A Tale of Two Trees
In February 2011, two different tree pits were planted at the same time with the same tree species (Chinese Elm) at the Ashfield Civic Centre in Sydney, Australia. The tree in the centre forecourt was planted using the Stratacell™ suspended pavement system while the two trees near the sidewalk were planted in structural soil (rock/soil matrix).
Over a year later, the canopy density of the tree planted using the Stratacell system (suspended pavement – middle and far left images) is significantly thicker than the one on structural soil (rock/soil – shown on far right).
These early results from the Ashfield project are well supported by a fascinating study conducted by E. Thomas Smiley, Lisa Calfee, Bruce Fraedrich and Emma Smiley, comparing structural and noncompacted soils for trees surrounded by pavement.
In the 2006 study, Snowgoose cherry and Bosque lacebark elm were planted into five different soil treatment options under pavement, including compacted soil, gravel/soil mixture, Stalite, Stalite/soil mixture, and noncompacted soil.
After 14 months, the study found that there was more trunk diameter growth with the noncompacted treatment than the other treatments. There was also more twig growth, higher relative chlorophyll rating and more root growth compared to all the other systems.
The comparison showed that the foliar rating with the suspended pavement system was significantly better. Aside from this, “the mean SPAD reading of foliar colour was also significantly higher” as well as “the root length at the rhizotrons”.
The study’s conclusions state that “suspended pavement over noncompacted soils provided the greatest amount of tree growth and health and should be considered when designing urban planting sites for trees”.
Citygreen® Stratacell system is an engineered load bearing matrix that supports pavement and traffic load, while providing in excess of 90% uncompacted soil by volume.
Suspended pavement systems, especially those incorporating the soil cell technology, are fast becoming the preferred choice for successful urban tree pit design.
Share with us your experience on trees planted in structural soil and suspended pavement systems.