Robert Bush 8:35 a.m., May 25
Love, Death, Poverty, and Beauty: Urban Trees II
Due to unpopular demand, the following is offered as an extension of the first installment of "Love, Death, Poverty, and Beauty: Urban Trees" http://www.sandiegoreader.com/weblogs/earth-fire-and-water/2013/jan/30/love-death-poverty-and-beauty-urban-trees/?c=138460
Palm "trees" can be a preferable alternative to many other true trees for planting along streets, particularly in the shallower soils of San Diego's "mesas" where the presence of impenetrable "hardpan," commonly overlain by clay, prevent deep enough penetration by roots to properly anchor and support many trees that have been commonly planted in such places. The main reason for this is that palms have many small roots that are stronger in their totality, much in the way that cables consisting of many small wires can be stronger than a solid steel rod of the same composition and diameter.
While falling fronds certainly can cause some damage and injury, they are not so deadly as a broken branch from a true tree, such as some species of Eucalyptus which have caused considerable damage and deaths. Perhaps the most notorious species for shedding large branches and falling is the blue gum eucalyptus (E. globulus), but, for this reason, yet perhaps primarily because it is notorious for being "dirty," producing considerable litterfall consisting of its much larger seed pods, strips of bark, leaves and small branches, it is almost never planted and the old ones which remain are few in number. It is not particularly aesthetically pleasing either.
The sugar gum (E. cladocalyx), while not as troublesome or as "ugly" as the blue gum eucalyptus, may be a serious competitor for the blue gum's reputation for dealing death and destruction and cost of maintenance. The sugar gum is a beautiful tree, and Balboa Park is loaded with them. They are the very tall ones that make such a pretty, lacy pattern of leaf clusters at the ends of branches against the sky. Many of them are as much as 100 years old or more, and are very tall. Many of these trees have fallen in Balboa Park and elsewhere, and branches can fall without warning. This makes these trees exceedingly expensive to properly maintain; what is almost laughingly termed "a safety trim" can cost thousands of dollars, and puts tree maintenance people at great risk. The practical result of these factors leads to a de facto “policy” of “safety” trimming only a fraction of the total large tree population.
While the sugar gum is perhaps the most numerous species that poses a potential danger from falling branches and the entire tree falling, it is not the only potentially dangerous species—in fact, some other species might have an even higher propensity for falling and limb-drop than the sugar gum. The fact that it is so numerous and is present in areas of very high public use makes it more likely to be the species involved when such events take place.
Palms also are better suited to the narrow “parkway” strips of land between curbs and sidewalks where most street trees are planted. Lacking the big roots of “real” trees, they do not lift up sidewalks, curbs, and streets the way the real trees do. However, these features do not automatically provide safety; palms can shed fronds and fall over when their root systems are compromised by disease, digging, drought, and malnutrition.