This is a typical problem in a Park landscape. Hardsurfaces require a stable base material, generally gravel, here it is 3/4 minus with larger rock beneath to support the occassional/routine use by Park’s vehicles. This base extends out from the hard surface on a relatively wide angle. The soil below it is compacted before the gravel/rock is installed. The surface to the right is an experimental porous concrete mix to minimize runoff. This requires the base rock as well to help contain the water that percs through. It may require even more base support as this porous mix has less structrual strength than ‘normal’ concrete. These two Gingko trees are planted in a space that is roughly 24″ wide but is effectively much narrower because of the base compaction and rock. These trees have two strikes against them.