Agenda - Parks and Recreation Commission - 10/14/1993

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hoes. Minimize damage by avoiding excavation during hot, dry weather; keeping the plants well watered before and after digging; and covering exposed roots with soil, mulch, or damp burlap as soon as possible. PA VEMENT Sidewalks and driveways located' too close to a tree endanger its health and may threaten pavement stability. · Factors such as frost heaving, poor drainage, and pavement flaws give roots an opportunity to expand, gain a foothold, and cause damage. . Homeowners are faced with costly repair bills and p~tential liability for the hazardous situation that develops· These problems can be avoided if · you consider the spatial needs of a tree and its root systerr~en ~ning the layout of new sidewalks and driveways, Just how much space i~ required depends upon a tree's sensitivity to root cutting and its future size (Table I). It's best to locate .sidewalks and driveways outside the anticipated PRZ. At a minimum, walkways should be at least three feet · from the trunk of a tree; driveways ma), dover up to half the distance from th~ tree's PRZ to its trunk, as long as . no excavation occurs. No tree should be. boxed into an area less than eight. : feet by eight feet by three feet, with larger ire,,,' receiving at least 300 cubi~ - feet of root/soil volume. " '~ .You can minimize disruption by using alternatives to conventional . · paving materials. In some communi- ties, brick or flagstone.walkways on sand foundations can be substituted fo~' conCrete (FigueTe 10). These materi, · ~.ls protect soil pH and allow water: '.' and oxygen penetration..Preserve ' · natural contouring by spanning · uneven areas with,wooden walkways eie'vated on posts.' Elevated decks are excellent alternatives to concrete porches..¢'here additional pavement' i strength is needed (e.g., driveways),: -concrete requires less excavation.than asphalt. Ask your builder obout raised pa'vemeht techniques near valuable trees. ': block .... chips/grovel Figure 10. Paving moleriols such os brick or/togs tone over sand will produce less disruplion fl]uti poured concrete to the roots at o nearby tree. There are several techniques for repairing pavement that has been damaged by protruding roots. For trees thai are highly sensitive to mot disturbance, consider creating a concrele or asphall "mini-ramp" lo smoolh Ibc uneven surface between two sidewalk sections (Figure 11 ). Local ordinnnces governing liability should be consulted prior to using this technique. Relocate wnlkwnvs with broken concrete slabs a few feet farther from the tree. For trees that can tolerate root disturbnnce, n vertical underground barrier may redirect tool expansion away from pavement (Figure 12). All tree species are capable of causing root damage to sidewalks, foundations, or pipes. Species nolori- ous for dama~qusing roots are noted in Table 1. Ft~Ture 1I. A "mini-romp" can be used to smooth [i]e uneven surface caused by root damage to pavement, . root control I. ' barrier "&-~. .- ' J' ~.1 sidewalk . ' ' ' curb .: '" Flgur~ 12. A Vertical underground barrier will help keep tree roots from damaging barterer e as they gro~: