TREE PROTECTION MEASURES
"All trees, regardless of where they are growing, are genetically 'forest' trees. ... The closer you can keep trees' environment to that of a forest, the healthier the trees will be." (Marx, 1995, p. 4.)
Decline and/or death of trees might not become evident until many years later. Some authorities allow as short a time as one to three years (Britton, 1992, p. 10). Many are less specific (Dreistadt, 1994, p. 41; Harris, 1992, p. 467; Schoenweiss, 1982, p. 169). Shigo (1986, p. 553) extends it to even ten to twelve years after construction injury. Coate (1983, p. 26) notes that it may be fifteen or more years following changes beneath patriarch oaks.
Most authorities emphasize that the root zones may well be the most important part of our trees on construction sites. The root zones of most trees extend well beyond the spread of the branches, and 80% to 90% of their absorbing root systems are in the top 6" to 12" of soil, maybe having some of the larger laterals down to a depth of 3' (Hagen, 1991, p. 3; Harris, 1992, p. 309; Shigo, 1986, p. 197; Watson, Dec. 1985, p. 39; Willeke, 1992, p. 54). this is in contrast to the standard 6th-grade science book which has shown a 40' tall tree with a mirror-image, 40' deep, root system. In reality, root systems are much more pancake-shaped, and we must take this into consideration.
Tree Protection Measures
A tree's root zone environment must be taken into account. The more roots which can be left undisturbed, the greater a tree's chances of survival five or ten years beyond project completion. Modern literature states that most of a tree's absorbing root system is in the top six inches of soil, likely 80% within the top twelve inches. (Watson, 1985, p. 39; Harris, 1992, p. 309; Shigo, 1986, p. 197.)
Where measures cannot be taken to care for a tree, planning for its early removal and replacement might be more prudent than needing unanticipated removal after its subsequent demise.
General Tree Protection
FENCE: Protective fence must usually be installed surrounding the trees to be saved. For the ideal configuration, locate the fence to maximize the exclusion of traffic over the root zones, preferably at the drip lines. The fence shall remain in place, standing and continuous, until the final grading stage of the project.
UTILITIES, TEMPORARY: Any temporary construction site utilities (electric, water, communication, etc.) shall be placed so as not to affect foliage crowns or roots of trees to be retained.
CLEAN-UP AREA: Cement forms, paint brushes, plastering tools, and such, must not create a mess with clean up contaminating root zones.
DEMOLITION: Caution must be exercised around trees to remain; root zones must not be compromised.
TUNNELLING: Tunnelling under roots is preferable to severing.
EXCAVATION: Manual excavation and pruning methods will be used when encountering roots with a diameter exceeding 2" to avoid the extensive damage which heavy equipment does to roots.
EXPOSED ROOTS: Where it is necessary to cut into a root zone, newly severed or exposed roots shall be protected.
POWER EQUIPMENT: Equipment operators should be informed that machinery can cause great injury to standing trees. They must take unique care to operate with as much distance as possible between machines and trees -- branches, trunks, and roots. Any accidental damage must be promptly repaired by a qualified arborist.
CHEMICALS: No storage, pouring, or leaking of any fuel, oil, or chemical may be allowed beneath a tree's canopy. Time is of the essence in the event of any size spill; prompt containment and proper clean-up is necessary.
USE: No signs, wires, or other construction apparatus may be attached to any tree.
FOLLOW-UP: Monitor for health & vigor: Trees should be inspected upon project completion as well as at appropriate intervals to note changes and developing situations which could require action: foliage crown density, weight distribution, and/or breakage; pests; diseases; cables and supports; root zone moisture and oxygen; et alii..
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