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

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

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

Photo credits: Bernardo Santos & Brad Cadwallader

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

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

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

Photo credit: Bernardo Santos & Brad Cadwallader Maintenance Options

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

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

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

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

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. 2015. The Cost of not Maintaining the Urban Forest. Arborist News 24(1): 12-16.

Implication #2 – Cost/Benefit Modified with permission of authors. From Hauer et al. 2015. The Cost of not Maintaining the Urban Forest. Arborist News 24(1): 12-16.

Implication #2 – Cost/Benefit Modified with permission of authors. From Hauer et al. 2015. The Cost of not Maintaining the Urban Forest. Arborist News 24(1): 12-16.

Implication #2 – Cost/Benefit Modified with permission of authors. From Hauer et al. 2015. The Cost of not Maintaining the Urban Forest. Arborist News 24(1): 12-16.

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. 2015. The Cost of not Maintaining the Urban Forest. Arborist News 24(1): 12-16.

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

Full Study Details…