Tree Mortality and Community Forestry Program

Few people know more about tree health than the arborists and urban foresters who care for our nations street and park trees. To get an overview of the worst cases of premature tree mortality, 10 professionals representing all regions of the country were asked to rank the top 10 killers. Here are the results:

Number One Killer: Construction Damage

Every respondent mentioned this preventable cause of tree death and rated it strongly into the number one position of infamy. It is clear that a priority challenge for urban forestry programs is public education stressing the value of saving existing trees during development projects of all kinds.

Number Two Killer: Improper Pruning

If ever there was a gap between what is known in the technical sense and what is actually practiced, pruning is the prime example. Despite the research and educational efforts that have been done on this subject, respondents named poor pruning practices as the second greatest danger to urban trees. Specifically cited were topping, other excessive pruning and the kind of "flush cutting" that Dr. Alex Shigo and others have shown to break down a tree's natural defenses against the invasion of decay organisms.

Number Three Killer: Vandalism

This is one of the most difficult problems to prevent. In most cases vandalism is probably caused by an expression of anger or frustration unrelated to trees, or the actions of youngsters. Ways to prevent vandalism include; planting larger trees (minimum of 2" caliper); prune lower limbs to at least 8'above sidewalks as the tree grows; and involving residents in the selection, plaining and care of street trees.

Number Four Killer: The Wrong Tree for the Site

Poor species selection dooms many trees right from the start. Disease resistance and suitability to soil and climate conditions were mentioned as the factors most often overlooked. Planting large tree species beneath utility lines was also frequently mentioned as asking for trouble. The involvement of qualified foresters and arborists in the planning stage of all planting projects could easily eliminate this unnecessary cause of tree mortality.

Number Five Killer: Lack of Watering

A systematic means of watering during dry spells-especially newly planted trees-is one of the essentials of a well-managed urban forestry program. Enlisting the aid of local residents is one way to do this if equipment and paid personnel or contractors are not available to do the job.

Number Six Killer Poor Planting

Proper planting is essential. It requires special training of crews mid close supervision. Planting too deeply was the problem mentioned by several of our respondents. Other problems typically include rough handling of new trees, allowing roots to dry, not removing the root-bound trees without cutting or straightening encircling roots.

Number Seven Killer: Soil Compaction

Soil Compaction is one of the slower and more insidious cases of tree mortality. Mulching and regular aeration are good ways to minimize the damage.

Number Eight Killer: Bark Damage

Lawn mowers and string trimmers are the main culprits here-or, more correctly, the people who operate them carelessly. Proper instruction and supervision are key solutions, with mulch helping even more.

Number Nine Killer Misuse of Herbicides

Herbicides, especially those containing chemicals that work through reaction in the soil, should be kept away from the root zones of trees. Weed treatments on windy days should also be avoided and weed or lawn crews should be given special instruction about tree roots and how to avoid damaging them. Number Ten Killer Automobiles:

Not surprisingly, bark damage and the breakage of young trees caused by cars is a common occurrence in urban areas. Traffic barriers, proper curbs, and planting out of reach of bumper and tailgate overhang can help reduce this damage.

(This information is reprinted from the National Arbor Day Foundation's Tree City USA Bulletin No. 14, How to Kill a Tree.)