Impact of Planting Depth on Fraxinus pennsylvanica ‘Patmore’ Growth, Stability, and Root System Morphology

Abstract

Trees are often deeply planted as a result of nursery and landscape practices. While past research has investigated the impact of deep planting on tree growth and survival, its impact on whole-tree stability is not well documented. Green ash (Fraxinus pennsylvanica ‘Patmore’) trees were planted at three different depths in research plots and established for nine years. In assessing aboveground growth, planting depth had no effect on stem diameter growth (measured as dbh) (P = 0.421; n = 32) or tree height (P = 0.501; n = 32). Static pull tests were conducted to evaluate the consequences of deep planting on tree stability. Using structure from motion (SfM) photogrammetry-derived computer models to assess root architecture, we found the most significant factors affecting tree stability were: 1) root volumes in the top 10 cm of the soil in a 90° wedge on the side opposite of the pull direction; 2) root volumes 40.1 to 50 cm deep in a 90° wedge on the side opposite of the pull direction; and 3) root volumes deeper than 60.1 cm deep in a 90° wedge on the side opposite of the pull direction (final model: P < 0.001; n = 30; adjusted R2 = 0.852). The importance of structural root morphology throughout the soil profile and implications for urban root-soil relations on tree stability are discussed.