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HomeMy WebLinkAbout2005 05 11 Attached Distributed by Mike MingeaDate: May 11, 2005 ATTACHED BOARD BY ARB ORI S T DISTRIBUTED TO MIKE MINGEA, THE CITY Quarterly Newsletter of the Florida Urban Forestry Council . Counc~ WIND RESISTANCE IN TREES Winter/Spring 2005 Examples include live oak, ma nolia, sweet-gum, and most palms. I addition, trees should not' be planted clo er than twenty feet from astructure w th acon- ventional foundation. This not my reduces potential for damage f om limb failure, but also allows for ade uate ' access to prune the canopy and; if neces- sary, roots next to the foundation. While we have less control over mature trees in the landscape, it is helpful tq: know the relative wind resistance of each species. Trees near structures that aze inherently weak-wooded, e.g., chinaber- ry, sugazberry and maple, probably . should be removed. However, it is impor- tant to note that maturity is a relative term (Zetween species, and younger trees have greater elasticity due to fewer age- related structural faults. Therefore, in some cases it may make,more sense to keep the young maple, but remove the aging laurel oak. Another factor affecting wind resistance in trees is conformation. Research has continued on page 2 Probably only poets and azborists have What determines whether a tree is a deep thoughts concerning trees. Typically, friend or foe? While there aze no hurri- ~ trees are viewed as benign from a mainte- cane-proof structures including trees, cer- end Resistance In Trees ......................................................18 2 Hance perspective or as beneficial tain characteristics afford wind resistance. President's Message ............:.._.................................................3 because of their ability to cleanse the air, These include type or species of trees; Profiles "People, Places and Projects" ........................................3 moderate temperatures and add beauty to age of trees; placement of trees in land- 2005 FUF(Membership ......., :..................................................4 FUF(New 8 Renewing Members : 5 the urban landscape. However, in the scape; conformation and vitality of trees; ..... .......................................... Trees Florida 2005 6 wake of hurricanes Charley, Frances and and tree maintenance practices. Some .................................................................. Trees porida 2005 Awards Program ....:..... 1 Jeanne it has become evident that trees species of trees are generally more ................................ Adverfising Information ............................. . ........ . .. 1 also can be destructive. It is this dual durable and flexible than others, particu- .... ............... . . The Nistory of Arbor Day .........................:................................8 nature of trees that has sensitized Florida lazly those with wide-angled limb attach- The Weak Versus The Strong Among The Street communities and generally created a neg- ments. Trees In South Florida ..........................................................9 ative public perception. Now more than Urban Foreshy Programs Benefit (ommu~ities -large ever, it is important to disseminate valid This type of information is useful in 8 Small ....................................:...............................10 811 azboricultural principles to practitioners selecting trees to plant in the residential Membeahip Application ...................:......................................11 and homeowners. landscape. FUF(ExecuHve (ommitteg Members ........................................12 ~' By Steve Graham, Tampa Municipal Forester continued from page 1 :.' demonstrated that certain growth charac- teristics result in stronger trees. While some species and individuals have a propensity to develop a strong growth form, it must be cultivated in others. In a corollary, the Florida Division of Plant Industry publishes current grades and standards to guide the nursery industry in growing strong and healthy trees. Structural failures in trees may well be a relatively rare occurrence for future gen- erations. While volumes have been written on tree structure, a summary statement might read: maintain a single, dominating trunk to promote securely attached primary branches with optimal vertical and radial separation for growth and exposure to sunlight. In addition, natural crown shape and proportions should be encouraged, particularly with respect.to the overall height of the tree. This allows for flexing under wind loads, which dissipates energy while stimulating the development of taper in the trunk and branches. The formation of opposing compressed and tensioned reaction wood reinforces wind resistance. Moreover, a full crown of foliage more effectively dampens, sheers and deflects potentially damaging winds. The industry recom- mends that two-thirds of the height of the tree should be maintained in foliage. If a mature tree with a full crown can moderate the force of wind, then by extension a grove of trees can do it even more effectively. Not surprisingly, farm- ers for centuries have employed shelter- belt trees for soil conservation and crop protection. Also, anyone who has stood in the middle