The number of species that can tolerate poor-quality of roadside soils is limited. Can we increase the diversity of trees that can thrive in this harsh environment and the ecosystem services provided by urban trees by matching soil amendments with tree traits?
The Illinois Tollway is undertaking a three-year initiative to plant 58,000 trees along their 292 mile right-of-way to increase the regional forest canopy in the Chicagoland area. Soils in the sites available for this project are likely of poor quality: compacted, nutrient-poor, and saline due to topsoil removal, grading, and compaction that occurred during Tollway construction and pollution by de-icing salts. Two broad strategies are commonly used to maximize tree survival and health in such an extreme environment: 1) extensive soil preparation to mimic natural forest soil – that is, with horizons, higher porosity and aggregation, and increased organic matter, and 2) choosing the “right tree” for the “right site” – that is, selecting tree species that are salt-, pollution-, and drought-tolerant. However, the Tollway seeks to not only increase the number of trees, but also the diversity of trees in the region. Furthermore, there is not one “forest soil,” but rather many types of forest soils than vary with tree community composition. Here, we propose a new paradigm and research project to evaluate whether organic matter amendments that best match the chemical properties of a tree species’ natural environment maximize tree growth and survival as well as soil ecosystem functioning. That is, can we enhance the diversity of tree species that can persist in a roadside environment by moving from “right tree, right site” to “right amendment, right tree”? This project has the potential to set the standard for tree planting site soil preparation. Documenting the benefit of this could establish the value of proper site preparation and help to establish it as the standard for roadside plantings and all landscape plantings.
The Illinois Tollway, The Morton Arboretum