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. . . . . . . . Pests Every locality has its prublems "",ith a particular insect 01' disease. The best \-vay to avoid trouble is to avoid the species that host these pests. In some cases, it is possible to bu}' varieties that have been bred for resistance to a disease. for example. \vhere vvhite pine blister rust is a problem, it is best to buy vvhitc pine that is certified to be blister rust resistant. Some species. such as goldenraintl'ec and ginkgo, arc knovvn foJ' their natural resistance to most pests. Olhers, such as American ehn. al'e just the opposite. ~ . Soil . . . . . . . . . . . . Soil factors are probably the most overlooked when selecting a tree. Soil depth, structure, and pH, in addition to soil moisture, can make the difference betvvcen slIccess or failure after planting. For example, deep-rooted species v\fill need adequate soil depth for their structural roots, vvhercas shallow-rooted species may do all right on sites \'\there soils thinly cover bedrock or a hard layer of clay Species that need light, sandy soil should not be planted in rocky 01' clay-type soils, Also, each tree species has a tolerance range related to acidit.y and alkalinity just as it does for shade. This requirement should be matched with the soil where you plan to plant. Soils are often disturbed in urban areas and trees \'\ihich \ivould typically do \'/ell may struggle due to poor soil stnJcture. Compaction of the soil due to heavy pedestrian ai' vehicle use often reduces a tree's grO\,vth and size potential. .. .'" " .. f~' 'A! - ~ ,#J I r ::~ <.' . -' - . ~~-~. ~ : ~ ~ .~. : . : :- ~:. ~ ~~~~ Air Pollution Unfortunatel}\ the ability of a species to tolerate air pollution is becoming more important. Chemicals in the air vary with localities, and in some cases the accumulative effects of pollution are just beginning to shovv up. The best course of action is to ask a local professional if there are prohlems in your to\\/11 and, if so, \-vhat species are affected. Similarly; salt spt'a)' from either the ocean or street de-icing can be a problem locally' and some species arc more sensitive to it than others. \'Vhere these are problems, ask an al'borist, nursel}: professionaL urban 1'ore5tel; or extension agent about which trees to avoid. Tip: Local nurseries generall): do not CalTY trees that are incompatible vdth the local climate. HO\vevel: for site factors other than climate. it is prelly much a mattei' of "buyer beware." Get the ans\'veI'S before 'yOll huy. III TREE CITY rSA BljLLnl~ r\u. -l-' Nation.11 :"rho!" Da.y .Foundation' 3