Published by the International Society of Arboriculture.
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SHELTERS AFFECT TREE SEEDLING ESTABLISHMENT UNDER GRASS COMPETITION
by Roger Kjelgren and Larry Rupp
Abstract. We investigated growth and water relations of tree seedlings grown in treeshelters surrounded by competing grass. Treeshelters were placed over one-year-old gambel oak (Quercus gambellii) and bigtooth maple (Acer grandidentatum) planted in field soil, and crested wheatgrass (Agrypyron cristatum x A. repens) was planted around half of the trees. Trees were irrigated only the first year. Surviving plants were counted over two years, and above-ground growth, root growth, and leaf water potential were measured the second year. Without shelters, all maples and most oaks under grass competition died within two years, while about half or more of those in shelters survived. Sheltered trees with competition had more height growth, and thus were able to extend foliage above the competing grass, and were under less water stress. Without competition, maple outgrew oak both above and below ground, but sheltered maple grew less than unsheltered maple, while the reverse was true for oak. Shelters reduced water stress in both species across all treatments. Shelters have the potential to increase seedling survival and growth when herbaceous competition is present, and increase drought tolerance, but the response will depend on the species.
URBAN FOREST RESOURCE MANAGEMENT AT HILL AIR FORCE BASE, OGDEN, UTAH
by Richard van-C. Adkins, Michael R. Kuhns, Dale J. Blahna, and Marcus W. Blood
Abstract. Most military bases can be thought of as good-sized communities, containing all of the important resources that non-military communities contain including urban forests. These military urban forests have similarities and differences with urban forests in non-military communities, and their management is in some ways different. In this paper we describe the urban forest situation at Hill Air Force Base in northern Utah, an example of a military base still in the early stages of urban forest management, but with an improving and expanding urban forestry program. The base, in cooperation with Utah State University’s Department of Forest Resources, began an assessment of its program and conducted a complete tree inventory in 1993. Inventory results and a qualitative assessment led to development of a plan with management goals and implementation strategies, which became part of an overall Natural Resources Management Plan for the Base. Besides increasing tree numbers and overall urban forest quality and tree management, the plan calls for increased emphasis on community participation as the key to a successful urban forestry program.
CONTROL OF PHYTOPHTHORA LATERALIS ROOT ROT OF LAWSON CYPRESS WITH ENTEROBACTER AEROGENES
by Raj Utkhede, Bill Stephen, and Stephen Wong
Abstract. The biological agent strain B8 of Enterobacter aerogenes, applied in June of 1992, 1993, 1994, and 1995 as a soil drench at 6.7 x 109 colony forming units per tree, was evaluated for control of Phytophthora lateralis root rot of Lawson cypress (Chamaecyparis lawsoniana) trees. The test was conducted under field conditions in the city of Vancouver, British Columbia, on naturally infected Lawson cypress trees. Based on four years of observations, strain B8 of E. aerogenes controlled the disease and increased the growth of trees. This study showed the potential of strain B8 of E. aerogenes for biological control of root rot of Lawson cypress trees.
TERMINAL BUD CLUSTER PRUNING PROMOTES APICAL CONTROL IN TRANSPLANTED SHADE TREE WHIPS
by Brian Oleksak, Monica Kmetz-Gonzalez, and Daniel K. Struve
Abstract. Transplant-induced loss of apical control, as measured by the central leader to total lateral branch caliper ratio, was documented for ‘Patmore’ green ash (Fraxinus pennsylvanica) and ‘Autumn Purple’ white ash (F. americana) by measuring trees one, two, five and 10 years after transplanting. For both species, the central leader to total lateral branch caliper ratio ranged from 0.3 to 0.5, regardless of the age from transplanting, indicating that large lower limb development (loss of apical control) was initiated at transplanting and persists for up to 10 years. Transplanted nursery grown ‘Patmore green ash and ‘Autumn Purple’ white ash trees bud pruned to maintain a strong central leader had central leader to total lateral branch caliper ratios of 0.7 and 0.8, respectively. A pruning treatment, removing the lateral buds from the terminal bud cluster, reduced large lower limb development, maintained apical control and resulted in better lateral branch distribution in transplanted red oak (Quercus rubra) and ‘Patmore’ and ‘Autumn Purple’ ash whips than leaving the terminal bud cluster intact.
VITALITY, VARITATION, AND CAUSES OF DECLINE OF TREES IN OSLO CENTER (NORWAY)
by Oddmund Fostad and Per Anker Pedersen
Abstract. To document the health of the most important city trees, a total of 1243 in the Oslo center were surveyed during a five year period. The most frequently planted species in the street environment were Acer platanoides, Aesculus hippocastanum, Tilia platyphyllos, and Tilia x vulgaris. Street trees had poorer health and more severe leaf scorch than park trees. Frequent symptoms of stress on street trees were chlorosis, small chlorotic leaves, necrosis, stem injury, dead twigs and branches, and pest attacks. For some species pests were significantly higher on street trees than in park trees. Tilia platyphyllos and Tilia x vulgaris had the highest ratios among the most commonly planted species. They tolerated the difficult growth conditions along streets surprisingly well, but were often attacked by linden spider-mites which can periodically be a serious problem. Acer platanoides and Acer pseudoplatanus received the lowest ratio and suffered in many cases from severe decline. Aesculus hippocastanum and Betula pendula showed intermediate fitness to street conditions. The most critical factors affecting the tree growth in the Oslo center, were de-icing salt (NaCl), stem injury due to lack of space for tree growth, pest attack, and relatively high soil pH.