Tree Protection Zones by Arborists for All Construction Project Phases

Summary: Kelby Fite and E. Thomas Smiley of Bartlett Tree Research Laboratories cover tree protection zones defined by arborists for all construction project phases.

Sturdy, visible fences identify tree protection zones during construction project phases: Peter Bedker/Bugwood.org, CC BY 3.0, via Forestry Images

Tree protection zones assure preservation of woody plants when TPZs appear in all five phases of construction projects, according to Preserving Trees during Construction for the October 2016 issue of Arborist News.

Kelby Fite and E. Thomas Smiley of Bartlett Tree Research Laboratories bid architects, developers, engineers and landscape architects to bring arborists into all construction project phases. Planning, design, pre-construction for demolition and site preparation, construction and site servicing and post-construction for fencing removal and final landscaping constitute the five construction project phases. Planning phases define and evaluate soils, topography and trees for placement, size and type of buildings and infrastructure to be documented in design phase site plans.

Tree resource evaluations ensure retention of desirable, healthy, preservation-suitable, stress-resistant mature, medium-age and young species by inventorying crown density, foliage color, injuries, pests and shoot growth.

Inventories of coarse-textured, compaction-resistant gravelly, sandy soils, of clayey, compaction-susceptible, organic matter-poor, wet soils and of targets throughout all construction project phases fill tree resource evaluations.

Risk assessment and mitigation of pre-construction, construction and post-construction tree failure-impacted activities, people and property guide arborist-recommended maps of tree locations and of tree protection zones. Arborist-recommended locations hinder indirect damage to trees for burn pits, debris piles, drainage and utility corridors, excavations, fuel-mixing, grade changes, parking, site traffic, storage and washouts. Tree conservation plans subsequent to resource evaluations and supplementary to preservation maps identify soil compaction controls, tree protection zones and trees for retention or for transplant.

Design phases juggle permanently retaining groups of trees for shared root spaces and sustainable perimeters and temporarily buffering valuable trees with smaller trees along woodland edges.

All construction project phases ideally keep tree protection zones of mixed-age, mixed-species, structural defect-free trees that know no co-dominant trunks, low live-crown ratios or suppressed crowns.

Drip-line methods link the tips of the canopy's longest branches into a ground-level, trunk-centered circle for locating healthy, stable roots and soils within construction project fencing. Breast-height (dbh) trunk-diameter measurements made at 4.5 feet (1.4 meters) above the ground, and multiplied by factors mentioning damage tolerances and relative tree ages, mark TPZs. The presence of excurrent trees to be retained permanently or temporarily despite asymmetric, small or suppressed crowns or despite leaning trunks necessitates TPZs by trunk-diameter methods.

Lopsided perimeters offer a third option for trees that operate with "irregular rooting areas" or with root losses on one side that occasion expanded opposite sides.

Educational sessions hosted by construction project arborists promote soil and tree safety awareness among contractors during the bidding process and among construction workers during pre-construction phases.

Four- to 6-foot- (1.2- to 1.8-meter-) tall fencing of chain-link, wire-mesh or wood qualifies as "highly visible," "solidly anchored," "sturdy" barriers throughout all construction project phases. Unavoidable TPZ intrusions require 0.75-inch- (2-centimeter-) thick mats or wood atop 4-plus-inch- (10-plus-centimeter-) thick woodchip mulch or 6- to 12-inch (15- to 30-centimeter) mulch atop soil. Four- to 6-inch- (10- to 15-centimeter-) thick gravel atop staked, taut geotextile fabric likewise serves as manually applied, manually removed minimizers of root and soil damage.

Construction-tolerant, mixed-age, mixed-species trees preserved through arborist-involved resource evaluations, site maps, tree conservation plans and tree protection zones tuck brand-new construction into the site's best woodwork.

Visible barrier around tree at drip-line during construction protects tree roots: Peter Bedker/Bugwood.org, CC BY 3.0, via Forestry Images

Acknowledgment

My special thanks to:
talented artists and photographers/concerned organizations who make their fine images available on the internet; University of Illinois at Urbana-Champaign for superior on-campus and on-line resources.

Image credits:

Sturdy, visible fences identify tree protection zones during construction project phases: Peter Bedker/Bugwood.org, CC BY 3.0, via Forestry Images @ http://www.forestryimages.org/browse/detail.cfm?imgnum=5028086

Visible barrier around tree at drip-line during construction protects tree roots: Peter Bedker/Bugwood.org, CC BY 3.0, via Forestry Images @ http://www.forestryimages.org/browse/detail.cfm?imgnum=5050037

For further information:

Fite, Kelby; and Smiley, E. Thomas. October 2016. "Preserving Trees During Construction." Arborist News 25(5): 12-17.

Gilman, Ed. 2011. An Illustrated Guide to Pruning. Third Edition. Boston MA: Cengage.

Hayes, Ed. 2001. Evaluating Tree Defects. Revised, Special Edition. Rochester MN: Safe Trees.

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