Managing Trees at the San Francisco Botanical Garden with GIS

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 that made up the western part of the city. 

Located within the park is the San Francisco Botanical Garden at Strybing Arboretum. The garden is a 55-acre horticultural refuge where plant collections from other parts of the world, such as Chile and Australia, are cared for under the impressive canopy of pine, cypress, and gum trees. 

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, which 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 in Stamford, Connecticut, with research laboratories in Charlotte, North Carolina, was 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 knew that hundreds of person-hours of work would be needed to complete all the required tree pruning, support system installation, and removals. 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-based tree maintenance inventories. Its 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 4.5 feet above ground level or any tree that showed visual evidence that it may fail. Using ArborVue, arboriculturally focused GIS software built with Esri’s ArcPad and ArcGIS Engine, not only would tree attribute information be recorded (e.g., tree species, diameter, health), but recommendations for improving tree stand health and structure (e.g., pruning, structural support system installation, or tree removal) would also be included. Furthermore, the recommendations would be prioritized using a visual risk rating system 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/International Society of Arboriculture (ISA)-certified arborists from Bartlett’s laboratories teamed up with the local Bartlett representative and a consultant from HortScience, a horticultural consulting firm based in Pleasanton, California, to form the two inventory teams that would complete the job. Using ArcGIS, the GIS specialists overlaid a CAD drawing of the garden on digital content obtained from GlobeXplorer Inc., an Esri partner. 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 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, the teams captured attributes for 710 trees in the inventory. Although the majority of the trees were Monterey pine (Pinus radiata), Monterey cypress (Cupressus macrocarpa), and blue gum (Eucalyptus globulus), the teams recorded a total of 132 different tree species. 

The goal of the inventory was to recommend removal of hazardous trees and make recommendations for maintaining the safety, health, and structure of the mature tree canopy. It was determined that 140 trees (19 percent) needed to be removed because they posed potential hazards or were in advanced stages of decline. In addition, 513 trees (73 percent) needed to be pruned for safety, health, structure, or appearance. Another 47 trees (6 percent) needed tree support systems installed or inspected to reduce branch and crown failure potential. To assess sound wood strength, 33 trees (4 percent) required further quantitative tree structure evaluation. Tree diseases such as pine pitch canker, pests such as 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 together and prioritized. The GIS specialists generated maps to illustrate where trees were located, along with the associated recommendations. Further queries were developed and illustrated on maps to show daily work and progress. As with most large organizations, there were numerous other projects going on at the same time as the tree work. Using GIS developed for the garden, tree work projects could be reprioritized around other projects taking place. 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 the San Francisco Botanical Garden have had the recommended work completed. Thirty trees, from 15-foot stumps to 200-foot trees, have been removed, and 150 trees have been pruned or had structural support systems installed. A total of $452,500 had been donated and has been invested in the garden, including the tree inventory/management plan, all 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 region were felled or badly damaged. Throughout the 55-acre San Francisco Botanical Garden, only five trees were lost or damaged, and these trees were in low-priority areas of the garden. Garden officials credit the work prescribed and carried out through the GIS model of the management plan as the reason there was so little damage to the garden compared to the rest of Golden Gate Park. 

For more information, contact Patrick Anderson, GIS support specialist, Bartlett Tree Research Laboratories (e-mail: panderson; tel.: 704-588-1150, ext. 127). 

From ESRI Forestry GIS Journal, Spring 2011
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