City of Irvine
2020 Local Hazard Mitigation Plan
tree mortality. For instance, a strong earthquake could result in the failure of several dams, reservoirs, or levees in the area. The sudden inundation with floodwaters that would result could kill several trees in the City.
Table 3-7: Pandemic Influenza Phases 42
Phase
Description
Phase 1
No animal influenza virus is known to have caused infection in people.
Phase 2
An animal influenza virus has caused infection in people. There is a potential pandemic threat.
An animal influenza virus has caused occasional infections or infections in small groups. There may be limited human-to-human transmission, but nothing large enough to sustain community-level outbreaks. Human-to-human transmission can sustain community-level outbreaks. There is a significantly higher risk of a pandemic. Human-to-human transmission in at least two countries in the same region. A pandemic is likely imminent. Human-to-human transmission in at least two countries in the same region and in at least one other country outside of the region. A pandemic is underway. Transmission levels are declining below peak levels, although second waves may occur, and transmission could return to previous levels or higher.
Phase 3
Phase 4
Phase 5
Phase 6
Post-peak
Post-pandemic
Transmission levels have returned to normal levels for seasonal influenza outbreaks.
There is no universally accepted scale for measuring tree mortality, but the U.S. Forest Service identifies a general model that compares the aggregate number of tree deaths in relation to the aggregate number of trees surviving over a specified period. 43 Additionally, a meta-analysis of tree mortality studies reveals that most trees in urban forests have an average lifespan lasting between 19 to 28 years and that the mortality rate among these trees is 3.5% to 5.1% per year. 44 If tree mortality rates occur at a rate that is higher than this or if newly planted specimens are dying before 19 years, it could indicate that the City’s trees are being afflicted by disease, pests, or some other issue. The City is also following the University of California Integrated Pest Management guidelines for shot hole boring pests. Table 3-8 identifies the damage rating based on invasive pest quantity.
Table 3-8: UC Integrated Pest Management Guidelines for Shot Hole Boring Pests
Damage
Invasive Pest Quantity
Minor
Under 25 Hits Under 75 Hits
Moderate
High
76+ Hits
Past Events
Agricultural Pests Irvine has had a long history of agricultural use within the community. However, since incorporation as a City, agricultural uses have been replaced with development. This reduction in agricultural use has reduced the amount of agricultural resources affected by pests. Currently the City is partially located within the quarantine area of the Asian Citrus Psyllid, which main affects citrus trees. However, the City does not track and monitor the impacts of this pest on these resources currently.
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