Such a deal for you! Books on trees, and pruning, and more.

Alex Shigo was a singular fellow, a noted tree pathologist, and he really knew his trees.  TPP was a postdoc on a project collaborating with Alex, not to mention working with befriending his son-in-law, Dr. Chips, and his daughter along the way.  At any rate just a few blogs ago, the topic dealt with tree injury and TPP provided a link to Shigo and Trees Associates as a source for information on pruning and tree injury.  So not only do they have highly informative books and pamphlets written by Alex, but mention The Phytophactor and get a discount!  TPP doesn't get anything, so this blog remains unsullied by money, the deal is for readers, not TPP.  You can even get a Touch Tree bumper sticker.

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.

Frost cracks in trees

Frost cracking of trees has been in the news because it does become more prevalent in very cold weather, but frost cracks are generally misunderstood, even by "tree experts". When water freezes, it expands, a rare and fortunate quality.  Most solids are denser than their liquid phase, and if this were true for water, ice wouldn't float and the other consequences are quite horrifying (read about Ice 9 in Vonnegut's novel the Cat's Cradle).  So when the water in sapwood freezes and expands it can exert enough force to forcibly crack a tree vertically, often with a loud, sharp retort.  However the ultimate cause of the crack, often determining whether the wood of a tree will or will not crack, is a prior injury to the bark and vascular cambium that often could have occurred years if not decades before. The wound healing that follows such an injury to a tree produces a radially aligned weak zone in the wood, one that extends vertically far beyond the original injury.  TPP knows this because in a former research life he spent a couple of years dissecting damaged trees under the guidance of Alex Shigo, a renown tree pathologist (his publications on trees for general consumption can be bought here).  All frost cracked trees showed evidence of prior injury, and in urban settings the most common cause of injury is lawn mowers.  Pay attention to your trees people; whacking them with your darned lawn mower isn't a good thing, nor is lawn for that matter.  Such injuries greatly limit the life span of your trees. Once frost cracked, the crack may heal over at their surface, but internally the crack remains, and it weakens the tree especially with regards to twisting forces from the wind.  So the number of trees cracking in very cold weather only makes evident the number of trees with prior wounds.  On our campus before they started putting mulch around the base of new plantings, nearly 100% of the trees were basally damaged by lawn mowing.  It is doubtful that cracks mainly occur on the SW side of trees as the wounds are more randomly placed, but real data is lacking and to say it generally occurs on one side of trees is nothing more than a tree fable. 

Impact factor - Treemendous!

This won't mean much to most of you, but this is a very nice article about the accomplishments of Dr. Alex Shigo, a guy who actually single-handedly revolutionized tree care and urban forestry.  He did this with a great deal of energy, a redwood-sized personality, a lot of research, and he summarized a lot of this information in non-technical publications.  Some of you might be interested in some of his many publications, so here's the link to Alex's publications.  Tell them the Phytophactor sent you.  Many moons have since passed since the Phactor did his post-doctoral research with Shigo and one of his associates; it was a great learning experience; we dissected a lot of trees, but unfortunately, one of the things learned was that my future was not in forestry, which at the time was quite disappointing.  In the process the Phactor met Alex's ever so lovely daughter and her husband, the ever effervescent Dr. Chips, and it was she who called my attention to this article.  She has good reason to be very proud.  Very, very few people have such a great impact on their fields.  So here's a freebie; keep those darned lawn mowers away from your tree trunks.