1. Urban Design to Accommodate Trees: Parking lot Solutions by Dr. Edward F. Gilman, professor Department of Environmental Horticulture University of Florida, Gainesville http://hort.ufl.edu/woody/planting

2. Outline of topics  Introduction  Site evaluation  Species selection  Formula for success  Roots/hardscape conflicts  Trees/sidewalk solutions  Parking lot/buffer strip solutions  Structural soils

3. Solutions for trees in parking lots and buffer strips The idea is to create a system that can accommodate tree roots while minimizing interference and damage to the infrastructure design and structure edge buffer strips islands interior linear strips Solutions

4. Parking lot construction Parking lots are carved out of existing soil or are developed after soil has been removed or added to the area; in either case, severe soil disturbances almost always occur This makes it tough to grow trees in islands and other small soil spaces constructed in the parking lot design

5. Parking lot design--we can do better Parking lots are typically located between the street and the building with signs placed on the building about 20 feet from the ground This places tree canopies and signs in immediate conflict with each other because they occupy the same vertical space---it is difficult for customers to view signs and the building design

6. Parking lot design--we can do better There are many ways to design parking lots differently, resulting in more sustainable urban areas place signs closer to the ground place signs out by the street and not on the building build the parking lot on the back side of the building install trees with a dominant single trunk and train the lowest branches so they are at least 25 feet off the ground move the trees to the side of the buildings and property borders design

7. Signs and trees sharing the same space When tree canopies grow in the same space as signs, store owners respond by either topping or rounding over the trees, or inappropriately raising the canopy Raising the canopy on single trunked trees results in less maintenance and a longer-lived tree than raising the canopy on the multi- trunked trees pictured here Installing trees with one dominant leader and one trunk in parking lots makes it easier to remove lower branches as they get in the way of the signs design

8. Sustainable parking lot design Trees are located only in the buffer strips surrounding this parking lot--no trees are placed in islands. This keeps lights away from trees and ensures that trees will not have to be pruned to make way for the lights Locating trees in large buffer strips around the parking lot provides roots with adequate space to grow design

9. Most trees in buffer strips-- one large island Trees are located primarily in the buffer strips surrounding this parking lot, not in islands There is only one island (left side) and it is quite large Large parking lot islands and wide buffer strips support large trees design

10. Large island supporting trees and shrubs The parking stalls are located over porous pavers that support grass growth This design allows water and air to enter the soil and should reduce the amount of water running off the parking lot This large island is supporting many trees and shrubs design

11. Non-sustainable buffer strips under wires Trees must be pruned to keep them small This makes for unnecessary work and prevents the urban forest from developing Move this large soil space from under the wires to a different location such as the side of the property as in the next slide Buffer strips at the edge of parking lots are often located under utility wires. THIS DOES NOT WORK! design

12. Sustainable buffer strip on side of property Buffer strips on the side of the property make more sense Often, there are no utility lines on the side of the property Trees in large soil spaces with no utility lines nearby can grow to a large size. design

13. Porous pavers for parking stalls Traditional pavement was used for the travel lanes – cars stalls were constructed of porous paver blocks This should allow for better root growth because air and water is more likely to enter the soil under the porous pavers This parking lot for a large zoo in the southern U.S. was designed to reduce runoff and support good tree growth design

14. Porous pavers near existing trees This parking lot for a large botanical garden was constructed near existing large trees Porous pavers were used to help preserve the root system and soil structure Be sure that the soil grade is not lowered during the construction process because this will damage roots Soil can be added around the roots to prepare a base for the pavers, but be sure it is coarser than the existing soil design

15. Porous pavers near existing trees-detail A close up of the previous photo shows that a large portion of the root system was apparently protected during construction Be sure soil is not removed from the root zone prior to laying the sub-base and the pavers because this would remove a large portion of the root system This photo shows what happens when some of the construction detail was left to chance--note the huge damage to the trunk on the tree in the foreground design