of a forest on a windy day has sensed the calm. Similazly, it is practical to plant trees on close centers, i.e., 20-25 feet because the resulting canopy is one integrated and fortified unit. Also, healthy trees have better wind. resistance than trees in poor condition. The proper ratio of essential minerals is needed for adequate formation of lignin, cellulose and mood fibers to confer strength. Just as important is water poten- tial of trees. When soil moisture levels are adequate, water-conducting vessels are turgid and there is greater elasticity. This enables trees to bend and flex under a wind load with less breakage. However, it should be noted that water, which weighs six pounds per gallon, could add significantly to the tonnage of a tree. This can be problematic when combined with structural faults. Too much rainfall can saturate soils and allow lazge, spreading trees to be wind- thrown. Wet soils are fluid and offer little resistance to roots being pulled from the ground under the weight of a leaning tree Many mature live oaks were lost this way from hurricane Jeanne. It is ironic that there was little crown damage to this species, which seems to have excellent wind resistance. As a sidebar, utility trenching and construction too close to trees contributed to the wind-throw of many species during this event. opened up. Also, the sudden exposure to sunlight can lead to sunscald, decay and decline in trees. Understandably, residents are now more concerned about large tree limbs over houses. However, removing a primary limb that originates from the trunk will only provide a false sense of security. Primary limbs are structural and develop load-bearing capability over time and in relation to other limb and trunk compo- nents. Eliminating, a primary limb over a house may negate a counter weight ~ Finally, the maintenance history of a tree opposing other forces at play within the has some bearing on wind resistance. The tree. The problem is compounded from most important maintenance activity is increased exposure to turbulence; and proper pruning. The torque fror~i wind objective is to main- y. tain a full crown of "The objective is to maintain a full activit foliage, but to crown of foliag e, but to remove How shou ld storm remove dead or damaged imbs be dying branches on dead or dying branches on an pruned? ~ e ANSI " A300 sta an annual basis. annual basis dazds pro- However, it is . vide the a borist important to note with info ation that embedded bark and ensuing decay at needed to make a variety of cut depend- branch connections initiated most branch ~ ing upon intended purpose. The most failures from hurricane Jeanne. This common practice is to remove a`~damaged , could be avoided by maintaining a dorm- limb back to parent branch or to ~ lateral nant trunk and retarding rate of growth of branch large enough to assume lead and competing branches with reduction cuts. support growth and maintenance. This not only promotes strong limb However, this can result in the unneces- attachments, but also improves defense sazy loss of structural components and a against decay. warehouse of stored energy in the form of organic compounds. Also, removing a Often it is not inaction, but rather inap- primary limb back to the trunk exposes a propriate action that renders trees haz- larger volume of wood to decay. ardous during a storm event. Heading back primary limbs to some arbitrary ~ While there is some timidity in the indus- point, i.e., "topping," has long been rec- try, reduction cuts or heading to a node ognized as damaging to tree struct~_ may be a more acceptable alternative to Not only does this expose a larger vol- compromising structure, resources and ume of wood to decay, the resulting defense. In the short term, this means sprouts are weakly attached and as they leaving some calculated stubs, which is increase in size are more apt to split out not aesthetically appealing. However, and fall on a target. Amazingly enough, latent or dormant shoot buds can be there aze utility companies that still do trained over time to resume growth and not grasp this most fundamental princi- ple. The other extreme involves removing excessive interior foliage from a tree, i.e., lion-tailing under the pretext of reducing "sail" This is a very damaging practice that interferes with the tree's ability to develop proper taper for wind resistance. Moreover, wind loads are applied to sepa- rate branch components resulting in amplified stress and leverage at trunk connections. Branch failure generally occurs at attachments. However, in some species, e.g., southern red cedar, branches will break internodally when the crown is function within the crown. These "restorative" cuts are consistent with the standards and are a practical approach to maintaining the integrity of a tree. In the event that a tiee is destroyed, don't forget that mature trees have substantial value and a tree appraisal may be used in claiming a casualty loss for income tax purposes. Hurricanes have created a lot of work for the tree industry. They have also created the opportunity to promote arborist certification and pgofessionalism within the industry. We have an ethical obligation to reach out and reassure the public concerning proper tree care.