City Trees is a premier publication focused on urban + community forestry. In each issue, you’ll learn how to best manage the trees in your community and more!
Issue link: http://read.dmtmag.com/i/65193
as wind, rain, ice, snow, or flush of growth. Fort Worth saw a 13% increase of Priority 1 work orders to mitigate tree risk last summer over the previous summer, but we believe this is only a preview of things to come. Our records indicate that after a prolonged dry, hot period, the volume of emergency response work orders spikes with the next load-bearing event. Statistically this most often occurs during spring winds and/or storms in April or May. The volume of broken limbs hanging and in the street could increase dramatically this year. Total tree failure can occur when trees already structur- ally compromised by trunk cavities, dry rot, or leans are further weakened by internal drying and cracking. In some instances, extremely dry soil lacked the cohesive strength to hold a leaning or unbalanced tree upright. Midsummer, an otherwise healthy 42-inch- (107-cm) diameter pecan (Carya illinoinensis) tree fell on parkland in Fort Worth because of soil failure. Last year's drought caused decreased vigor and death to many trees throughout the state. Some species are more susceptible to drought than others. One of the species hardest hit in Fort Worth was the American elm. By the end of summer, forestry staff reported that all American elms had shown signs of drought stress. We conservatively estimate that 25% of the 3,863 American elms growing on the parkway will need removal or prun- ing due to drought stress within the next one to three years. Early estimates predict that 66,000 City trees will need some form of hazard mitigation within the next one to three years due to drought stress. Forestry crew's current work capacity is 19,000 trees annually. The Texas Forest Service was quick to respond by pro- ducing a flyer and video on proper watering of urban trees. The City of Fort Worth added the video to their home page and forestry staff added a link on their email signature line. Over a thousand trees planted within the past three to ten years were given emergency water dur- ing the scorching summer by forestry and park employ- ees as well as volunteers. Despite supplemental water, thin-barked trees could not withstand the prolonged high temperatures. Red oaks (Quercus rubra) and mag- nolias (Magnolia sp.) across the City of Fort Worth were cooked to death. In Fort Worth, we treated the 2011 drought as any other debris-generating event with the luxury of an extended reaction time. By late summer we had park employees counting and marking dead and severely stressed trees on park property. Forestry staff was in the middle of a street tree inventory and modified data collection to include drought-stressed trees. With these numbers we were able to project a cost to the City for removal. Forestry worked feverishly over the winter to mitigate hazards before spring storms. Because of our projec- tions, we were spared this fiscal year's hiring freeze. www.urban-forestry.com The City tree farm lost over 1,500 trees to high temper- atures and water stress. One employee spent 80% of his time last summer repairing irrigation lines damaged by water-starved rodents and other wildlife. With water shortages across the state and a prediction by meteo- rologists that the drought would extend into 2012, we made the decision to concentrate transplanting efforts on container stock which required more water to main- tain than field grown stock. Once the container grown tree was in the ground, it would require less water than in the nursery. In this way, we were conserving water by transplanting trees. Unfortunately, our tree-planting partners, intimidated by water rationing, were pulling out of projects. A campaign was initiated to generate public interest in planting trees on City property. On average we plant 1,600 trees each year on public land; we are projecting 1,000 this year. Mitigation is two-part: remove risk, and reforest. Without benefit of spreading limbs and cooling transpiration, our cities in Texas will suffer hotter temperatures, more stormwater runoff, and greater number of ozone days. Our role as urban foresters is more important than ever. —Melinda Adams, City Forester, City of Fort Worth, Texas Conditions in south-eastern Australia is making things more unpredictable. Years of drought have been followed by widespread flood events and destructive tropical cyclones (hurricanes) in the north- ern tropics. Australia is definitely a country of 'droughts and flooding rains'. have always been challenging, but climate change In Adelaide, South Australia, we have a Mediterranean climate with an annual rainfall of 550mm (21.7 inches). We have recently come out of a seven-year drought, coupled with water restrictions, which saw many large, mature trees give up and die. Some of these trees were over a hundred years old. We had to come up with strat- egies to try to save the remaining urban forest. This included planting species that are drought-resistant, like yellow gum (Eucalyptus leucoxylon 'Goolwa Gem'), wilga (Geijera parvifolia) and tuckeroo (Cupaniopsis ana- cardiodes). These species are hardy, adaptable to poor soils, can handle salt and wind, and appear to be pest and disease resistant. Mulching of established and newly planted trees has played an important part by retaining soil moisture and providing favourable condi- tions for beneficial organisms that help to improve soil health and condition. When planting new stock, we use soil conditioning addi- tives including hydro-absorbent granules which swell quickly on contact with water to help retain moisture in the root zone. Combining this with a slow-release 21