Patterns of Structural Failure in Monterey Pine

The California Tree Failure Report Program database was established in 1987 to collect data on tree branch, trunk, and root breakage or uprooting. The database for the CTFRP is compiled from failure evaluation reports filled out by statewide cooperating arborists, tree assessors, and other horticultural professionals. Compilation of 186 reports for Monterey pine (Pinus radiata) has permitted development of a "failure profile" -a characterization of failure location, structural defects, decay, climatic conditions, and other factors associated with structural failure of Monterey pine. Monterey pine was found to be particularly failure prone compared to other tree species in Golden Gate Park, San Francisco, CA. Close to 60% of Monterey pine failures reported in the CTFRP database were limb failures, rather than trunk or root failures, and most of these were considered to be heavy lateral limbs - a structural defect. The majority of limb breakage occurred away from, rather than at the point of attachment, suggesting a wood strength problem. Decay was notfrequently associated with Monterey pine failures at any location on the tree. Tree spacing, nutrition, and genetic strain are likely to be major factors influencing heavy lateral limb development. Closer tree spacing, low nitrogen input, and genetic selection offer hope for reducing Monterey pine branch failure.