Being optimistic is one thing, but expecting trees that grow to over 20 feet wide and 200 feet in height to be happy in planting strip 20 feet across borders on being delusional.

We recently received samples from a giant sequoia and a Western red-cedar, both of which grow to marvelous, majestic trees in their native habitat, wedged into a narrow bit of soil that was surrounded by acres of hard pavement (see aerial view below). This type of environment is extremely harsh, and is somewhat equivalent to us living in and never moving from a sky-lighted closet three feet on a side. For our entire lives.

Plants require soils that allow their roots to exchange oxygen with the soil, soils in which their roots can expand and grow, and that have adequate moisture retention capability. Trees surrounded by paving have limitations to all these necessary conditions. Add in the additional burdens of reflected summer heat from the surrounding hard surfaces, which can be 20-45 °F hotter than shaded pavement (Akbari, et al.), and limited (if any) irrigation, and stress on the trees is compounded. Trees that grew well when young will begin to slow their growth. If conditions do not improve, over time, especially as the trees increase in size, they will begin to show stress by dropping needles from the inside out and showing poor color (some of the affected trees are indicated by the arrows). Stressed trees are more susceptible to invasion by beetles that bore under the bark, further weakening the trees and hastening their decline.

This sad scenario can be avoided by developers installing smaller, drought- and heat-tolerant trees. Better yet, there are some very creative ideas regarding improving this situation to begin with by using cooling pavement materials, permeable pavements, bioswales that can catch and cache water, and harvesting the heat from pavements to reduce the surface temperatures.

Reference

Akbari, H., D. Kurn, et al. 1997. Peak power and cooling energy savings of shade trees. Energy and Buildings 25:139–148. (EPA Heat Islands site: http://www.epa.gov/hiri/mitigation/trees.htm)