16. Gravel as a parking lot surface Gravel has been used successfully for two decades in this large employee parking lot Trees are very happy and have grown to form a closed canopy If roots grow to the soil surface forming an irregular surface, more gravel is added design

17. Porous asphalt as a parking surface Porous asphalt allows water to run through the surface to a layer of gravel below the surface Forty percent of the volume below the surface is air space that can fill with runoff water This reduces the volume running into adjacent retention ponds and streams design

18. Solutions for trees in parking lots and buffer strips The idea is to create a system that can accommodate tree roots while minimizing interference and damage to the infrastructure design and structure edge buffer strips islands interior linear strips Solutions

19. Buffer strip too narrow to sustain trees Installation of buffer strips around the edge of parking lots are typically mandated by municipal ordinances and codes Narrow buffer strips are fine for shrubs but they are too small to accommodate root growth needed to support trees The large maturing honeylocust trees are likely to struggle; if roots somehow find suitable soil under the walk and pavement, the hardscape is likely to become dislodged and damaged Buffer

20. Buffer strip too narrow-- tree breaks hardscape The original space allocated for the tree roots was much too narrow Roots somehow found suitable soil under the pavement and walk where they grew very well in the 20 to 30 years after planting The trunk flare lifted and disintegrated the curb (see arrow) as roots expanded in diameter Buffer

21. Buffer strip suitable to sustain trees The fifteen foot wide buffer strip at the left edge of this parking lot is more suitable for tree growth than in many designs It will allow for root flare expansion and provide open soil for good root growth for a decade or two One key to success in this design will be preventing compaction by keeping pedestrians off the soil and mulch in the strip Buffer

22. Buffer strip suitable to sustain trees The fifteen foot wide buffer strip between building and street is more suitable for tree growth than many other designs It will allow for root flare expansion and provide open soil for good root growth for a decade or two Roots can share soil in the long strip of open soil space One key to success in this design will be to prevent compaction by keeping pedestrians off the soil and mulch in the strip Buffer

23. Buffer strip suitable to sustain trees for long time The thirty foot wide buffer strip at the edge of the parking lot above is more suitable for tree growth than in most other designs That is the reason why these trees have grown so large Large soil space in buffer strips equates to healthy, vigorous trees Buffer

24. Solutions for trees in parking lots and buffer strips The idea is to create a system that can accommodate tree roots while minimizing interference and damage to the infrastructure design and structure edge buffer strips islands interior linear strips Solutions

25. Large trees are not suited for small islands Planting large-maturing trees in small parking lot islands is not sustainable – something will break Nonetheless we continue to see landscape architects specify large- maturing trees for small parking lot islands Islands

26. Standard planting in a parking lot island Here is a group of standard-issue parking lot islands, each with two red maple trees The space is too small to sustain tree growth for very long Red maple can grow OK in this situation in northern climates but struggles in the South Islands

27. Where are the roots? Occasionally trees can grow in places that seem to defy reason. In the parking lot pictured here trees were able to explore the soil below the pavement and become quite large in relation to the tiny soil space at the base of the trunk This example should not be used as a model for successful design since it is so atypical Islands

28. Big island means healthier trees Here is a parking lot constructed on a compacted clay soil The two trees on the left and center (blue arrows) are larger and darker green than the tree on the right The stressed tree on the right was planted in a tiny island whereas the healthier ones were in a larger island. Islands

29. Small trees for small islands Small-maturing trees such as crape myrtle are the best ones to choose for small islands They cause less damage to hardscape than trees that grow to be large Islands

30. Large tree running out of soil space Large trees planted in small parking lot islands may grow well for 20 years; when they completely fill the soil space with roots, they begin to decline This sawtoothed oak grew here for about 20 years before beginning to show decline as indicated by die-back in the canopy (arrows) Islands

31. Large tree growing well in small space Large trees planted in small parking lot islands constructed over certain soil types can explore the soil beneath the pavement As roots grow and expand in diameter they often begin to lift the curbs and crack the pavement (blue arrows) Islands

