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Tree Preservation During Construction:
An Evaluation of a Comprehensive Municipal Tree Ordinance
Kaitlyn Pike a, Dr. Keith O’Herrin b, Dr. Christie Klimas c, and Dr. Jess Vogt d
aM.S. Environmental Science, DePaul University, bCity Forester, Highland Park, IL cAssociate Professor, DePaul University dAssistant Professor, DePaul University
Support &
Funding
PURPOSE
JUSTIFICATION
HIGHLAND PARK, IL
RESEARCH QUESTIONS
METHODS
1. How many residential trees did the City’s ordinance preserve?
2. What is the overall size and condition of residential trees?
3. Are tree preservation ordinances effective in protecting the CRZ?
4. Can we predict tree mortality for trees on redeveloped properties?
To better und erstand the role of munici p al forestry ord inances in tree
preservation and the long-term effect that residential development has
on trees intended to be preserved during construction
Question 2. What is the overall size and condition of residential trees?
RESULTS
74%
26%
Preserved Removed
Question 4. Can we predict mortality
for trees on redeveloped properties?
URBAN FORESTS IN U.S.
•Represent 35% of all urban land cover (Nowak et al., 2010)
•Deliver benefits to 2/3 of the population (U.S. Census Bureau, 2015)
•Provide many ecosystem services (Roy et al., 2012)
•$18.3 billion net annual benefits (Nowak and Greenfield, 2018)
URBAN DEVELOPMENT HAS LED TO
•Rising urban populations (UN DESA, 2018)
•Reduced canopy cover (Nowak and Greenfield, 2012; 2018; 2020)
•Reduced diversity (Raupp et al., 2006; Dolan, 2015; Groffman et al., 2014)
•Ecosystem disservices (Lyytimaki and Sipila, 2009; Campagne et al., 2018)
TREE ORDINANCE
•A law enacted by local government
•Protects and manages community trees
•Tree planting, removal, maintenance
•90% of communities in U.S.
(Hauer and Peterson, 2016)
•Most regulate public trees
•Less common to regulate private trees
•U.S. cities = 40% residential (Dwyer et al., 2000)
•Gap exists in municipal knowledge and power
TREE PRESERVATION ORDINANCE
•Tools that establish sta nd ards
•54% of communities in U.S. (Hauer and Peterson, 2016)
•Improve tree condition and decrease tree mortality
(Landry et al., 2010; Hauer et al., 2020; Hilbert et al., 2020)
•Guide homeowners / developers
•Economically beneficial
(Morales, 1980; Dombrow et al., 2000; François et al., 2002)
•Mature trees = more valuable
(Lindenmayer and Laurance, 2017)
BACKGROUND
The Critical Root Zone (CRZ) is defined as a 1-foot radius for every 1 inch in trunk diameter (Abbey, 1998).
Tree preservation ordinances can help protect the CRZ by implementing tree protection zones or areas.
•Suburban city: 25 miles north of Chicago
•Population of ~30,000 residents
•Median household income ~$148,000
•Median housing value of ~$575,000
•49% canopy cover (CRTI, 2017)
•~30,000 public trees:
•City Forester, Assistant City Forester, Intern
•2019 UF budget of $1,027,600
Tree Preservation Ordinance
•Passed March 1991
•Classifies all trees over 8” DBH
•Protected, Key, Heritage
•Based on species and size
Building Permits
•Pre-construction inventory
•Tree preservation plan
•Tree removal permit
•Replacement trees
•Fees in lieu of planting
Question 3. Are tree preservation
ordinances effective in protecting CRZ?
Question 1. How many residential trees did the City’s ordinance preserve?
Complete demolition and re-development of
residential properties, beginning in the year 2004
and having been completed by the end of 2015.
•Query of City’s permit database
•Case files searched to eliminate non-viable sites
•Tree preser vation plans scanned
•Permit numbers used for homeowner notices
Properties that had not experienced construction in
the past 50 years (i.e. comparison sites) were found
via permit database.
1220 of 1652 trees remained = 74%x (z = -2.6941, tau = -0.192483, p = .007)
Table 1.
Condition index adapted from an inventory manual created by the University of Minnesota’s Department of Forest Resources
(North, 2014); Deductions in Crown (0 -4) and Trunk (0 -4) Condition are subtracted from an 8-point index total.
Crown Condition (up to 4 pts) Crown
Deductions
Index
Condition
Stag Heading Tip Die Back Symmetry Live Crown Ratio
0 - 4
8.0 subtracted
by Total
Deductions
Tot al P os si bl e
Points Deducted
1.0 0.5 1.0
25% or less 2.0
33% or less 1
50% or less 0.5
Trunk Condition (up to 4 pts) Trunk
Deductions
Cambium Loss Decayed Wood Sprout / Sucker Stem Cracks
0 - 4
Tot al P os si bl e
Points Deducted
3.0 4.0 0.5 2.0
p-value= .007
21 22.8
8
13
18
23
28
33
Study Comparison
Trunk Diameter (in)
(n=645) (n=140)
p-value= .012 p-value < .001
3.75
6.94
4.01
7.32
0
1
2
3
4
5
6
7
8
9
10
Condition (1-5) Index (0-8)
Condition and Index Condition
Study Comparison
(y= 0.862489
-0.006856x)
Property-level: 17 trees before → 13 trees after = 4 trees removed
0
50
100
150
200
250
300
0- 10 11-20 21-30 31-40 41-50 51-60 N/A
Trunk Diameter (in)
Preserved
Removed
Thank you! kaitlynpike@gmail.com
kpike@mail.ubc.ca
Any questions or comments? J
What does this research tell us about the efficacy of tree preservation ordinances?
NO Tree Preservation Ordinance Tree Preservation Ordinance
Size Mature trees = more likely to be removed
(Anderson and Barrows-Broaddus, 1989; Koeser et al., 2013) Protects mature trees
Proximity
Proximity to new buildings = more likely to be
removed (Elmes et al., 2018; Guo et al., 2018)
Proximity has no effect on
tree condition or mortality
Soil
Compaction
Soil compaction caused by construction site
traffic (Randrup, 1997; Randrup and Dralle, 1997) Protects CRZ of trees
244 272
0
50
100
150
200
250
300
350
400
Tree Preservation Area Building Activity Area
Soil Compaction (Psi)
(n=103) (n=83)
= EFFECTIVE AT PRESERVING TREES DURING AND AFTER CONSTRUCTION OCCURS!
Logistic regression w/ binomial distribution found that
DBH was only sig explanatory variable for mortality
•For every 1-inch (2.54 cm) ↑ in DBH, a tree is ~1% more
likely to remain after construction occurs
Soil in Tree Preservation Area was significantly
less compacted than soil where building
activities occurred freely
Study trees = 1.8-inch smaller DBH Study trees = ↓ condition scores
Preservation rate ↓ as % impervious surface ↑
*Does not account for cause of death from pest/disease
p-value= .049
