Protecting Trees on Construction Protecting Trees on Construction
Sites as a Stormwater BMPSites as a Stormwater BMP
Mark Grueber, Urban ForesterMissouri Department of Conservation
December 10, 2009
“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
Mark Grueber, Ecological Consulting ServicesMark Grueber, Ecological Consulting Services
Discussion Points
Why go to the effort?
Integrating trees into stormwater practices
A little tree biology -the root of the issue
Tree protection is more than protection from the bulldozer
Some methods to preserve existing trees
I am NOT a Tree Hugger!
Ok…well, maybe I
am
The science-
based, practical
reasons for
protecting trees
The economic
benefits of tree
preservation
Environmental Benefits – Storm water
controlTree age: 9 yearsSize: 28 ft tall, 19 ft crown diameter, 276 sq ft crown projection area(CPA), 1,923 sq ft leaf area, 446 sq ft stem areaSaturation storage: leaf = 0.04 inch, stem = 0.04 inchRainfall: 0.5 inchesInterception by leaf: 47.2 galInterception by stem: 10.9 galTotal interception: 58.1 galTotal precipitation in CPA: 86.1 galInterception %: 68%
These values assume no evaporation from the crown so actual interception will increase as temperatures and wind speed increase and thereby drive higher evaporation rates. *****************************************************
Greg McPherson, PhDUSDA Forest Service, PSW
[email protected], web-site:
wcufre.ucdavis.edu
Other benefits…
Carbonsequestration
Air pollution reduction
Urban heat island cooling
Wildlife habitat
Numerous psycho-social benefits
and more…
The Economics of trees as part of a
communities’ infrastructure
Trees are the ONLY part of the infrastructure that gains in value – USFS and many other resources
Increased property value
Increased tourism
Value of stormwater, pollution, and other benefits
See Midwest Community Tree Guide, General Technical Report: PSW-GTR-199 and PSW-GTR-219 for more info
How are the benefits measured?
National Tree Benefit Calculator –www.treebenefits.com
The i-Tree software suite –www.itreetools.org
CityGreen –www.americanforests.org/productsandpubs/citygreen
Tree Benefits Calculator
Tree Benefits Calculator
Tree Benefits Calculator
Tree Benefits Calculator
Common misconceptions
“We plant more
trees than we
remove when we
develop a site.”
Trees planted in
the landscape will
achieve the same
benefit of
preserved trees
Don’t trees get some credit already?
not in most municipalities
not enough to matter to most developers.
not enough to equal their true value
•Source: Center for Watershed Protection
So…what am I supposed to?
Municipalities –modify your ordinances
Engineers/planners/architects – get creative, utilize additional expertise when feasible
Citizens – teach your decision makers
and…
Approaches to use trees for
stormwater management
Incorporate trees into stormwater practices
Pursue site opportunities for stormwater forestry
Make stormwater practices an amenity
Incorporating trees into
stormwater practices
Traditionally not a
celebrated union
Some engineers don’t want
trees in STPs
Foresters want to know
where are all the trees?
Most of our practices end
up losing trees due to poor
maintenance
Challenges…
•Urban•Foresters
•Engineers/•Planners
•Now remember,
you have to work
together
•Leftover disturbed areas are not the only place for trees
•We can retain valuable trees that improve watershed functions
•We can use trees in SW practices if we design it differently
•We need wider streets and curbs
•Keep the trees in the park, we need the tax revenue
•Don’t worry, we’ll come back and plant trees later.
Trees & Stormwater: Some Conclusions
Watershed health is linked to the amount of forest in
the watershed and its distribution.
Increases in tree cover and tree size will result in
reduced total runoff and peak runoff rates (10% = 2-
5%)
Tree canopy has a greater effect on small storm events
than on large storm events (2 year storm frequency)
Effects on runoff are greatest when urban trees are
large and well-established (site quality).
Trees and stormwater management practices can
coexist if planned and designed from the start.
Protecting/Preserving trees…other
considerations
Soil – A Living, Breathing Organism
Soils from forests, woodlands,grasslands or even glades have multiple horizons including a layer of decomposing organic matter on the top
These soils are rich in organisms that aid in nutrient recycling, aeration and water infiltration
Urban Soils and Soils Disturbed by
Development
These soils have no horizons due to large scale disturbance, contain little to no organic matter and are heavily compacted for building purposes
Compacted soils have low oxygen levels which becomes toxic for soil-borne organisms
Water and oxygen infiltrate poorly
The “Typical” Planting Site?
Compacted soil base with a considerable amount of limestone chat
Confined area for plants that is shared with utilities
If existing soil is removed, compacted clay “topsoil” is backfilled creating a drastic soil interface
Protecting/Preserving trees – the
process continues
Understanding Tree Protection - How are
unprotected 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 ServicesMark Grueber, Ecological Consulting Services Mark Grueber, Ecological Consulting ServicesMark Grueber, Ecological Consulting ServicesMark Grueber, Ecological Consulting ServicesMark Grueber, Ecological Consulting Services
Root Damage from Construction
Root injury may show decline in a few months or several years
Common symptoms: yellowing or early fall color, watersprouts, dieback of small twigs and eventually major branches
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 Number Species
Diameter (in) PROTECT?
Root Pruning Comments
1 Sweetgum 18 YES Install fence as shown
2 Sweetgum 18 YES YESRoot prune along edge of proposed driveway. Install fence as shown.
3 Sweetgum 16 YES Install fence as shown4 Gingko 18 YES Install fence as shown
5 Walnut 14 YES YESRoot prune along limit of disturbance line (or remove tree).
6 Walnut 16 YES Woodland tree within protected area7 Black Cherry 14 NO To be removed8 White Oak 14 YES Woodland tree within protected area9 Black Cherry 12 NO To be removed
10 Green Ash 18 YES YESRoot prune along limit of disturbance line (or remove tree).
TREE PROTECTION ACTION KEY (for trees >12")
Tree Protection Planning
Consider design changes or constructionproceduremodifications to accommodate trees
Tunneling [alternativemeans to trenching for installation of underground utilities] instead of trenching is one of the most common
Utilize Specifications
ANSI A300 Standards
All tree protection MUST be written into constructionspecifications
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 [methodused 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
continuedAeration 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
End Result
Sustainability -
providing for current
needs of a
community without
diminishing the
prospects of future
generations
Resources
Missouri Department of Conservation Urban Forester: [email protected] andwww.missouriconservation.orgInternational Society of Arboriculture: www.treesaregood.comTreelink: www.treelink.orgBuilding with Trees Workshops – The Arbor Day Foundation: www.arborday.orgTrees and Development: A Technical Guide to Preservation of Trees During Land Development;Matheny and Clark, 1998.The Landscape Below Ground – A Series of International Conferences on Tree Root Development in Urban Soils – www.landscapebelowground.orgUp By Roots; James Urban, 2008.Center for Watershed Protection – www.cwp.orgUrban Natural Resources Institute – www.unri.orgCenter for Urban Forest Research –www.fs.fed.us/psw/programs/cufr/