Trees and Construction Chapter 13 ISA Arborists’ Certification Study Guide – Domains: Urban Forestry & Protection and Preservation Mark Grueber, Urban Forester
Describe how trees can be injured or killed as the direct result of construction damage. Discuss the importance of arborists’ participation in the planning stages of development if trees are to be a part of the landscape. Explain the steps that can be taken to preserve trees on a construction site. Discuss some techniques that can be used to preserve trees when the soil grade must be changed. Explain the limitations for treatment of trees that have been damaged by construction. Objectives:
Key Terms The Key Terms as listed in the Arborist’s Certification Study Guide will be defined and highlightedthroughout the presentation.
“Trees never knew complete removal of trunks, machine compaction of soils, sudden changes in water drainage patterns due to roads, pollution, and disruption of niches for soil organisms…These actions have come suddenly. They are being repeated.” – Alex Shigo, A New Tree Biology
Construction Damage to Trees One of the most common causes of tree death and decline in urban areas People want to “live in the trees” but most landowners, developers and builders don’t understand how to take advantage of the opportunity.
The Missing Link: Trees are part of the community’s infrastructure Trees are an important and vital part of a community’s infrastructure What do trees require? What do we provide in an urban/ suburban setting? Planning for trees
Elements that affect plant growth What we can’t impact Sunlight Oxygen Carbon Dioxide Soil texture (sand, silt or clay) Temperature What we can impact Available Water Available Nutrients Soil structure (how a soil hangs together) Available space
…and a professional arborist or forester to tell them that. Trees CAN be protected and preserved on construction sites A professional arborist or forester MUST be involved early – during the planning stage.
How are Trees Damaged During Construction? The most serious damage to trees caused by construction is underground. Root damage and soil disturbance.
Roots…a review. Which is a more accurate representation of a trees root system? Fine absorbing roots are concentrated in the upper few inches of the soil
Roots…the real picture Mark Grueber, Ecological Consulting Services Mark Grueber, Ecological Consulting Services Mark Grueber, Ecological Consulting Services
Root Damage from Construction Root injury may show decline in a few months or several years Remember the mortality spiral? Common symptoms: yellowing or early fall color, watersprouts, dieback of small twigs and eventually major branches
Construction Damage - Physical Injury to Trunk and Crown Damage to vascular tissues But trees heal…don’t they? Mortality spiral…again! Note the “tree protection fencing”
Construction Damage - Cutting of Roots Digging and trenching[digging to install utilities; of concern due to root damage] will likely sever roots Usually due to misunderstanding of root growth habit (1-3x branch spread) Amount of damage depends on proximity to trunk and area of root development
Cutting of Roots - continued Severing 1 root can remove 15 to 25% of root system Root loss may increase potential for tree failure
Construction Damage – Soil Compaction [Compression of the soil resulting in a reduction of the total pore space, especially the macropores] Ideal soil has 50% pore space – filled with H20 and air O2 is reduced; CO2 and other gases increase Root growth is diminished; absorption reduced
Construction Damage – Added Soil 90% of fine roots that absorb water and minerals are in the upper few inches of soil…got it??? Additional soil – even a few inches – can dramatically alter the infiltration of water and oxygen; fine roots die within 30 minutes Altering the drainage pattern may also cause significant issues
Construction Damage – Exposure Trees grow in communities with other trees and/or non-turf type plants Types of injury: sunscald, improper taper, aforementioned root and soil issues It all comes back to understanding the biology of trees and “forests”
Are there alternatives? Tree Protection Planning and Preservation Planting site improvements Soil Rooting space Conservation development – preserving a portion of trees (not on exam!)
Planning and Preservation Tree protection planning cannot wait until construction Must involve a professional arborist or forester who can communicate with developers and builders Arborist must be involved from beginning to end
Considerations of Tree Protection Planning Don’t try to save every tree! Species, size, location and condition Don’t save a hazard Younger trees may survive the stress
Tree Protection Planning Arborist – evaluates, selects and maps trees Landscape Architect – assists with plan preparation to consider other parts of infrastructure Don’t just consider the trees – remember it’s an ecosystem!
Tree Protection Planning Consider design changes or construction procedure modifications to accommodate trees Tunneling [alternative means to trenching for installation of underground utilities] instead of trenching is one of the most common
Specifications [detailed plans and statements of particular procedures and standards] All tree protection MUST be written into construction specifications All contractors (and subs!) must be made aware of these specs Consider fines (or incentives) using tree and landscape valuation methodology
Construction Damage Avoidance Barriers [fences or other means to establish a protection zone around trees on construction sites] Place as far away from tree as possible…or a minimum of 1’/1” dbh No traffic or storage of building materials, waste or excess soil NO DISTURBANCE!
Avoidance - Limit Access Limit access to one route [means of entering and leaving a property during a construction operation] on and off property – but be realistic! Remember parking. Specify areas for storage of equipment, soil, building materials; as well as areas for burning, washout, etc.
