City Trees

otherwise) for this disease. The NPS must diversify the Mall's canopy, but "how do you start changing an iconic monoculture without reducing the cul- tural significance of the landscape?" Bassuk asks. That process is detailed later in this article. The twelve overarching recommendations of the Operations and Maintenance Guide are as follows: 1. Have an on-staff arborist or con- tract with a consulting arborist. 2. Use a tree management software system. 3. Develop and fund a budget so that work can be scheduled and completed in a timely manner. 4. Follow a management calendar for timely pest scouting and treatment, planning for tree replace- ment and pruning, and other tree-related tasks. 5. Conduct regular tree risk assessments of the trees on the National Mall. 6. Build tree and soil protection into permits for large-scale events. 7. Consider increasing the tree species diversity on the National Mall. 8. Undertake a robust annual planting effort to replace dead and declining trees. 9. Soil compaction mitigation and mulching should be a regular part of tree main- tenance at the National Mall. 10. Consider prophylactic treatment of the "signa- ture" elms with a fungicide for Dutch elm disease. 11. National Park Service tree care personnel should participate in ongoing technical tree care training. 12. The National Park Service and its sub- contractors should follow industry best practices in all aspects of tree care. Recommendation 7 Resistance: The Way Forward "Consider increasing the tree species diversity on the National Mall"—may seem obvious and basic to city foresters. However, in the case of the National Mall, the goal of landscape sustainability is coming against an attachment to the cultural idea of the American elms. We say "the idea" because in truth, the elm monoculture is not homogeneously healthy and with 3 to 5 trees dying each year, it's not sustainable. Furthermore, in the places where NPS has replanted sites with trees other than straight American elm, visual coherence has, despite best intentions, been disrupted. For instance, the elm cultivar 'Augustine Ascending' is dramatically different in habit than the straight Ulmus americana and draws attention to itself with this upright habit. "It's a beautiful tree, but looks nothing like a straight-species American elm," Bassuk says. The Operations and Maintenance Guide further explains: "It is important to note that the original design intent of having perfectly matched trees with high canopies creating a Gothic arch effect on >> Which one of these is most unlike the others? It's an attractive American elm cultivar, but 'Augustine Ascending' (far left) ascends rather than cascading in a vase shape. Photo by Nina Bassuk 34 CityTREES

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