The goal of good street tree maintenance and management is to maintain all the many ecological, social and climate benefits of having trees in our city while minimizing risks to “targets”, i.e., people and property. Trees in the public right of way, our “street trees” and trees in the landscaped median islands, are growing in a space with many and frequent targets that make their management and pruning particularly important, as public safety is of primary concern. But it’s very important to prune trees correctly, as poor pruning can damage a tree irreparably.
At this week’s Lunch and Learn we had a special guest, Tim Tyson, the City’s Chief Forester and head of the Urban Forestry Division at StreetsLA. Tim has 45 years of experience in the field, including 25 years with the City. He shared with us the most important things to consider for proper and effective tree pruning of street trees.
First, before beginning to cut, the tree surgeons need to look for site conditions and potential conflicts, such as energized overhead wires, signage and buildings. Then they consider the tree species, as its growth rate, form and other characteristics, determine how it responds to different kinds of pruning cuts and decisions. The City of Los Angeles follows the Tree Pruning Guidelines from the International Society of Arboriculture (ISA) for tree maintenance activities. As part of regular pruning, the City has to achieve certain clearances, that is the amount of space between the street or sidewalk, and the lowest branches of the tree.
Also, staff training and qualifications are very important. In the Urban Forestry Division, there are 35 Certified Arborists, including nearly all of the Tree Surgeon Supervisors. Because of the expertise on staff, as well as recent staffing additions, the City of Los Angeles now completes all tree maintenance activities in-house, using highly trained City staff members instead of contractors. This allows the City to strictly control the quality of the pruning that happens. Last Fiscal year, using City staff only, we were able to successfully prune over 37,000 trees around Los Angeles.
Improvements in staffing levels have played a key role in improving the pruning of our street trees, and Tim identified that the Urban Forestry Division’s work in the future will be informed and guided by our inventory data, allowing for further improvements and potential efficiencies.