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 Michael R. Kuhns
Abstract. Successful transplanting requires that woody plant roots quickly grow from the root ball, through any packing materials, and into the surrounding soil. Burlap is a common packing material on medium to large root balls; it may be untreated or treated to resist decay, or synthetic "burlap" may be used. Many people believe that roots can easily and quickly penetrate burlap and therefore such materials can be left on the root ball at planting, saving time and decreasing root disturbance, but possibly interfering with root growth after planting. This study was done to determine whether Norway maple (Acer platanoides L. ) roots could readily penetrate treated and untreated burlap left on root balls during transplanting. I found that the presence of untreated or treated burlap had little or no effect on root growth from the original root ball. Untreated burlap decayed quickly, though the double layer decayed more slowly. Treated burlap did not appear to decay markedly over the course of the study and evidence was found that it can cause root girdling later on. Management implications and recommendations are discussed.
By Geoffrey P. Arron, Sally de Becker, Harrison A. Stubbs, and Eugenia W. Szeto.
Abstract. A multi-year field program was conducted in California and Nevada to determine the efficacy of tree growth regulators (TGRs). At 37 sites, trees were trimmed and treated with paclobutrazol, flurprimidol, dikegulac or uniconazole by trunk injection, tree implants, or bark banding. Tree growth was determined over a period of 1-4 years for 12 common West Coast species. Growth was determined by measuring increase in tree height. At most sites that were not compromised during the study, the TGRs had no detectable effect on growth. Inhibition of growth was observed over 4 years at one site with London plane (Platanus acerifolia) trunk-injected with uniconazole, at one site with big leaf maple (Acer macrophyllum) trunk-injected with uniconazole, and over 2 years at one site with Chinese elm (Ulmus parvifolia) trunk-injected with paclobutrazol or uniconazole. Trunk injections and bark banding of flurprimidol inhibited the growth of blue gum (Eucalyptus globulus) over 2 years at one site. There was a lack of consistency in the effects observed; for example, the growth of London plane was inhibited at only one of eight sites. Possible explanations for the low level of effectiveness and lack of consistency include site variability, tree water relations, and hole spacing. Problems were experienced while conducting this large-scale research effort under field conditions. Factors that contributed to a low level of effectiveness and a lack of consistency need to be addressed to improve the cost-effectiveness of the product formulations evaluated.
By James R. Clark, Nelda P. Matheny, Genni Cross and Victoria Wake.
Abstract. We present a model for the development of sustainable urban forests. The model applies general principles of sustainability to urban trees and forests. The central tenet of the model is that sustainable urban forests require a healthy tree and forest resource, community-wide support and a comprehensive management approach. For each of these components, we present criteria and indicators for assessing their status at a given point in time. The most significant outcome of a sustainable urban forest is to maintain a maximum level of net environmental, ecological, social, and economic benefits over time.
By Cecil C. Konijnendijk
Abstract. In Europe, more attention is being given to the concept of urban forestry. However, it is applied more to forests under a strong urban influence than to urban greenspace at large. Urban forests especially differ from other forests in terms of the dominance of local actors in policy-making processes to determine which functions the forests should fulfill. As large parts of Europe have become urbanized, these forests are extremely important particularly as pressures on nearby recreation settings and on Europe's urban forests are high.
In the context of a European study of urban forest policy-making, a tentative overview of urban forestry history is presented. In spite of existing cultural, socio- economic and political differences between countries and cities, some general developments can be described. Over time, more forests have become incorporated and planted in and near urban areas, with a growing number being opened to the public. Urban forest policy-making processes have become more complex, involving a larger number of people. The role of urban forests in the development of forestry practice and science deserves special mention.
By Robert K. Witmer, Henry D. Gerhold, and Eric R. Ulrich.
Abstract. Two experiments investigated the effects of tree shelters on height, caliper, and diameter growth of liners of 14 species and cultivars. In the first year at one nursery all nine varieties had greater height growth inside shelters, averaging 325% of controls without shelters, thus adding 1.1 feet (33 cm) to 2.3 feet (70 cm) to their height. After two years at the other nursery, the varieties had increased height growth inside shelters ranging from 111% to 484% of controls, or 0.3 feet (10 cm) to 4.2 feet (128 cm). Caliper growth either was adversely affected by shelters, as much as 0.4 inch (1 cm) in two years, or did not increase in proportion to height growth. Trees in shelters were less sturdy, but other studies indicate caliper growth in subsequent years may overcome this disadvantage.