Field Work & Findings
Assessing health and future cost of urban trees in Guelph

1. QUALITATIVE DATA

  • A survey with 8 health indicators

  • Calculating health scores of trees in pits and berms

2. QUANTITAVITE DATA

  • Measuring and comparing trunk and root flare

  • Considering outliers

3. COST BENEFITS

  • Analyzing long-term planting cost of trees in pits vs on berms  

 

1. Qualitative Data
Each of the 24 Kentucky Coffee Trees was given a health score using these indicators

Health Indicators (scored by)

  1. New growth (1-4)

  2. Canopy density (1-4)

  3. Canopy evenness (1-4)

  4. Center leader (0-2)

  5. Leaf colour (1-2)

  6. Root flare (1-5)

  7. Soil surface area (0-4)

  8. Distance to hard edge (0-3)

Pit-graphic-white.png

Pits

AVG. health score: 9.8

Qualitative Data Results

Trees living in berms received higher health scores than those planted in pits

Berm-graphic-white.png

Berms

AVG. health score: 23.3

Qualitative Data Health Score Chart.001.jpeg.001.png
 

2. Quantitative Data
Two standard trunk diameter measurements were taken from each tree

Quantitative measurements:

  1. Diameter at Breast Height (DBH): Trunk diameter at ~4ft height

  2. Diameter at Ground Level (DGL): Trunk diameter at ground level (root flare)

Pit-graphic-white.png

Pits

  • Mean DBH: 13 cm

  • Mean DGL: 18 cm

  • Susceptible to trunk damage 

Quantitative Data Results

Berm trees showed more growth than pit trees

Berm-graphic-white.png

Berms

  • Mean DBH: 15 cm 

  • Mean DGL: 22 cm

  • Berm provides physical protection 

Comparing Trunk and Root Flare Growth

ComparingTrunk-RootGrowth.png

Percentage Increase

While a 2-4 cm difference may not seem significant, this translates into:

  • a DBH 15.4% larger

  • a DGL 22.2% larger

 

Simply from planting in berms! When excluding 2 outliers this amounts to 21.6% and 31%, respectively.

 

3. Cost Benefits

Calculating future cost of trees at $400/tree (provided by the City of Guelph) in a 100-year cycle based on a 3.7% annual mortality rate (Roman, L.A.; Scatena, F.N.2011)

CostBenefitsResults.png
Pit-graphic-white.png

Pits

  • In a 100-year cycle:

  • 44 trees will die

  • Each tree will be replaced 4-5 times

  • Cumulative cost $22,560

Cost Benefits Results

Berm-graphic-white.png

Berms

  • In a 100-year cycle:

  • All trees expected to live to full life span

  • Zero re-plants

  • Cumulative cost $4,800

How Many Pit Trees Need Replacing In 100 Years

FOR A 100-YEAR CYCLE:
The city is expected to spend
(25,000 trees x $400) = $10,000,000

If the city plants 250 trees/year with annual mortality rate 3.7%

By year 100, there will be 6356.79 surviving trees instead of 25,000.

The consequence of planting trees in pits is a loss of 18,643.21 trees for a 100-year cycle. 

How Much Will It Cost The City To Continue To Plant Trees In Pits
Each tree will be replaced 4 to 5 times

Over $7million
IN 100 YEARS

Nearly 75% of the city’s 100-year budget of $10,000,000 will have been used for replacement trees

  • Case study selection and project guidance by Martin Ford, Horticulturist

  • Field work by Magdalena Sobol, PhD, Martin Ford, and Judy Roeder

  • Research, statistics and analysis by Magdalena Sobol, PhD

  • Project photography by Magdalena Sobol, PhD

  • Slide presentation by Katarina Savic, Nicole Valkova, Magdalena Sobol