ARBORICULTURE ARBORICULTU & CONTENTS URBAN FORESTRY Volume 36, Issue 1, January 2010 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) www.isa-arbor.com Pierre Jutras, Shiv O. Prasher, and Guy R. Mehuys Appraisal of Key Abiotic Parameters Affecting Street Tree Growth ................................................. 1 Abstract. Street trees must cope with severe environmental conditions. Identification of factors that modulate their survival and growth is a key process for successful management. To estimate these factors, contingency analyses were carried out using abiotic data collected locally for Norway maple (Acer platanoides L.), silver maple (Acer saccharinum L.), hackberry (Celtis occidentalis L.), green ash (Fraxinus pennsylvanica Marsh.), honeylocust (Gleditsia triacanthos L.), littleleaf linden (Tilia cordata Mill.), and Siberian elm (Ulmus pumila L.) trees. Also, compa- rable analyses were performed on a merged all-species data set. Whereas sharp differential growth was found between commercial zones and residential areas, studied species demonstrated ecological tolerance as individuals were found normally or vigorously growing in severe con- ditions. In this situation, ample irradiation intensity might be an important factor contributing to urban tree growth. Statistical analyses led to the identification of a threshold level (80% of total potential irradiation) above which optimal growth was found in commercial zones. Research results also brought out the importance of the underlying surficial deposits: slow growth rates were linked to the presence of sand/gravel depos- its. Finally, higher soil de-icing salt concentrations were found in tree pits where trees were transplanted closer to the curb and on wider streets. Key Words. Compaction; Contingency Analysis; De-icing Salt Effect; Light Irradiation; Street Trees; Surficial Deposit; Urban Zone Type. Karen Smith, Peter May, and Robert White Above and Belowground Growth of Corymbia maculata in a Constructed Soil: The Effect of Profile Design and Organic Amendment ....................................................................11 Abstract. Spotted gum (Corymbia maculata (Hook.) K.D. Hill & L.A.S. Johnson), a common street tree in southern Australian cities, was used to assess growth responses to variations in profile design and organic amendment of constructed soils. Aboveground growth responses were total stem dry weight and foliar nutrient content. The belowground response was root length density. Soil profiles were constructed of sand, amended with either coir fiber, composted biosolids or composted green waste, at rates of 0, 5, 10 or 20% by volume. The profiles were either layered, with a 150 mm (6 in) organic-amended surface layer, or uniform, with amendment of the entire profile. A single fertilizer treatment was applied to all profiles. Shoot dry weight was only affected by organic matter type with the greatest growth in sand amended with composted biosolids. Foliage P and K content were affected by amendment but foliage N was not. Profile design affected root length density and distribu- tion. Trees in uniform profiles had greater root length density, and a more uniform distribution of roots, especially with compost amendments. Above- and belowground growth increases are thought to be due to increased nutrient status resulting from organic matter mineralization. Key Words. Biosolids; Coir Fiber; Compost; Designed Soils; Root Density; Soil Amendment. Robert N. Muller and Carol Bornstein Maintaining the Diversity of California’s Municipal Forests .......................................................... 18 Abstract. Policies to promote urban forest diversity were assessed in 49 California, U.S. municipalities through a short questionnaire, fol- lowed by evaluation of street tree inventories and approved planting lists. While the majority of respondents (82%) indicated maintaining species diversity was an objective in managing their municipal forest, fewer than half of those responding positively (48%) had codified the objective in an actual urban forest management plan. Protecting against invasive species was an objective for a minority of communi- ties (24%). Street tree inventories, provided by 18 respondents, indicated a high existing diversity within the communities of the state of California (avg. 185 species per community; range 95–408). In communities where both inventories and approved planting lists could be compared directly, the number of approved species for future planting was 29% of the number of species in the existing inventory. This suggests that the future diversity of California’s urban forests may be at risk. In order to improve diversity of their municipal forests, it is suggested communities retain an experimental approach to evaluating new species, build productive collaborations with all stakeholders as well as other communities, and develop outreach opportunities to enhance public awareness of the multiple values of a diverse urban forest. Key Words. California; Diversity; Invasive Species; Municipal Forest; Urban Forest. ©2010 | International Society of Arboriculture | ISSN:1935-5297
January 2010
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