Summary Rooted-cuttings and saplings of green ash (Fraxinus lanceolata) and hybrid poplar (Populus spp) were planted on a former municipal refuse landfill and on a nearby nonlandfill control plot. The root systems of four trees of each species and size were excavated on the landfill plot -two growing in an area where the concentrations of anaerobic landfill gases were relatively high and two in a relatively low-gas area. Two trees of each species and size were also excavated on the control. The root systems of both species were significantly shallower on the landfill plot than on the control. Green ash appeared to avoid the adverse gas environment of the deeper soil layers on the landfill by producing adventitious roots. Hybrid poplar became adapted in a different manner, by redirecting root growth from the deepter soil layers to the soil surface.

Gleditsia triacanthos var. inermis seedlings were field planted in compacted and non-compacted soil in both normal oxygen and reduced oxygen soil atmosphere. Entire root systems were excavated and mapped. Compaction caused significantly shallower roots in normal and reduced oxygen areas. Roots in the reduced oxygen area were not significantly shallower than in normal oxygen areas. Root spread was correlated with stem diameter and branch spread. Lateral roots extended three times as far from the trunk as did the branches.

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