Arboriculture & Urban Forestry 32(2): March 2006 87 both potential shoppers’ and business people’s preferences and perceptions of trees in inner-city business districts. Trees are highly preferred by both groups, although business people express slightly lower liking for visual categories containing trees. Differences in attitudes regarding tree benefits and an- noyances were found, with business people rating tree ben- efits significantly lower than shoppers. Research outcomes suggest best practices for urban forest planning and steward- ship in neighborhood retail environments of large cities. (Landscape Journal 2004. 23(1):40–51) POTENTIAL HAZARD CHARACTERISTICS OF TILIA, BETULA, AND ACER TREES REMOVED IN THE HELSINKI CITY AREA DURING 2001–2003 Minna Terho and Anna-Maija Hallaksela To study decay and to improve the management and protec- tion of old urban trees, a total of 256 felled urban trees were examined during 2001–2003: 95 Tilia spp., 74 Betula spp., and 87 Acer spp. Most of the trees (73%) were located in the main parks and along the main streets in the downtown area of Helsinki City, Finland. The mean age of the trees was over 60 years, and the majority (64%) were old park trees. Poor condition and increasing risk of failure were the main reasons for felling in 82% of the cases. Thirty-three percent of these trees were degenerated or dead, but the amenity value of 14% of the risk trees was still high. The latter were old, big trees that posed a potential hazard but had a vital and balanced crown. Some characteristic profiles for potential failure were identified for each of the tree species studied: Ganoderma lipsiense in the butts and hollows in the stems of Tilia spp., weak fork formations together with Rigidoporus populinus on Acer spp., and degeneration together with decay in the stem on Betula spp. Decay fungi most commonly identified were R. populinus, G. lipsiense, Inonotus obliquus, and Piptoporus betulinus. In addition, Kretzschmaria deusta was very com- mon in three of the parks and on every one of the tree species investigated. (Urban Forestry and Urban Greening 2005. 3(2):113–120) NITROGEN STORAGE AND ITS INTERACTION WITH CARBOHYDRATES OF YOUNG APPLE TREES IN RESPONSE TO NITROGEN SUPPLY Lailiang Cheng, Fengwang Ma, and Damayanthi Ranwala Bench-grafted “Fuji/M.26” apple (Malus domestica Borkh.) trees received a constant nitrogen (N) supply (10.7 mM) from budbreak to the end of June, and were then fertigated with 0, 5, 10, 15 or 20 mM N in a modified Hoagland’s solution for 2 months during the summer. In mid-October, half of the trees fertigated at each N concentration were sprayed twice with 3% urea, whereas the remaining trees served as controls. All trees were harvested after natural leaf fall and were stored at 2°C. Five trees from each of the N treatment combinations were destructively sampled during dormancy to determine the composition of N and total nonstructural carbohydrates (TNC). As the N supply from fertigation increased, amounts of N in both free amino acids and proteins increased, whereas C/N ratios decreased. Foliar urea applications in the fall sig- nificantly increased amounts of N in both free amino acids and proteins but decreased their C/N ratios. Arginine, the most abundant amino acid in both free amino acids and in proteins, accounted for an increasing proportion of N in free amino acids and proteins with increasing N supply from fer- tigation or foliar urea application. The ratio of protein N to free amino acid N decreased from about 27.1 to 3.2 as N supply from fertigation increased from 0 to 20 mM and de- creased further to 3.0 in response to foliar urea applications in the fall. Concentrations of glucose, fructose, sucrose, and TNC decreased as the N supply from fertigation increased, whereas concentrations of sorbitol and starch remained rela- tively unchanged. Foliar urea applications decreased the con- centration of each TNC component and the TNC concentra- tion in each N fertigation treatment. A negative linear rela- tionship was found between carbon in TNC and N in proteins and free amino acids. The sum of carbon in TNC, proteins, and free amino acids remained constant in response to N supply from fertigation. However, foliar urea applications decreased the sum of carbon in proteins, free amino acids, and TNC because about 21% of the decrease in TNC carbon was not recovered in free amino acids or proteins. Young apple trees store N and carbon dynamically in response to N supply. As N supply increases, an increasing proportion of N is found in the form of free amino acids, which have a low carbon cost, although proteins remain the main form of N storage. (Tree Physiology 2004. 24:91–98) COMPARISON OF ESTABLISHMENT METHODS FOR EXTENSIVE GREEN ROOFS IN SOUTHERN SWEDEN Tobias Emilsson and Kaj Rolf The most common technique for establishment of extensive green roofs in Sweden has been using prefabricated vegeta- tion mats. Our study investigated (1) how the establishment of green roofs in Sweden was influenced by the establishment method (prefabricated vegetation mat, plug-plant, shoot), substrate composition, and species mixture, and (2) whether on-site construction was a possible alternative. The establish- ment of the vegetation, which in all cases consisted of suc- culent species, was recorded using the quadrate point inter- cept method in fixed plots and the success measured as fre- quency cover. Prefabricated vegetation mats had higher succulent plant cover than on-site constructed roofs. There ©2006 International Society of Arboriculture
March 2006
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