Published by the International Society of Arboriculture.
Select a title from the list below to see an abstract of the article. For information about ordering reprints of complete articles, contact ISA at (217) 355-9411 or isa@isa-arbor.com.
By John W. Groninger and John R. Seiler
Abstract. Soil-applied paclobutrazol has been shown to reduce tree growth and pruning costs in trees occupying utility rights-of-way. Uptake and efficacy of soil applied chemicals is often influenced by soil texture and moisture status at the time of application. To test the influence of these conditions on paclobutrazol efficacy, Profile 2SC growth regulator (DowElanco) was applied at three rates (control, 0.3 or 0.6 ml ai/cm stem diameter) to potted sweetgum and white pine seedlings under factorial combinations of soil texture (clay loam or sandy clay loam) and water availability (drought or well-watered). Under well-watered conditions, terminal leader elongation was reduced 53 and 23% by paclobutrazol for sweetgum (Liquidambar styraciflua) and white pine (Pinus strobus), respectively. Sweetgum shoot elongation was responsive to paclobutrazol in the clay loam, but not the sandy clay loam soil. Sweetgum total leaf area and specific leaf area and white pine needle length were reduced by paclobutrazol treatments across water availabilities and soil textures. The results of this study suggest that drought during and following application of paclobutrazol does not reduce efficacy of this chemical. Further research is needed to clarify the impact of soil texture on paclobutrazol efficacy.
By Jeffery K. Iles and Joanna S. Stookey
Abstract. A survey questionnaire was sent to all 180 active members of the Iowa Nursery and Landscape Association to assess the importance of crabapples (Malus sp.) to the nursery and landscape industry in Iowa, identify crabapple taxa offered for sale, and characterize consumer preferences. Most of the respondents (83%) identified crabapples as their customers' preferred flowering tree, with cultivars ‘Prairifire', ‘Spring Snow', and ‘Snowdrift' as the most popular taxa. Slightly less than two-thirds of all respondents indicated they had eliminated certain crabapple selections from their product line. The cultivars ‘Radiant' and ‘Royalty' were cited most frequently as discontinued taxa, primarily because of disease problems. Businesses must continually evaluate the appropriateness of the crabapple taxa they carry to insure they are offering only those selections with excellent ornamental utility and superior disease resistance.
By Jeff L. Sibley, D. Joseph Eakes, Charles H. Gilliam, Gary J. Keever, and William A. Dozier, Jr.
Abstract. Four red maple (Acer rubrum L.) cultivars (‘Franksred' - Red SunsetTM, ‘Northwood', ‘October Glory', and ‘Schlesingeri') grown in containers were evaluated for response to different photosynthetically active radiation (PAR) levels. As PAR increased, there was a linear increase in net photosynthesis (Pn) and transpiration (E) for ‘Franksred' and ‘October Glory'. In contrast, Pn and E for ‘Northwood' and ‘Schlesingeri' increased as PAR increased to about 1375 µmol·m-2·s-1 and 1350 µmol·m-2·s-1, respectively and declined thereafter. PAR had no relationship to water use efficiency (calculated as Pn/E) for the four cultivars. Mesophyll resistance (rm) to CO2 (CI/Pn) decreased linearly as PAR increased for ‘October Glory'; but ‘Franksred', ‘Northwood', and ‘Schlesingeri' exhibited a quadratic response to PAR (with estimated lows of 17.61 cm·sec-1 at 1600 PAR, and 16.45 cm·sec-1 and 16.36 cm·sec-1 at 1400 PAR, respectively). The enhanced photosynthetic mechanism for rm as PAR levels increased suggests that ‘October Glory' is the most adapted cultivar of the four selections in this study for high PAR environments. Furthermore, adaptive ranges of red maple cultivars may be predicted during developmental stages by establishing light curves for Pn, E, and rm.
