CHAPTER 4. DISTURBANCE AND URBAN 



FOREST HEALTH 



Introduction 



An urban or community forest is the sum 

 of planted landscape trees and remnants of the 

 native forest intentionally or inadvertently left 

 behind during the building of the city. Urban 

 forestry is the discipline concerned with man- 

 aging these forests. 



Urban forest health is less than ideal — 

 The health of Oregon's and Washington's com- 

 munity forests is poor in many towns and cit- 

 ies. Erratic maintenance, old age, lack of 

 species diversity, insects and diseases, devel- 

 opment pressures, and weather combine to 

 create a myriad of problems for urban trees. 

 Although Oregon and Washington have been 

 at the forefront in traditional forest manage- 

 ment, their urban forestry practices have 

 lagged significantly behind other regions of the 

 United States. 



Most community forests have aging or 

 overmature trees. Many of these trees were 



planted and left without adequate care, and 

 others simply were the wrong trees in the 

 wrong places. In Oregon and Washington cit- 

 ies, tree replacement consistently lags behind 

 tree removal, but recent surveys of Northwest 

 communities show that tree planting is in- 

 creasing. 



East of the Cascades, environmental 

 changes, tree age, and pests are taking a great 

 toll on community trees. Historically, the re- 

 gion was planted with a few hardwood species, 

 such as black locust, Siberian elm, poplars, 

 and various conifers. Although tenacious, 

 these species have characteristics some people 

 consider undesirable, such as weak wood, 

 messy fruit, and prolific sprouting, which can 

 result in high maintenance costs. Replacing 

 them with a diverse selection of more appro- 

 priate species or cultivars will reduce mainte- 

 nance costs and improve the health of the ur- 

 ban forest. 



Tree topping stresses urban trees. Many land- 

 scape trees have suffered from "topping, " the practice 

 of indiscriminantly removing the large branches in the 

 crown of a tree. Because trees need leaves to pro- 

 duce energy, removing the canopy causes trees to 

 slowly starve. With this stress, trees become more 

 susceptible to insect and disease damage. Wounds 

 created by topping provide places of entry for decay 

 organisms. The resulting decay often goes unseen 

 and undetected until the tree fails. Dead wood and 

 poor branch structure also contribute total and costly 

 tree failures. 



Li^Lj--L ii^ 



Urban — 60 



