The higher the bulk density of a soil, the more capable that soil is of sustaining a structure. Bedrock is the most stable surface on which to build, a mucky organic soil would be very unstable. In order to increase the stability of a soil prior to constuction, heavy equipment is run over the surface compacting the soil. This pushes the soil aggregates closer together reducing the size of the macropores. This decrease in porosity so necessary and beneficial for structures is a hindrance to plant growth.
Plant roots have a difficult time extending into soil that has little air space.
This can cause drainage problems if the slope of the soil does not carry the water away as runoff. Although there are a select number of plants that prefer to have their roots wet, in most cases this is unhealthy and can lead to root-rot. If, on the other hand, there is sufficient slope to the soil, the lack of pore space for water to move through means a decrease in infiltration as well percolation. An increase of runoff is the result although its erosive effects are lessened by the increased strength of the soil. The lack of oxygen able to penetrate a compacted layer of soil has its own problems.