Return to Table of Contents – Summer 2010 TREE Fund Report
Period covered: September 2009 – May 2010
Summary of activities The project is progressing as expected. In the summer of 2009, an undergraduate began breaking small trees (white pines and red maples, approximately 4-5” dbh) with and without defects in the laboratory. That work continued this spring. In the summer of 2010, the field team will perform more tree breaking tests on larger trees (approximately 10-20” dbh) in the field. The graduate student in civil engineering began developing a finite element model of large shade trees based on previously collected data. The finite element model is basically a computer simulation of tree movement and stresses in the wind. If it fits the data collected in the field (as so far it has), it can be used to predict stresses in the tree when decay is present.
Measurements of tree strength from the breaking experiments (in the lab and in the field) are being made for trees with and without defects (both naturally-occurring decay and defects simulated by drilling or carving out sound wood from the trunk). These measurements will help calibrate the finite element model to see how closely the computer model can predict what was measured on real trees. Current work on the finite element, based on previously collected empirical data, indicates that the computer model could be reasonably accurate. This complex tool, however, will need more field data to help improve its predictive ability.
Collecting those field data (and in the lab), however, also produces some immediately useful information about the breaking strength of trees (large and small, with and without defects). Knowing the breaking strength of trees with and without defects will help arborists and urban foresters in assessing the likelihood of tree failure. Knowing the modulus of elasticity (or stiffness) of trees will help refine more advanced models of tree risk assessment, such as the pull test.