsibly managing roadside environments. Trees provide a pleasing aesthetic, prevent erosion to maintain roadway integrity, absorb carbon dioxide, limit solar heat absorption, and can reduce driver speed to encourage safer driving. Based on a March 2014 study, environmental benefits like these produce at least a half billion dollars in benefits to Floridians.
FDOT’s Bold Initiative invests $40 million annually on managing vegetation, which has made FDOT the largest planters of trees in the state. To maximize the benefits of its plantings and use those funds most effectively, FDOT initiated a research project to better integrate horticulture practices into its routine maintenance. FDOT’s Jon Heller in the Office of Maintenance served as the Project Manager for the research. Dr. Andrew Koeser at the University of Florida led a team to identify best arboreal practices and update FDOT guidance for maintenance of trees planted on roadsides.
Like the trees themselves, FDOT expects the research investment to grow over time. Dr. Koeser, who served as the Principal Investigator for the research project, says, “If they’re cared for, trees appreciate in value beyond what was invested initially. That is why this research is important, because we are trying to get the full value and potential out of these trees for decades to come.”
Planting the Seeds for Success
FDOT is a major planter of trees in the state, and it is not an easy job. The most tenuous time in the tree’s life is typically when they are transplanted, regardless of environmental circumstances. When introduced to a roadside environment, tree health may be challenged by many factors, such as less fertile soil conditions, roadway runoff, and pollution. Planting palm trees adds complications for maintenance staff, as palms differ significantly from other trees. Most notably, palms are not comprised of wood or bark and have different watering needs.
The research team set out to solve these problems so palms and other trees can thrive when they are transplanted. The team conducted a statistical analysis of twenty-one planting projects across seven FDOT districts. They collected data on site characteristics, soil conditions, and care practices. Care practices generally included watering, mulching, and staking.
The research team further classified and analyzed trees by type, recognizing that different tree types have varying needs to be successfully transplanted. Tree types included shade trees, small-stature trees, conifers, and palms. The research team made distinctions between shade and small-stature trees. Shade trees include species that grow to at least 30 feet when mature, while small-stature trees do not.
Source: Project training materials
The research team also conducted a literature review to better understand the different needs for palms in the context of FDOT’s current tree and palm maintenance guide. FDOT had laid the groundwork to better manage trees and vegetation. Now it was time to see their findings grow.
Maintenance Practices Bloom and Grow
After collecting data from planting sites across the state, the research team identified some important findings. First, the tree plantings were largely successful with an establishment rate of 98.5%. This is largely attributed to the tree species that FDOT selects, which are naturally more resilient. The research team found species selection is particularly important. For example, the species Pinus elliottii (slash pine) outperformed the species P. palustris (longleaf pine) and Taxodium distichum (bald cypress).
The addition of irrigation was also linked to better predictors of long-term health. Palm trees, in particular, were found to benefit from an irrigation system. While the majority of trees were healthy and established, the research team did note that mowing damage could be avoided through a combination of mulching, staking, and increasing planting density.
Lastly, the research helped FDOT understand that trees can often recover if they are on the decline. Prior to conducting the research, FDOT had been replacing any trees that were not graded favorably based on Florida’s Nursery Grade Standards. Through the research, FDOT found that distressed or damaged trees could recover over a period of six to eight months with proper care. Rather than continuing to replace trees, FDOT used this finding to identify remediation measures and give the trees more time to recover.
The research team also developed an efficient, peer-reviewed methodology to assess the health of palms. This is especially helpful for FDOT inspections, as it gives personnel some key indicators to look for in the field like canopy size and color. The project team further implemented this research by updating FDOT’s A Guide for Tree and Palm Maintenance Along Florida Roadsides to provide all the pruning basics for staff and contractors. This also included a contract specifications guide, covering 34 common pruning scenarios.
Source: Project training materials
Finally, the research team conducted five in-person technology transfer events with FDOT staff to share the research findings and improved practices. FDOT Project Manager Jon Heller says, “We pulled together both our asset maintenance groups and DOT personnel for all-day trainings. We went over the science of palms and trees, proper trimming techniques, and how to rate trees – if they were healthy or starting to decline. We wanted to see if they got their correct training out of these sessions, so we gave them a pre- and post-test, and we saw that they did.”
Thanks to the research team, FDOT staff are now equipped with important information on how to manage roadside trees. In time, the staff who learned tree maintenance from the researchers will train other staff in their groups. Given time and FDOT’s continued care, there may be more Champion Trees in Florida’s future.
Further Reading
BDV31-977-75 Clear Recovery Zone Vegetation Requirements, and Review of Current Tree Pruning and Maintenance Practices for Landscape, Urban and Rural Areas within the Right of Way
Final Report | Summary
Florida Department of Transportation Research Showcase 