32. Large tree cracking curb in small space Large trees planted in small parking lot islands constructed over coarser soil types can explore the soil beneath the pavement As roots grow and expand in diameter they often begin to lift the curbs and crack the pavement Islands

33. Very large tree cracking curb in narrow island The root system on this tree managed to find a way to explore the soil directly under the pavement Two large roots can be seen lifting the pavement (blue arrows); research shows that water and air are abundant on the underside of the pavement surface When a tree manages to get large in a small space, roots typically destroy hardscape Islands

34. Roots lifting curbing in narrow island Trees can grow large in small spaces but the hard surfaces nearby often suffer serious damage There is no way to replace this curbing back to its original location and save the tree Islands

35. Large island with large- maturing oak tree Designing parking lots with large islands such as the one pictured above will allow large-maturing trees to be planted with less risk of them disrupting hardscape Large diameter buttress roots that can raise curbs and walks are farther away from curbs Islands

36. Large islands with large- maturing oak trees Designing parking lots with large islands such as the two pictured here allow large- maturing trees to be planted with less fear of them disrupting hardscape Islands

37. A peninsula can increase available soil space Designing parking lots with peninsulas is a good method of supplying trees with much more root space than the traditional island An island is surrounded on all sides by curbing Recent research shows that the fewer the curbs surrounding the tree the better its growth Islands

38. A peninsula can increase available soil space Trees can grow to be quite large in a peninsula because roots have access to ample soil space Islands

39. Solutions for trees in parking lots and buffer strips The idea is to create a system that can accommodate tree roots while minimizing interference and damage to the infrastructure design and structure edge buffer strips islands interior linear strips Solutions

40. Linear planting strips in a parking lot Trees can grow very well in long planting strips in parking lots Combined with the traditional island at the end of the strip as shown above, this design can lead to many shaded parking spaces. Security lights will conflict (arrow) Linear strips

41. Linear planting strips can conflict with signs Trees in long strips can conflict with building signs if the site is not designed correctly In this design, the security lights (blue arrow) are located away from the tree planting strips; this eliminates conflicts between lights and trees and reduces maintenance Linear strips See next slide for alternatives

42. Alternatives to tradition move the trees to the edge and sides of the property select and train trees to a single leader to ease canopy raising reduce sign height move the signs to the front edge of the property move the building toward the street and place trees behind building Linear strips

43. Linear planting strips supporting trees These trees in a long, fairly wide planting strip are growing well The close spacing between trees allowed the canopy to close quickly over the parking spaces Linear strips

44. Long strips support healthy trees These three trees in a long planting strip are growing well The shrubs and ground cover planted in the strip help keep people off the soil, thereby preventing soil compaction Compacted soil can dramatically reduce tree growth Linear strips

45. Trees are growing into lights These trees are growing nicely due to good site design; long linear strips allow roots to share soil space However, since the security lights were installed way too high (blue arrows) the tree canopy is beginning to reach the lights This conflict often leads to poor tree pruning choices resulting in unhealthy trees Linear strips

46. Trees healthy due to lots of soil space These trees are growing nicely due to good site design Long linear strips allow roots to share soil space Linear strips

47. Success from long linear soil strip Long wide strips are better able to support trees than small islands Here is a very successful project using clonal trees that created a nice border and screen Linear strips

48. Wider is better Very wide soil strips in parking lots allow for optimal tree growth This strip is forty feet across and will support trees for decades Linear strips

49. Wide strip supporting a double tree row Very wide soil strips in parking lots provide the best trees This strip is fifty feet across and has supported this double row of oaks for decades This is sustainable urban design Linear strips

50. Root barriers can deflect roots Barriers have been placed vertically in the soil to deflect roots away from hardscapes Place the barriers sufficiently away from the structure (about six inches) to be protected so that as the roots grow wider they will not touch the curb or walk Be sure the top of the barriers reaches above the top of the soil so roots do not grow over it Solutions

51. Root barriers can deflect roots Roots are deflected horizontally and down by most of the barriers on the market In compacted soils and soils with a high water table, roots grow under the barrier and up the other side In well drained soil, roots may remain at deeper depths longer Solutions

