APPLICATIONS – TREE SURROUNDS
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HydroSTON is widely specified for pavements adjacent to or surrounding trees and landscaped areas. Such areas include footpaths, carparks and driveways as well as dedicated tree surround zones.
The porous structure of HydroSTON pavements allows air, water and nutrients to reach the root zone of vegetation and is an ideal permeable pavement for new tree plantings.
Stresses on urban trees
As noted by Cornell University’s Urban Horticulture Institute, urban trees experience a large range of impacts: soil and air pollution, heat loads, and impacts from utilities, vehicles, and buildings. The most significant problem that urban trees face, however, is lack of useable soil volume for root growth, since trees are often an afterthought in city planning and streetscape design.
When roots encounter dense soil, they change direction, stop growing, or adapt by remaining abnormally close to the surface. This superficial rooting makes urban trees more vulnerable to drought and can cause pavements to lift.
Soil compaction
Ongoing construction, including sidewalk and road repair, disturbs and compacts soil, crushing macropores (spaces between soil aggregates). Loss of macropores has three negative consequences: restricted aeration, diminished water drainage, and soil compaction making it difficult for roots to penetrate. These effects limit useable rooting space.
Role of soil volume on tree growth
The highly compacted soils required for constructing pavements, so common place in urban areas, do not allow root penetration, resulting in poor tree growth and declining tree health in the very areas most in need of shade – parking lots and streets.
Healthy trees need a large volume of non-compacted soil with adequate drainage and aeration and reasonable fertility. Structurally prepared soils can fulfill these needs while also meeting engineers’ load-bearing requirements for base courses for pavement.
Using structural soil for street trees
Structural soil is intended for paved sites to provide adequate soil volumes for tree roots under pavements. It can and should be used under pedestrian mall paving, sidewalks, parking lots, and low-use access roads. Research shows that tree roots in structural soil profiles grow deep into the base course material, away from the fluctuating temperatures at the pavement surface. One benefit of this is that roots are less likely to heave and crack pavement than with conventional paving systems.
Benedict Sand & Gravel, in association with the Australian Institute of Landscape Architects NSW, has prepared a design for Permeable Pavement for New Tree Planting. See Benedict for structural soil specification.
Lucke, T., Johnson, T., Beecham, S., Cameron, D., Moore, G., (2011): Using permeable pavements to promote street tree health to minimise pavement damage and to reduce stormwater flows, 12th International Conference on Urban Drainage, Brazil, September 2011 [PDF 760KB]
