shelter for abused landscape trees

Mechanical wounding

Also called ‘lawnmower blight’, landscape trees suffer mechanical wounding from lawnmowers and line trimmers. Justin Morgenroth published a wonderful paper in 2015, “the first formal urban tree survey designed to quantify mechanical wounding caused by lawn maintenance equipment” (Urban Forestry & Urban Greening 14 (2015) 1054-1058)

As a landscape supervisor I often fill-in for ill or vacationing foremen and so I found myself on this site line trimming. Now, from a distance the maple tree looks fine but, since I read papers on lawnmower blight, I’m always suspicious. And sure enough I noticed obvious signs of wounding. I suspect it was from both mowers and trimmers.

Reducing wounding

Morgenroth mentions three things that can reduce the chances of mechanical wounding. You can install mulch, build a tree circle or spray herbicide. In this case, the only thing I could do was to build a tree well. And I did.

Yes, trees are resilient; they can compartmentalize wounds and live on but it isn’t free. Repairs cost resources which could otherwise be used for growth.

What eventually kills trees is repeated wounding when lawn care crews visit the same site weekly or bi-weekly. My tree well should stop the abuse but Morgenroth found that even with tree wells, mulch and herbicide applications, there was evidence of abuse.

Dead landscape trees are very bad news because they require money for removal and replanting. The loss of ecosystem services makes the situation even worse. And all of a sudden it becomes a big deal; it’s not just an innocent hit to the tree trunk.

So, what else can we do? This blog post may be part of the solution: training! Landscape supervisors are encouraged to train and hold accountable their lawn care workers.

Certifications also help. In Canada we have the Landscape Industry Certified program and it’s fair to assume that certified workers are better and more knowledgeable.

Conclusion

Morgenroth’s paper suggests that mechanical wounding of landscape trees is at epidemic levels in New Zealand and the USA. I suspect, it’s the same in Canada.

Wounding stresses the trees and slows down their growth as they divert resources for repairs. Repeated wounding eventually kills them.

The recommended fixes include building tree wells, installing mulch or spraying herbicides with the aim of keeping grass away from tree trunks. A complimentary approach is training crews and holding them accountable. Crews must understand the associated costs of removing and replanting dead trees. Lost ecosystem services should also be emphasized.