By D. Mark Browning and Harry V. Wiant
Abstract. A study was conducted to examine the economics of deferring line clearance tree pruning. The cost of pruning a tree was found to increase significantly as it grows closer to, and beyond, the conductors. The amount of biomass, and thus disposal cost, also increases with the length of time a tree is allowed to grow. Predictive models were developed for three utilities to provide a means of projecting the total impact of postponing line clearance work on crew time and costs associated with pruning trees. For every routine maintenance dollar deferred, substantially more than one dollar must be spent in subsequent years to re-establish the preferred cycle. The specific amount of this increase is utility dependent and is affected by production costs, tree growth rates, site characteristics (dbh and type of pruning), etc. An additional adjustment would be necessary to allow for an increase in disposal costs resulting from a larger amount of biomass removed. If funding reductions are not offset with larger expenditures in subsequent years, tree maintenance cycles are rapidly extended. Modeling a 20 percent annual funding decrease resulted in extending one utility's cycle from 5 years to 9 years over a 12-year period. These estimates do not take into account the impact that deferred line clearance work has on service reliability, service restoration costs, and the amount of time spent on hotspotting and responding to customer requests for unscheduled maintenance.
E. Thomas Smiley, Donald H. Marx, and Bruce R. Fraedrich
Abstract. Trees growing in forest soils have abundant mycorrhizae. This association increases nutrient and water absorption, increase tolerance to stresses, decreases root disease and is, therefore, important in maintenance of forest health and vigor. Certain species of ectomy-corrhizae improve survival and growth of pine and oak seedlings on clear-cut reforestation sites, on forestation sites in the tropics, and on adverse sites, such as coal mined lands and borrow pits. The application of mycorrhizal technology in forestry and mine reclamation is at the commercial level.
Recently, a preliminary study showed that the fine roots and ectomycorrhizal development were significantly increased by inoculation with spores of Pisolithus tinctorius (Pt) on 25 to 46 cm caliper (10 to 18 in.) northern red oak (Quercus rubra) trees growing on a man-made landscape in Michigan. There is an obvious need to further test the application of mycorrhizal fungi on established landscape trees. The purpose of this project was to determine if inoculations with spores of Pt alone or in combination with slow release nitrogen fertilizer, would improve the density or development of fine roots and ectomycorrhizae on established residential trees. A secondary goal was to determine if there was significant supplantation of the naturally- occurring ectomycorrhizae on treated trees.
By Douglas T. Still and Henry D. Gerhold
Abstract. A study of reasons why people volunteer for urban forestry projects, and of their task preferences, compared the opinions and attitudes of volunteers with those of people in botanical organizations who might be considered likely targets for recruitment. A mail survey used membership lists of two tree volunteer organizations and one botanical garden in New York City, as well as one tree volunteer organization and one arboretum in Philadelphia. Members of the three tree volunteer organizations had completed a training course on tree care or inventory, and may not be representative of volunteers typically involved in single-day projects. Collectively, 1,038 people were sampled and 63% responded. Tree volunteers were predominately white, middle aged, well educated, and financially middle class. Improving one's neighborhood was the main reason for volunteering, followed by desire for education; social interaction was only moderately important. Respondents from all organizations considered tree care to be the most important urban forestry task. Volunteers thought tree care would provide the greatest personal satisfaction compared to other tasks, while potential volunteers thought planting trees would be most satisfying. Education was regarded as a highly important task to gain public support, even more important than tree planting. Respondents were least willing, by a large margin, to engage in fundraising or lobbying politicians. Both volunteers and potential volunteers were willing to perform a wider range of tasks than they have performed already, suggesting strong potential for increased involvement. Tree volunteers expressed a strong desire to increase their level of participation in the planning and decision-making of their projects. Less than half of the volunteers thought they had been recognized for their work in some way, but recognition was mostly viewed as unimportant. Respondents from all organizations felt that their urban forest was in rather poor condition, and that volunteers are needed to improve their city's trees. Four-fifths of potential volunteers have volunteered before in some way, indicating a general willingness for voluntary action by members of botanical organizations. Many current tree volunteers were self-motivated in seeking volunteer involvement; i.e., they responded to media announcements and volunteered without being personally asked. However, personal contact with potential volunteers is an effective recruitment technique for expanding the pool of volunteers beyond this self- selected group, as well as for increasing diversity.