Soil in a mound will dry out more quickly than surrounding soil. This will be a problem during droughts. Irrigation of mounds is tricky because the water tends to run off the sloped sides. Additionally, the roots of large trees will grow beyond the mound becoming surface root problems in surrounding areas. Compacted soil lacks pore space.
Pore space is needed for the exchange of gases through the roots.
Increasing organic matter in the top foot of soil is necessary for trees and shrubs which have most of their roots in the top 12 inches of soil. Core aeration helps, but amending the soil before planting gives better results. Adding soil over existing roots may result in a plant's death. This is due to reduced gas exchange and changes in drainage. Weather and climatic stresses include high temperature combined with drought conditions and cold, windy conditions.