Patterns of Structural Failures in Urban Trees: Coast Live Oak (Quercus agrifolia)

"Data from the California Tree Failure Report Program (CTFRP) were analyzed to develop a profile of the structural failure characteristics for coast live oak (Quercus agrifolia). The most common pattern of structural failure for coast live oak reported in the CTFRP is a root or low trunk failure of a naturally occurring tree growing in a residential site. Decay, site grade changes, and low wind speeds are significantly more frequently associated with coast live oak failures than with other hardwoods, conifers, or eucalyptus. Decay of roots and lower trunk was a major contributing factor to failure of coast live oak (83%). Saturated soil conditions associated with root failure were also more frequent for coast live oak than for other species groups. Careful attention to controlling excess soil moisture, avoiding or correcting grade change and compaction, and monitoring decay are essential to maintain the health of coast live oak."