The Parking Forest is an assembly of materials to incorporate trees and stormwater management into parking lots without losing parking spaces. This presentation was presented by Todd Prager of Prager & Associates and is posted with his permission.

1. How Much Soil Does a
Parking Lot Tree Need?
Contact:
Todd Prager, AICP, ISA Certified Arborist
Phone | 971.295.4835
Email | todd@toddprager.com

2. Trees Need Soil to Grow
Graph Source: USDA Forest Service Center for Urban Forest Research

3. Soil Volume & Crown Diameter
10 ft Crown
100 cu ft Soil
21 ft Crown
500 cu ft Soil
Source: Casey Trees
30 ft Crown
1,000 cu ft Soil

4. Soil Volume & Crown Diameter
20 ft Crown
450 cu ft Soil
5 ft Crown
40 cu ft Soil
40 ft Crown
2000+ cu ft Soil
Source: Real World, Tigard

5. Soil Volume & Crown Diameter
Source: Real World, Tigard

6. Tree Roots Don’t Generally Grow Under Pavement
http://www.flaroccaandsons.com/images/COM/lg/60,000-sf-Parking-Lot-Paving-4.gif
Pavement Profile
AC surface
Aggregate base
Subgrade
Compaction requirements
(90%-95% Proctor Density)
are root limiting

7. Tree Roots Don’t Generally Grow Under Pavement
Graph Source: Up by Roots, James Urban

8. When Tree Roots Grow “Out of the Box”
AC surface
Aggregate base
Subgrade
Roots growing in base layer
lifting curb and asphalt

9. Options for Tree Roots Under Pavement

10. Options for Tree Roots Under Pavement

11. Options for Tree Roots Under Pavement
Structural Soil
Source: Deep Root– Silva Cell - http://www.deeproot.com

12. Options for Tree Roots Under Pavement
Structural Soil
Source: Cornell University – CU Structural Soil - http://www.hort.cornell.edu

13. Options for Tree Roots Under Pavement
Comparison after 10 years of growth
Olympia, WA
Control Trees
Trees with
Structural
Tree Soil

14. Canopy Deficient Commercial/Industrial Zones
Branching Out:
Urban Forest Planning

15. Canopy Deficient Commercial/Industrial Zones
Branching Out:
Urban Forest Planning

16. Canopy Deficient Commercial/Industrial Zones
Branching Out:
Urban Forest Planning

17. Parking Lot Greening
Existing Citywide Canopy (2007) – 25%
Citywide Canopy Goal (2047) – 40%

18. Parking Lot Greening
30% Canopy
Min. Per Parking Lot
&
1000 cu ft Soil Volume
Min. Per Tree
Branching Out:
Urban Forest Planning

19. Soil Volume Strategies

20. Soil Volume Strategies

21. Soil Volume Strategies

22. Questions?
Contact:
Todd Prager, AICP, ISA Certified Arborist
Phone | 971.295.4835
Email | todd@toddprager.com