Avoidance – Compaction Reduction Build a “mulch road” - six to twelve inches of wood chips. Must be CAREFULLY removed or reused Plywood sheets
Avoidance – Grade Changes Terracing[method used to lower the soil grade in stages] Maintain original grade as far from tree as possible Must be accompanied by root pruning and care where roots are exposed
Avoidance – Grade Changes continued Tree Island[soil or landscape surrounding a tree, such as within a paved area] Similar to terracing Excellent for retaining small groves
Avoidance – Grade Changes continued Aeration systems[the set of holes or trenches created in a tree’s root area to improve oxygen availability to the roots] Tree wells[wall constructed around a tree when the soil grade is raised to maintain the original soil level and provide oxygen to the root zone] Lack of supporting research Gravel or stone below fill does NOT improve water or oxygen flow Consider tree size, species, drainage patterns, soil conditions, fill depth, irrigation and future maintenance
Avoidance – Good Communication The arborist must be involved during all phases of building Take good notes and photos This is where projects usually go wrong
“We only took the fencing down for a moment.” A tree protection plan without monitoring by an arborist is a waste of resources Very few projects result in good tree protection Plan for post-construction tree maintenance
Treatment of Construction Damaged Trees Periodic inspection and monitoring (post-construction) is a must A little turf can hide a hazard Safety first..but beware of unscrupulous contractors
Construction Damage Treatments - Pruning Remove only broken, damaged, or diseased limbs During construction limbs may have to be pruned for equipment clearance DO NOT thin the canopy to “compensate” for root loss – why?
Construction Damage Treatments – Cabling & Bracing Some trees can be preserved with remedial treatments Cables must be inspect periodically Inherent liability for the arborist
Construction Damage Treatments – Wound Repair Wounding is common on construction sites No wound dressings and STOP telling people it will “heal!” Bark tracing[cutting away torn or injured bark to leave a smooth edge
Construction Damage Treatment – Irrigation and Drainage Maintain adequate but not excessive moisture Monitor for changes in drainage patterns Most irrigation systems are inadequate and cause more harm than benefit
Construction Damage Treatments – Mulching Inexpensive and very beneficial when applied properly Use chipped bark, wood, or pine needles if possible – why? Mulch as much of the root width as practical for the landscape No volcanoes!
Construction Damage Treatments – Aeration (Vertical Mulching) [filling vertical drilled holes in the soil with materials such as gravel, perlite, peat or sand] Drill holes 2-4” in diameter; 1-3’ on center Drill holes to a 12” depth unless fill has been placed over the root system
Construction Damage Treatments – Aeration (radial trenching) [means of aerating the soil in the root zone of a tree by removing and replacing soil in a spoke-like pattern] Air excavator [device that blows air at high force; used to remove soil from the root zone of trees] Mechanical trenchers should not operate within 4-8’ of trunk Trench at least to dripline; 1’ depth
Construction Damage Treatments – Fertilizer? or “Let’s Feed that Sucker!” AGH!!! (pet peeve – this is where I go off for a while, sorry) Why is this not a good idea? If used ISA recommends a slow release to minimize risk of root injury
One More Time! Monitor, monitor, monitor. Use your knowledge of tree biology and the site conditions to guide you Obviously, this should be done by a professional…not this guy
It’s Quiz Time! Name 5 ways that trees can be adversely affected by construction: Root injury Soil compaction Injury to trunk or branches Grade change Excavation/severing root system
When soil is compacted, the ______ _______ between soil particles is reduced. pore space
Two detrimental effects of soil compaction are: Suffocation Restriction of growth
A technique used to reduce soil compaction around trees on a construction site is to spread a temporary, thick layer of _______. Mulch
The overriding objective of an arborist involved in a development project is to save every tree on the site (true/false). False…but aren’t they cute?
It is better to tunnel directly under a tree than to cut directly across the root system of a tree when excavating for utility lines (true/false). Duh.
An important action that should be taken at the start of a construction project is to erect _______ around all of the trees that are to remain. Protective fencing or barriers
Carefully cutting away loose, damaged bark is called _______ _______. bark tracing
Soils that have been compacted or raised in grade are good candidates for soil _______. aeration
There is far more than an arborist can do to treat trees that have been damaged by construction than to prevent the damage (true/false). What a dork!
_______ is a technique that may be employed to lower the soil grade in steps. Terracing
(Easy) Sample Test Questions When soils are compacted by construction equipment, trees usually decline because: oxygen availability is reduced the ability of the roots to absorb water and minerals decreases root growth and expansion may be diminished all of the above
(Easy) Sample Test Questions Arborists should be involved early in the construction planning process because: tree preservation measures should be in the specifications once construction has begun, it may be too late to save the trees there is often little arborists can do to treat construction damage all of the above
(Easy) Sample Test Questions A measure that can be taken to minimize compaction on a construction site is: water the site thoroughly before equipment is brought in permanently raise the soil grade to protect tree rots spread a temporary, thick layer of mulch over the site root prune the trees in advance
(Easy) Sample Test Questions If a significant portion of a tree’s root system has been removed during building construction, a step that will help preserve the tree is: pruning one-third of the crown to compensate for root loss a surface application of 10 pounds of soluble nitrogen per 1,000 square feet construction of a tree well none of the above
(Easy) Sample Test Questions Digging trenches in a wheel-spoke pattern and backfilling with organic matter or a more porous soil is called: radial aeration tunnel aeration soil fracturing vertical radiation
Challenge Question What actions can be taken if a tree is damaged by construction in violation of the written specifications?
Challenge Question Why may tree death and decline due to construction occur several years after construction is complete? What are some of the signs and symptoms of construction damage that an arborist can look for following construction?
Resources Trees and Development: A Technical Guide to Preservation of Trees During Land Development; Matheny and Clark, 1998. Root Injury and Tree Health; Watson Missouri Department of Conservation Urban Forester: Mark.Grueber@mdc.mo.gov and www.missouriconservation.org International Society of Arboriculture: www.treesaregood.com Treelink: www.treelink.org Building with Trees Workshops – The Arbor Day Foundation: www.arborday.org