Some of the benefits of urban trees Improve air quality Decrease energy costs Reduce storm water run-off Filter and reduce impurities Reduce soil erosion Increase property values Longer pavement life Improve microclimatic conditions Rain, sun, heat and skin protection Attract businesses, patrons, and new residents to a community Aesthetics
Conflict resolution and prevention Functional sewage systems and aesthetic tree environments are both essential elements of modern urban construction We need to prevent and resolve conflicts through a broad interdisciplinary approach Education Research & Development Planning Implementation Maintenance
Why do tree roots grow toward sewer lines? Water, Nutrients, & Oxygen Roots grow toward an increasing water gradient and appear to need at least a continuous surface film to direct them to the water.
Why do tree roots grow toward sewer lines? Condensation When intact drains and other service pipes are cooler than the surrounding soil, water may condense on the outer surface and root growth may develop along the moisture gradient developed in the soil.
Why do tree roots grow toward sewer lines? Heat Water flowing through sewer lines can be substantially warmer than the surrounding soil. Root growth and activity, including cell division and nutrient uptake is likely to be significantly greater than in other parts of the colder soil, leading to a mass of fine roots forming around the pipe. Thermal changes between materials provide fracture pore space.
Why do tree roots invade sewer lines? Water, Nutrients, & Oxygen Damaged lines, faulty installation, inadequate leak tightness All tree roots are opportunistic
What types of trees can be more problematic? Large, fast-growing trees with aggressive root systems: figs (Ficus spp.) maples (Acer spp.) elm (Ulmus spp.) willows (Salix spp.) birch (Betula spp.) mulberry (Morus spp.) ash (Fraxinus spp.) poplar and cottonwood (Populus spp.) large eucalyptus (Eucalyptus spp.) Sweetgum (Liquidambar styraciflua)
What types of trees are Sewer-safe? Small, slow-growing trees with less aggressive root systems: Japanese maple (Acer palmatum) crabapple (Malus spp.) Crapemyrtle (Lagerstroemia spp.) Ginko (Ginko biloba) Thornless Honeylocust (Gleditsia triacanthos var. inermis) Golden Raintree (Koelrueteria paniculata) Little Gem Magnolia (Magnolia grandiflora Little Gem) Saucer Magnolia (Magnolia x soulangiana) 'Winter King' hawthorn (Crataegus viridis)
What types of trees are Sewer-safe? There are no sewer-safe trees. Any tree will eventually take advantage of available water and colonize a sewer line.
How much of an issue are shrubs? Shrubs will exploit a broken line but root size and life span of shrubs is shorter than trees.
Dependent upon: Rooting Environment Species How far away should trees be planted?
Randrup (2001) concluded that distances up to 20 constituted the high-risk zone. How far away should trees be planted?
Estimating rooting spread and depth Root System Spread Typical Rules –3 x canopy spread not accurate –1 – 1.5 x tree height not accurate Trunk Diameter = 38:1 young trees (cannot be applied to palms or mature trees) Mordelet et al. (1996) – African fan palm ( Borassus aethiopum ) extended roots 65 before encountering nutrient-rich soil patch where root proliferation was 10x that in ordinary soil.
Estimating rooting spread and depth Root System Depth Dependent on soil profile, species, and presence of turf grass and other landscaping Majority of fine roots in the upper 12 of soil Studies have found roots up to 200 deep
Estimating rooting spread and depth Roots are opportunistic – will grow wherever environmental conditions permit Roots are not uniformly distributed around a tree Severely limited and highly irregular in urban settings
How does drought effect root growth? When first exposed to drought, the allocation of food to root growth may increase. This provides more root absorptive area per unit area of foliage and increases the volume of soil colonized. Extended drought leads to roots being suberized (corked) to prevent water loss to the soil.
How do extremely wet winters affect roots? Proliferation of roots Possible root death Too much of a good thing lack of oxygen
Root Growth Periodicity Peak growth in early summer and early fall Subterranean research is difficult and some results are contradictory At present it is still difficult to discriminate between peculiarities of species and environmentally induced reactions.
What steps can a homeowner do to control root growth? Root barriers with growth inhibitors Compact layers of soil Air gaps using large stones Solid barriers like plastic, metal, and wood. Landscape fabric (with slow release chemicals) Chemicals – sulfur, sodium, zinc, borate, salt, or herbicides (may be harmful to trees)
What steps can a homeowner do to control root growth? Root prune every 5 years (causes proliferation of roots unless followed by chemical treatment)
What steps can a homeowner do to control root growth? Recommend two clean outs be installed, one near the property line and one near the house for easier access.
What steps can a homeowner do to control root growth? Nothing is forever… except removing the tree Replace faster growing trees near older sewer lines every 8 – 10 years
What steps can a homeowner do to control root growth? Premature removal and replacement of large trees results in a substantial loss of net benefits formerly produced by the tree - approximately $70/year/tree (McPherson et al. 1999) Replacement trees are a net cost for the first 5 – 10 years because establishment costs are greater than benefits from the relatively small tree crown.
What steps can a homeowner do to control root growth? Planting Location Determine the general location of the lateral on the property. Avoid planting or maintaining trees near the lateral. For information on where-to-plant considerations, visit the International Society of Arboricultures (ISA) Webpage, Avoiding Tree & Utility Conflicts, at www.treesaregood.com
What steps can a homeowner do to control root growth? Select an appropriate species For an extensive guide on tree selection, visit Cal Poly's site (selectree.calpoly.edu) and select "low" for "Root Damage Potential" along with the other tree attributes you seek.
What can municipalities and developers do? Replacement of the vitrified clay, brick, and concrete sewer systems with modern materials and joints between pipes should prevent most root problems in the future ($$). New sewer lines made of acrylonitrile- butadiene- styrene (ABS) prevent many of the root problems.
What can municipalities and developers do? Trenchless pipe repair and replacement Relining – Acid resistant polyester fiber with resin Penetryn – liquid acrylic gel Pipe Sliplining Chemical control
What can municipalities and developers do? Standard construction methods on development sites compact the soil like a brick and then trench for the utility lines. When a tree is planted, the only un- compacted area left around the trees is the trenched area. This leads to all roots following those channels which eventually may cause line breakage. View trees as a resource for storm water treatment Professional management of tree root growth is becoming more important for all infrastructure
Improved interdisciplinary communication is needed to prevent and resolve conflicts between trees and infrastructure, which would result in lower costs and an improved environment. Technology Planning, Implementation, and maintenance Research & Development Biology