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Predictive Equations for Dimensions
and Leaf Area of Coastal Southern California Street Trees
Paula J. Peper, E. Gregory McPherson, and Sylvia M. Mori
Abstract. Tree height, crown height, crown width, diameter at
breast height (dbh), and leaf area were measured for 16 species of commonly
planted street trees in the coastal southern California city of Santa Monica,
USA. The randomly sampled trees were planted from 1 to 44 years ago. Using
number of years after planting or dbh as explanatory variables, mean values
of dbh, tree height, crown width, and leaf area responses were modeled
using two equations. There is strong correlation (adjusted R2
> 0.70) between dbh as a function of number of years after planting, and
total height, crown diameter, and leaf area as a function of dbh. Correlation
is weaker between measures of crown height and dbh. This is probably due
to crown pruning increasing the variability among measurements for trees
having the same or similar dbh. Equations for less-intensively pruned species
displayed adjusted R2 greater than 0.70. Equations are presented
for predicting dimensions and leaf area and applied to compare tree sizes
and growth for all species 15 and 30 years after planting.
Induction
of System Acquired Disease Resistance in Plants: Potential Implications
for Disease Management in Urban Forestry
Glynn C. Percival
Abstract. Systemic acquired resistance (SAR) is the phenomenon
whereby a plant’s own defense mechanisms are induced by prior treatment
with either a biological or chemical agent. The concept of SAR has been
widely recognized and studied for the past 100 years in relation to increasing
resistance to fungal, bacterial, and viral pathogens of economically important
crop plants. The use of SAR as part of a disease management strategy
in relation to urban forestry has received little scientific investigation
despite offering some potential for tree pathogen control. The objectives
of this paper are to discuss the concepts of SAR and, where applicable,
indicate how SAR may be incorporated into a disease management system by
urban foresters. Areas discussed include historical background, persistence
of SAR, mechanisms of SAR, induction of SAR by biological organisms and
chemicals, interplanting with flowering woody plants to promote an SAR
response, and SAR in woody plants.
Effect of Urban Expansion on Arbuscular
Mycorrhizal Fungal Mediation of Landscape Tree Growth
Linda B. Stabler, Chris A. Martin, and Jean C. Stutz
Abstract. Field and glasshouse pot studies were conducted to
determine effects of urban expansion on arbuscular mycorrhizal fungal (AMF)
populations and AMF impact on landscape tree growth. Soil and root segments
were collected and evaluated for root colonization by AMF of trees at remnant
Sonoran Desert sites and nearby, formerly desert, drip-irrigated residential
landscape sites in the Phoenix, Arizona, USA, metropolitan area. Native
desert trees had greater colonization by AMF than residential landscape
trees, and AMF species composition differed at the two site types. A glasshouse
pot experiment using AMF inocula from the desert or residential sites was
used to evaluate AMF effects on growth and carbon fluxes of three landscape
trees in 12-L (3-gal) polyethylene containers relative to non-AMF controls.
Growth and P nutrition of Acacia smallii and Fraxinus uhdei
were increased by AMF colonization. Acacia carbon assimilation was increased
by AMF root colonization. Soil respiration by Acacia and Fraxinus
tree roots was decreased by AMF root colonization. Growth and carbon fluxes
of Parkinsonia microphylla were not affected by AMF. We conclude
that AMF might significantly increase landscape tree carbon storage potential
depending on tree species, AMF population characteristics, soil water availability,
and improved P uptake.
Effects of Cover Sprays and Residual
Pesticides on Scale Insects and Natural Enemies in Urban Forests
Michael J. Raupp, John J. Holmes, Clifford Sadof, Paula Shrewsbury,
and John and Davidson
Abstract. Cover sprays and residual insecticides are tactics used by landscapers and arborists to control arthropod pests on trees and shrubs in urban settings. Trees in residential landscapes that received three cover sprays annually for at least 4 years harbored a greater diversity of scale insect pests and were much more likely to be infested with scales than trees in landscapes treated with cover sprays for shorter periods of time. Oak (Quercus palustris) trees in an institutional landscape treated with residual insecticides harbored significantly lower numbers of beneficial arthropods than trees treated with a pesticide that lacked residual activity. The suppressive effect of the residual insecticides on natural enemies was pronounced on the community of parasitic wasps that attack the obscure scale (Melanaspis obscura), a common scale insect pest of oak. The effect of residual insecticides on individual wasp species persisted 4 weeks after the pesticides were applied. By reducing the use of cover sprays and residual insecticides, arborists may be able to conserve communities of natural enemies in managed landscapes. This will enhance the biological diversity of beneficial insects found in urban forests and thereby aid in increasing their sustainability.
Response of Amphibian and Reptile
Populations to Vegetation Maintenance of an Electric Transmission Right-of-Way
Richard H. Yahner, William C. Bramble, and W. Richard Byrnes
Abstract. A 2-year study of amphibian and reptile populations was conducted on a 500-kV transmission line right-of-way (ROW) of PECO Energy in the Piedmont Physiographic Province, Montgomery County, Pennsylvania, U.S., from June through July 1999, September through October 1999, and March through October 2000. The objectives were to compare the diversity and relative abundance of amphibians and reptiles between the ROW and the adjacent forest, among five treatment units on the ROW, and between wire and borders zones on treatments on the ROW. Eight species were observed during the study, and the two most common species were Jefferson salamanders (Ambystoma jeffersonianum) and redback salamanders (Plethodon cinereus). All eight species were noted on the ROW, but only Jefferson and redback salamanders occurred in the adjacent forest. The number of species ranged from six species in the mowing plus herbicide unit to three each in the stem?foliage spray and foliage spray units. All species were found in the wire zones compared to only five species in the border zones. The ROW contained a greater diversity of amphibian and reptile species than the adjacent forest. Because forest-management practices can have negative impacts on populations of amphibians and reptiles, this study provides valuable information on forest-management practices required for the conservation of amphibians and reptiles.
Plant Species Diversity and
Abundance Affects the Number of Arthropod Pests in Residential Landscapes
Michael J. Raup, Paula M. Shrewsbury, John J. Holmes, and John A.
Davidson
Abstract. An analysis of data collected from 212 residential
landscapes in suburban Maryland, U.S., revealed significant positive relationships
between the number of insect and mite pests in the landscape and the total
number of plants and plant species at the site. The number of pests in
a landscape increased very little in relation to the number of plants found
in the landscape. However, the number of arthropod pests increased at a
much greater rate as more species of plants were added. Two explanations
for these results are likely. Relatively few plants harbored arthropod
pests throughout the course of the season. Adding more plants of the same
species had little effect on altering the number of pest species in a landscape.
Arthropod pests tend to be relatively specialized in their host range.
When different species of plants are added to a landscape, more opportunities
are created for specialized insects and mites to colonize the site and
increase the richness of the arthropod fauna. When used in conjunction
with previous investigations involving monitoring approaches, these results
help IPM and PHC monitors plan and conduct site inspections more efficiently
and effectively.