Roughly 80 percent of urban tree health problems originate from conditions below ground. A tree is supported both structurally and nutritionally by its roots -- any limitations placed on its roots will result, directly or indirectly, in future health problems. These resources explore the fundamental relationship between soils and roots, and how to grow trees to create the best growing conditions below ground.
Providing uncompacted soil volume for tree growth
Soil volume and tree growth are directly related. Several techniques exist to protect soil volume under pavement from compaction so the soil can support root and tree growth. These methods can also be used in biorentention practices that treat stormwater runoff.
Design
Tree Space Design is a publication that explores the relationship between soil volume and tree growth and provides strategies to grow trees 'out of the box'.
Engineered Rock Based Soil
Cornell Urban Horticulture Institute offers a variety of resources on Cornell's (CU) Structural Soil. This is a patented formula available only through licensed producers. Other types include Stalite, Swedish and University of California (UC) Davis' structural soil.
Structural Cells or Suspended Pavement
The costs to install these systems are much greater than simply putting a tree in a 4 x 4 foot cut out, but the outcomes are much better. The trees have access to uncompacted soil volume, allowing them to thrive and grow to a size yielding maximum ecosystem benefits. If we consider trees as green infrastructure and as sources of necessary services like clean air and water, the trees will pay the costs of these systems back quickly.