Field of Science

Lawn mowers and trees; often not a happy interaction

As the lawn mowing season commences, TPP must remind you that trees, particularly young ones, do not like lawn mowers, not the misused machine but the idiot guiding it.  A walk through any particular neighborhood will provide numerous examples of tree abuse at the hands of lawn mowers usually in the form of gouges and missing hunks of bark near the base of the trunk.  It's the most common sort of urban tree damage.  This is simply not good, and here's the thing, such injury is forever and can have long reaching consequences that will reduce the longevity of the tree. The injury shown is not new; it's a few years old.  You can see some evidence of the wood and bark growth closing over the wound, but it does not ever completely heal. The tree compartmentalizes the wound; the cambium may over grow the wound encasing the wound in wood. Evidence of the abuse. But that's not all; where the cambium fuses together from the two sides, it forms abnormal wood for years afterward, a radial seam of weakness that many years later under stress,  particularly during the winter, can split forming what is called a "frost crack".  It's really a tree-injury crack and this has been thoroughly demonstrated by dissecting cracked trees and sure enough there is always, always, anatomical evidence of prior injury. This particular injury is also promoting some unsightly basal sprouting, which sometimes encourages lawn mowing dummies to mow even closer to trim the sprouts. The solution is to mulch a perimeter around the tree to keep the lawn mower away.  
If you want either a book or a pamphlet about tree care, you should go here.  It's a web site about the life's work and publications of Alex Shigo, a noted forest pathologist and a mentor to many of us. In particular many of these publications especially the economically priced pamphlets very useful, informative, and not technical.  These are PP approved, and if you've been reader for any time at all, you will know that this blog gives very few endorsements and is bereft of ads and popups that plague and diminish many blogs with tawdry advertising.

1 comment:

Dr Chips said...

Thank you PP for your ringing endorsement. I would note that I am now converting many of these anatomical samples that show tree responses to wounding to decorative wall adornments that also tell time. Yes, I'm making them into clocks! And in so doing I am reclaiming the space lost in my garage to the boxes that have held the samples. - Everyone, show a tree a little love and put a ring of bark around the base so you don't bump it with a mower.