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

egmcpherson@ucdavis.edu, 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: mark.grueber@mdc.mo.gov 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/