Managing Trees at the San Francisco Botanical Garden

Golden Gate Park in San Francisco, California was developed in the late 1800s as a recreation area where city dwellers could escape to the outdoors. Throughout the 1,017 acre park, large maturing trees such as Monterey pine, Monterey cypress, and blue gum were planted to secure, what was then, the sand dunes which made up the western part of the city.

Located within the park is the San Francisco Botanical Garden at Strybing Arboretum. The gardens are a 55-acre horticultural refuge where plant collections from parts of the world such as Chile and Australia are cared for under the impressive tree canopy of pines, cypress, and gum. While on a walk through the garden an anonymous donor, who used the garden as her classroom, recognized the potential risks the maturing trees posed to visitors. Many of these giants contained large dead limbs or other structural defects that predisposed the trees to branch, stem or root failure. Coordinating with the San Francisco Botanical Garden Society the donor provided the funding to tackle this large problem.

Bartlett Tree Experts, based out of Stamford, Connecticut and with research laboratories in Charlotte, North Carolina, were called in to help remediate the probability of personal injury due to tree failure at the garden. On their initial tour of the garden, representatives from Bartlett’s San Francisco office knew that hundreds of hours of work would be needed to complete all of the required tree pruning, support system installation, and removals. In order to properly plan, organize and prioritize the work a tree inventory would need to be performed.

One of Bartlett’s many services is conducting GIS (Geographic Information System) based tree maintenance inventories. Bartlett staff worked with garden personnel to define the goals and objectives of an inventory of the Arboretum. The focus of the inventory would be all trees 18 inches and larger in diameter at 4.5ft above ground level, or any tree that showed visual evidence that it may fail. Using ArborVue, arboriculturally focused GIS software, not only would tree attribute information be recorded (i.e. tree species, diameter, health etc.), but recommendations for improving tree stand health and structure (i.e. pruning, structural support system installation or tree removal) would also be included. Furthermore, the recommendations would be prioritized with the help of a visual risk rating system conducted while in the field. Recommendations for further tree evaluation were made for instances where it was difficult to tell from the ground whether a defect in a branch or stem warranted abatement treatment.

GIS Support Specialists/Certified Arborists from Bartlett’s laboratories teamed up with the local Bartlett representative and a consultant from HortScience, a horticultural consulting firm based out of Pleasanton CA, to form the two inventory teams that would complete the job. Using ArcView, a CAD drawing of the garden was overlain on a digital content obtained from GlobeExplorer Inc. Using the newly created map, the garden area was equally divided among the teams of arborists. Each team carried a Trimble Geo 2005 series GPS/data recorder with a Trimble GeoBeacon to capture all of the tree attributes and maintenance recommendations.

The tree inventory was performed during the first week of March 2007, and after a week of exploring the garden’s large trees, data collection was completed. In total, attributes for 710 trees were captured in the inventory. Although the majority of the trees were Monterey pine (Pinus radiata), Monterey cypress (Cupressus macrocarpa), and blue gum (Eucalyptus globulus) a total of 132 different tree species were recorded. 140 trees (19%) needed to be removed because they showed potential hazards or were in advanced stages of decline. The goal of the inventory was not only to recommended hazardous tree removals but to also make recommendations for maintaining the safety, health and structure of the mature tree canopy. 513 (73%) needed to be pruned for safety, health, structure, or appearance. 47 trees (6%) needed tree support systems installed or inspected to reduce branch and crown failure potential. 33 (4%) required further quantitative tree structure evaluation to assess sound wood strength. Tree diseases like pine pitch canker, pests like stem boring beetles, and soil conditions were also recorded during data collection to help manage the trees in the garden.

With field data collection completed, a management plan was developed with work type recommendations grouped and prioritized. Maps were generated to illustrate were trees were located and the associated recommendations. Further queries were developed and illustrated visually on maps to show daily work and progress. As with most large facilities, there were numerous other projects going on at the same time as the tree work. Using the GIS developed for the gardens, trees and work could be reprioritized around other projects taking place on the gardens. Additionally, Garden Staff made all tree inventory information and maps available to the general public and 30-day removal notices were posted to diffuse any public concern.

To date, most of the high priority trees and areas of San Francisco Botanical Gardens have had the recommended work completed. Thirty trees, from fifteen foot stumps to 200 foot trees, have been removed and one-hundred fifty trees have been pruned or had structural support systems installed. Thanks to a very concerned donor, a total of $452,500 has been invested in the gardens including the tree inventory/ management plan, all of the work associated with the pruning and removals and the tree succession planting plan. It is worth mentioning that not long after high priority tree pruning and removals were completed, a severe storm hit the city. Many trees in the Bay area were felled or badly damaged. Throughout the fifty-five acres of the San Francisco Botanical Garden only 5 trees were lost or damaged, and these trees were in low priority areas of the gardens. Garden officials credit the work prescribed and carried out through the GIS model of the management plan as the reason why there was so little damage to the garden compared to the rest of Golden Gate Park.

As seen in ArcNews, Winter 2008/2009.

For more information, contact:

Tina McNulty

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