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Dysfunctional Root Systems and Brief Landscape Lives



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Dysfunctional Root Systems and Brief Landscape Lives Stem Girdling Roots and the Browning of Our Landscapes Gary Johnson Consider this comparison of potential life spans for trees Burns and Honkola 1990 USDA 1998 Quercus macrocarpa bur oak in upland site 250 years Acer saccharinum silver maple in riparian site 125 years Acer negundo boxelder in lowland site 100 years Pinus banksiana Jack pine in field site 80 years Betula papyrifera paper birch in northern lowland forest 65 years Tree planted in urban core street site T hat s a sobering thought a tree with a normal life span of 65 to 250 years may live less than 10 years when planted in any American city s downtown landscape Admittedly that figure represents tree placement in the worst of our urban landscape sites sidewalk cut outs These inhospitable planting sites are also known as tree coffins tree burial mounds or urban tree disposal units to frustrated urban foresters When the mortality rate of downtown trees is compared to tree losses from Dutch elm disease oak wilt sudden oak death and gypsy moth it doesn t take too long to realize that there s an epidemic of urban tree loss going on and it s largely under the radar Figure 1 Another oft quoted number is that the average urban residential tree lives for 30 to 35 years Moll 1989 That life span is three times as long as a sidewalk tree yet only half as long as a paper birch in its natural environment Growing conditions in residential landscapes may not be quite as bad as sidewalk sites but there are many natural and unnatural pressures on the trees that lead to briefer landscape lives Residential landscape soils can be as stressful as downtown sites poorly drained outrageously alkaline subjected to blends of every pesticide less than 10 years known to modern society and compacted to such a degree that lawns may seem like nothing more than green concrete With few exceptions perhaps tornadoes and a few diseases there are no angels of death that descend and quickly



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