1. Dr. Justin Morgenroth Mr. Brad Cadwallader Mr. Bernardo Santos
A case study on the impacts of lawn maintenance activities on Christchurch’s urban forest
Dr. Justin Morgenroth
Mr. Brad Cadwallader
Mr. Bernardo Santos
NZ School of Forestry

2. The Ecosystem Services Framework
Provisioning services
Food/fuel production
Regulating services
Air pollution reduction
Stormwater management
Cultural services
Health
Recreation
Supporting services
Habitat provision
Diverse
Threats
Healthy
Abundant

3. Lawnmower Blight
“One of the most frequent causes of damage to trees […] comes from lawn equipment” – University of Kentucky
“Each year a large number of trees […] are severely injured and die from lawn maintenance equipment” – Penn State
Photo credit: Brad Cadwallader
Finish by asking this question and come back to it in the results
Photo credit:Bernardo Santos

4. Photo credits: Bernardo Santos & Brad Cadwallader

5. Study Details
Objective: Determine the incidence and severity of mechanical wounding caused by lawn maintenance activities
Measurements: Species, DBH, # of wounds, presence of surface roots, mulch?, spray ring?, grass cutout?
Assumed that wounds were caused by lawn mowers or line trimmers
Study trees:
1018 trees across 308 plots stratified randomly in 16 parks, reserves, cemeteries, public universities, and grass verges (private) in Christchurch, NZ
surveyed trees ranged from 3 – 253 cm DBH and represented 116 different species
Plots were 20m radius plots

6. Results 62.9% of 1018 trees had at least one wound
Surface roots are a predisposing factor:
93.6% of 389 trees with surface roots wounded
43.9% of 629 trees with no surface roots wounded
We analyzed pubic and private trees separately to begin with and determined that there was no difference between the two that allowed us to subsequently analyze all trees together.
Photo credit: Bernardo Santos

7. Frequency of Wounding 371 trees (37%) had no wounds
181 trees (18%) had more than 10 wounds
87% of trees with 10 or more wounds had surface roots

8. Photo credit: Bernardo Santos & Brad Cadwallader
Maintenance Options

9. Maintenance Options Grass next to stem 67% had mechanical wounding
No grass next to stem
59% had mechanical wounding
within 30 cm of
Photo credits: Bernardo Santos

10. Implications of Results
Reduced growth and vigour
Increased costs, decreased benefits
Photo credit: Brad Cadwallader
Photo credit: Bernardo Santos

11. Implication #1 – Wounding, Growth, and Vigour
If you know anything about trees in NZ, you know that they grow very quickly, so a Liquidambar that’s 22 years old should be much larger
2007 Liquidambar styraciflua Planted in 1985
2008
Mulch applied, but too late
2009
RIP
Slide content provided by Brad Cadwallader

12. Implication #1 – Wounding, Growth, and Vigour
1st wound in 1986
2nd wound in 1987
3rd wound in 1988
4th, 5th, and 6th wounds in 1991
Again in 2002 & 2004 and a further 4X until tree died in 2009
Trees are also like elephants! They never forget.
Slide content provided by Brad Cadwallader

13. Implication #2 – Cost/Benefit
I sat down with the urban foresters in Christchurch to talk about what the research meant to them. They were less frustrated by the cost of removal and replacement than they were by the lost benefits.
When growth is compromised or the premature mortality occurs, the cost /benefit graph is changed drastically.
The next 6 slides add one series at a time to show how mechanical wounding reduces benefits and increases costs such that net benefits are reduced drastically.
Modified with permission of authors. From Hauer et al The Cost of not Maintaining the Urban Forest. Arborist News 24(1):

14. Implication #2 – Cost/Benefit
Modified with permission of authors. From Hauer et al The Cost of not Maintaining the Urban Forest. Arborist News 24(1):

15. Implication #2 – Cost/Benefit
Modified with permission of authors. From Hauer et al The Cost of not Maintaining the Urban Forest. Arborist News 24(1):

16. Implication #2 – Cost/Benefit
Modified with permission of authors. From Hauer et al The Cost of not Maintaining the Urban Forest. Arborist News 24(1):

17. Implication #2 – Cost/Loss of Benefits
Summarize the change from a scenario with no mechanical wounding to a scenario with mechanical wounding. The net benefit decreases dramatically.
Modified with permission of authors. From Hauer et al The Cost of not Maintaining the Urban Forest. Arborist News 24(1):

18. Conclusions…
Lawnmower blight is a threat to ecosystem services in Christchurch, New Zealand
Surface roots are a major predisposing factor
Get rid of grass around the stem
New solutions needed to minimise the epidemic
This research was never going to produce ground-breaking, counter-intuitive results. There’s enough anecdotal evidence to suggest that mechanical wounding is a problem.
But the real contribution of this research is to quantify just how much of a problem it really is.
62% of all trees affected by mechanical wounding
93% of trees affected if they have surface roots

19. Full Study Details…