Average depth (mm) and range in depth (in parentheses) of sycamore roots (roots > 5 mm [0.3 in] diameter) in the top 30 cm (12 in) of soil adjacent to sidewalks with various root barriers in two soil types.
| Treatment | Well-drained soil | Poorly drained soil |
|---|---|---|
| No sidewalk/no barrier | 76 c* (25–170) | 72 d (13–195) |
| Sidewalk/no barrier | 101 b (33–180) | 122 b (55–248) |
| Sidewalk/Biobarrier® | 107 b (20–245) | 138 a (65–275) |
| Sidewalk/Deep Root | 117 b (35–235) | 105 c (50–223) |
| Sidewalk/gravel sub-base | 194 a (109–306) | 131 ab (0–230) |
| Sidewalk/polyethylene | 108 b (37–223) | 131 ab (65–235) |
| Statistical significance | ||
| Treatments | P < 0.0001 | |
| Soil type | ns | |
| Treatments × soil type | P < 0.0001 | |
↵* Means in a column with a different letter indicate a significant difference at P < 0.05 with Duncan’s MRT. Means were calculated by averaging the distance between the root and soil surface of all roots encountered at the edge of the walk. Note: All treatments had a 1.2 m (4 ft) wide sidewalk installed 0.6 m (2 ft) away except where indicated. Barriers were on same side of the sidewalk as the tree; root excavations were done at the edge of the other side of the walk.