The intimate interaction of clay with the organic matter is what allows life to thrive. Only inputs of organic amendments can maintain soil structure. A soil with good structure can be walked on. The aggregates of clay micelles retain their form despite the additional forces. Soil structure allows for the passage of oxygen from the atmosphere to the organisms in the soil, and for the atmospheric release of carbon dioxide.
Soil structures act like lungs, providing a range of pore sizes for the gas exchange to take place.
Mulch, in its initial stages of decomposition, protects the soil by redistributing the weight of pedestrians over an area larger than the pedestrian's foot. As the mulch decomposes further, it builds structure as well. According to Lanky Morill, administrative assistant III with the Department of Parks and Recreation, when too much water is present, mulch helps to cushion the weight of any traffic, and that it also helps to speed evaporation by wicking water up to the surface. In dryer conditions, mulch also facilitates condensation, increasing the moisture level in the soil. According to Kobayashi, before the campus had pavements, the problem of removing mud from shoes was solved by having sticks available at intervals that coincided with the maximum amount of mud that shoes collected.