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Issue link: http://read.dmtmag.com/i/57838
Species Advisory Committee (CISAC) to advise the Council and develop recommendations. The CISAC com- piled its first California Invasive Species List, which was just released in 2010 (www.iscc.ca.gov/species.html). C The list has over 90 woody plants total, including 15 trees and shrubs listed with widespread impacts, and the remainder listed with more limited (at present) impacts. Some of the worst offenders I expected to find, such as tree-of-heaven (Ailanthus altissima); others I was a bit surprised to see on the list. Many of those listed in the "limited spread" category were growing wild or were planted in Redwood City's urban forest, including Chinese pistache (Pistacia chi- nensis), Monterey cypress (Cupressus macrocarpa), Siberian elm (Ulmus pumila), oleander (Nerium olean- der), and bluegum eucalyptus (Eucalyptus globulus). Even what we have been calling California pepper tree is apparently a non-native Peruvian tree, Schinus molle, and it is listed as invasive with limited spread (this was one of the surprises to me). Fortunately, none of our native or introduced oaks were on the list. In our attempts to increase diversity in the urban forest, we have planted evergreen trees now on the list, such as Monterey cypress. For fall color we have planted Chinese pistache, Chinese tallow (Sapium sebiferum), and honeylocust (Gleditsia triacanthos). For flowers, we have planted oleander and flowering plum (Prunus cerasifera). Ball moss (Tillandsia recurvata) begins to infest a Miami tree. Photo by Jeff Shimonski pruning," a micronutrient deficiency develops that can eventually cause decline and even death of that palm. This may be similar to what is happening with bromeliad infestations. When bromeliads overwhelm the canopy of a tree, the leaf litter that would normally end up on the ground, returning nutrients to the tree, is disrupted. Over time this constant nutrient capture stresses the tree and speeds its demise. Years ago, flowable copper was used to kill bromeliads. Now, spraying into the canopy of a tree to control plant parasites is almost impossible in the urban forest. The best control method at this time is early detection and hand removal before the tree is overwhelmed by the parasite and any control method becomes futile and a waste of effort. —Jeff Shimonski, Director of Horticulture, Jungle Island, Miami, Florida; Editorial Review Committee Chair, City Trees 22 We consider them good urban trees, and in many cases, the invasive potential has to do with regional and envi- ronment-specific factors. For instance, I have observed that the spread of some of the trees that are now being called "invasive" was probably due to overplanting or "mini-forest" plantings. The take-home message for me is that as we strive for more diversity in our urban forests, we need to be cautious that we don't overplant any individual spe- cies. I haven't seen reports about species that were only 5% or less of a street tree inventory explode into invasiveness. We should avoid planting trees with aggressive root sprouting. Another factor to consider is dispersion of seed by wildlife eating fruit. Yet, if we try to only plant male non-fruiting trees, we may increase the pollen issues ... proving again, there are no simple answers in urban forestry. —Gordon Mann, Mann Made Resources Consulting Arborists, Auburn, California City Trees alifornia is a large state with many different climates. In 2009, the California Invasive Species Council created the Invasive