Table 2.

Regression analysis was used to determine the relationship between root depth and tree performance, with depth as the independent variable and crown vigor or trunk diameter (only on sites where trees of uniform size from the same source were all planted at the same time) as the dependent variable. Logistic regression was used for crown vigor and trunk condition ratings. Linear regression was used for trunk diameter measurements. Where insufficient trees were available for some species, data is reported by genus.

Genus/speciesCrown vigorTrunk diameterTrunk condition
Greensboro, NC – July 2008
Acer rubrum0.3060.0500.0420.1530.3060.017
Snoqualmie, WA – November 2007
Quercus rubra0.0050.7120.0200.326----
Tilia cordata−0.0480.9360.0810.045----
Fraxinus oxycarpa0.1070.5590.1300.010----
Glen Ellyn, IL – June/July 2007
Fraxinus sp.z0.2290.231--------
Quercus bicolor0.4810.002--------
Quercus sp.0.2020.166--------
Ulmus hybridy0.0810.763--------
Tilia cordata0.5710.118--------
Gleditsia triacanthos0.1530.386--------
Acer × freemanii0.2290.428--------
Taxodium distichum0.4290.478--------
Gymnocladus dioica0.5560.096--------
  • zF. pennsylvanica and F. americana cultivars are usually grafted on F pennsylvanica root stock.

  • yHybrid elm cultivars are usually grafted on Ulmus pumila root stock.