52. Outline of topics  Introduction  Site evaluation  Species selection  Formula for success  Roots/hardscape conflicts  Trees/sidewalk solutions  Parking lot/buffer strip solutions  Structural soils

53. Many tools at your disposal Other professionals – engineers, planners, architects, landscape architects, urban foresters, arborists Species selection and spacing Creative design solutions Ordinance and code changes

54. Root barriers can deflect roots Barriers have been placed vertically in the soil to deflect roots away from hardscapes Place the barriers sufficiently away from the structure (about six inches) to be protected so that as the roots grow wider they will not touch the curb or walk Be sure the top of the barriers reaches above the top of the soil so roots do not grow over it Solutions

55. Root barriers can deflect roots Roots are deflected horizontally and down by most of the barriers on the market In compacted soils and soils with a high water table, roots grow under the barrier and up the other side In well drained soil, roots may remain at deeper depths longer Solutions

56. Outline of topics  Introduction  Site evaluation  Species selection  Formula for success  Roots/hardscape conflicts  Trees/sidewalk solutions  Parking lot/buffer strip solutions  Structural soils

57. Typical root growth under pavement Roots (blue arrow) typically grow directly under the sidewalk slab as shown here because that is where air and moisture is present The sidewalk slab has been remove in the photo Roots lift the walk as they increase in diameter Photo credit: Jason Grabosky, Rutgers University Structural soil

58. Structural soil design Structural soil is designed to support the weight of walks, roads, pedestrians and vehicles as well as provide a well-aerated soil substrate for tree root growth Weight is transferred from aggregate to aggregate then to the soil under the aggregate; no weight is borne by the soil between aggregates. Illustration credit: Jason Grabosky, Rutgers University This allows roots to grow well in the soil between the aggregates Structural soil

59. Structural soil installed Structural soil is composed of small aggregate material (angular rocks about one inch diameter) with enough soil to almost fill the space between the rocks Photo credit: Jason Grabosky, Rutgers University Structural soil

61. Root growth in structural soil after three years Roots grew well in structural soil under a sidewalk (walk has been removed-blue arrow) in the first three years after planting Roots grew down and out from the tree It is not known if all trees will grow like this one Photo credit: Jason Grabosky, Rutgers University Structural soil

66. 9’ 15’

67. Tree growth in structural soil These trees were planted into a strip of structural soil installed in this retrofitted parking lot between the blue arrows They have performed quite well Photo credit: Jason Grabosky, Rutgers University Structural soil

68. Tree growth in clay vs. structural soil Trees on the left were planted in clay soil that was fairly compacted-typical of many job sites; many of these trees were performing poorly as indicated by the die-back (blue arrow) Trees on the right were planted in structural soil installed beneath the sidewalk and they looked great Photo credit: Jason Grabosky, Rutgers University Structural soil

69. Tree growth in well-drained good soil vs. structural soil Trees on the left were planted in well-drained good soil while those on the right were in a type of structural soil All trees were planted at the same time Photo credit: Jason Grabosky, Rutgers University Structural soil

70. Tree growth in well-drained good vs. structural soil This is a photo of the same site as shown in the previous slide about ten years later Canopies have closed to form a nice shaded sidewalk Although trees on the right are growing slower than those planted in soil, all have grown acceptably and none have been replaced Structural soil

71. Tree in structural soil around parking lot island Structural soil was placed in this parking lot island and under the pavement around it Roots should grow under the pavement without difficulty because they will be growing in the uncompacted soil that is between the aggregates This is likely to allow the tree to grow to a large size and provide more benefits to the site than a tree that remains small and unhealthy Structural soil

72. Many tools at your disposal Other professionals – engineers, planners, architects, landscape architects, urban foresters, arborists Species selection and spacing Creative design solutions Ordinance and code changes

73. Urban Design to Accommodate Trees: Parking lot Solutions by Dr. Edward F. Gilman, professor Department of Environmental Horticulture University of Florida, Gainesville http://hort.ufl.edu/woody/planting