In Maryland, all new development is now required to put utilities underground, thus avoiding above-ground conflict with growing trees. Each of these achievements provide components of a strong future model for healthy urban forests. Engineering the underground space Sound urban forest planning like that in Portland or Milwaukee requires not only above-ground locations for trees, but serious consideration of underground matters. Competition for underground space is one concern, especially in dense urban centers where underground utilities are taking increasingly large amounts of room. But another major issue has to do with the soil.
Most urban soils are no longer suitable for adequate root growth.
As larger buildings, wider roads and larger and more powerful construction equipment press down on soil surfaces, the overall result is massive soil compaction. Soil Scientist Jim Patterson cites some startling facts. In Washington, DC, he has found that the soils on the Mall stretching between the Capital building and the Washington Monument are so compacted that the average soil density is comparable to a cinder block. Pore space is the ratio of soil particles to voids where air and water can be found. While the ideal pore space for growing trees is about 50 percent, the average pore space on the Mall is often less than 35 percent and sometimes drops as low as 13 percent.