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.
The Influence of Compaction
and Soil Strength on the Establishment of Four Australian Landscape Trees
Karen D. Smith, Peter B. May, and Gregory M. Moore
Abstract. An experiment was conducted to test the ability of
recently planted trees to grow new roots under waterlogged conditions and
to recover from waterlogging. Corymbia maculata (spotted gum, syn.
Eucalyptus maculata), Lophostemon confertus (brush box),
Platanus orientalis (oriental plane), and Platanus x acerifolia
(London plane) were subjected to a period of waterlogging and then to a
recovery phase after waterlogging had ceased. Root length was measured
at the end of both the waterlogging and recovery phases. The species were
found to vary considerably in their ability to tolerate and recover from
a period of waterlogging. Waterlogging suppressed root and shoot growth
in all experimental species. Young spotted gum and oriental plane were
able to initiate new roots under waterlogged conditions but London plane
and brush box were not.
Carbon Storage by Utility-Compatible
Trees
Andra' D. Johnson and Henry D. Gerhold
Abstract. Urban trees can favorably affect factors underlying
global warming by storing carbon and by reducing energy needed for cooling
and heating buildings. To estimate the amount of carbon stored by smaller
types of urban trees, excluding leaves and roots, standardized measurements
were taken to determine wood density, wood volume, and dry weight of selected
samples of Amelanchier, Malus, Pyrus calleryana,and Syringa reticulata
cultivars. Wood density as defined by specific weight ranged from 0.53
to 0.64 g/cm3 for all genera. Densities at two upper trunk positions
were significantly different from those at the base. The wood density of
Syringa reticulata was significantly less than the other genera.
Regression analyses of wood weight based on height and diameter of trees
up to 12 cm (4.7 in.) dbh indicated a linear relationship in Amelanchier,
but curvilinear (not linear) equations explained more of the variation
in Malus and Pyrus. Smaller trees, those 2.3 to 4.9 cm dbh,
typically stored between 2.1 and 2.3 kg of carbon in trunks and branches;
trees between 5.0 and 7.9 cm stored between 8.4 and 15.1 kg, and trees
larger than 8.0 cm up to 11.7 cm stored between 24.5 and 37.5 kg of carbon.
The narrow-crowned Pyrus calleryana ‘Capital’ stored considerably
lower amounts of carbon than the other Pyrus calleryana cultivars.
These estimates may be increased by 22% to add carbon stored in roots,
according to other studies.
Effect of Basement Sump Pump Effluent
on the Growth and Physiology of Urban Black Ash and Green Ash Ornamental
Trees
Cameron G. Lait, Suomal Saelim, Janusz J. Zwiazek, and Yao Zheng
Abstract. The effect of basement sump pump effluent discharge
in proximity to boulevards and ornamental trees was studied at several
sites near Edmonton, Alberta, Canada, throughout the summer of 1996. The
growth, leaf petiole water potentials, and gas exchange of black ash (Fraxinus
nigra) and green ash (F. pennsylvanica) trees were measured
at sites with and without nearby sump pump effluent discharge. Black ash
trees had higher mortality, altered water relations, and significantly
lower caliper increase at the site with sump pump effluent discharge compared
to trees at the site without effluent discharge. Green ash trees situated
away from sump pump effluent discharge had significantly greater caliper
increase than trees situated near effluent discharge. Furthermore, salt
injury symptoms were observed on both species of trees located at sites
with nearby effluent discharge. Our results demonstrate the importance
of monitoring sump pump effluent discharge and its effects on boulevard
ornamental trees in areas where soils are poorly drained or contain high
levels of salts. It is recommended that basement sump pump effluent discharge
hoses should be positioned away from boulevards and ornamental trees.
Comparing Forumulae That Assess
Strength Loss Due to Decay in Trees
Brian Kane, Dennis Ryan, and David V. Bloniarz
Abstract. Hazard trees are a concern for anyone who manages trees in a landscape setting, including arborists, urban foresters, and grounds managers. Through research, experience, observation, and common sense, arborists and urban foresters have identified many risk factors that predispose trees to failure. They have also developed thresholds to help determine the degree of hazard and whether a tree is in imminent danger of failing or needs annual (or more frequent) inspections. Two critical factors are involved in strength loss assessment in tree stems with defects. First, it is important to know how much strength is lost due to a defect such as a hollow or cavity. Second, the load required to cause failure needs to be considered since the wood of some trees is inherently stronger than others. Research currently underway at the University of Massachusetts, U.S., intends to test the strength loss due to decay in tree stems. Eventually, once the methodology has been refined, other tree structural defects will also be tested. A need for such research exists because hazard trees pose an important liability issue and because relatively little quantitative testing has been done to establish thresholds to classify trees as hazardous.
Four-Year Evaluation of Five Cultivars
of Pyrus calleryana
John E. Kuser, Gary Robinson, and Nicholas Polanin
Abstract. In November 1995, five cultivars of Callery pear (Pyrus calleryana: ‘Aristocrat’, ‘Capital’, ‘Chanticleer’, ‘Redspire’, and ‘Whitehouse’) were planted within parking-lot traffic islands at Livingston College, a Piscataway campus of Rutgers, The State University of New Jersey, U.S. During the next four years, the trees were observed each spring from bud break to flowering, and again each fall. Measurements of growth patterns as well as observational attributes of the cultivars were recorded. ‘Aristocrat’ flushed growth a few days earlier than the others, occasionally suffering frost damage to flowers. Its vertical growth was slower when compared to the other cultivars, with a wider branch angle, a distinctly lower, broader crown, and a deep purple-red fall color in contrast to the orange-reds of the other cultivars. ‘Aristocrat’ was the only cultivar in the study to display branch angle attachments necessary for storm resistance and growth success. ‘Chanticleer’ grew the fastest of the five and had the narrowest branch angles. ‘Redspire’ was intermediate in growth, somewhat open, with fairly narrow branch angles. ‘Capital’ and ‘Whitehouse’ were comparatively dense and heavy blooming; it was difficult to distinguish between them.
Biology and Management of the
Horned Oak Gall Wasp on Pin Oak
Eileen A. Eliason and Daniel A. Potter
Abstract. The horned oak gall wasp (Callirhytis cornigera)
induces large, woody galls on twigs of oak; these galls can disfigure trees
and result in extensive branch dieback. This paper reviews our recent research
on the pest’s biology and management on cultivated pin oaks (Quercus
palustris) in Lexington, Kentucky, U.S., especially aspects that are
of greatest relevance to tree care professionals. The gall wasp has alternating
agamic (all female) and sexual generations that develop, respectively,
in multi-chambered twig galls and single-chambered leaf galls along veins.
Wasp development required about 33 months in twig galls and about 3 months
in leaf galls. The number of gall wasps developing within twig galls ranged
from 1 to 160, and was dependent on gall size. Numerous other insects,
including parasitoids and inquilines, were found within the galls. Natural
enemies accounted for high mortality of C. cornigera, especially
in the leaf-galling generation where 70% to 80% of the larvae were parasitized.
The dogwood borer (Synanthedon scitula) infested about 15% of the
succulent 2- to 3-year-old twig galls. Adult S. scitula moths had
a similar, bimodal emergence period regardless of whether they originated
from dogwoods or horned oak galls. Insecticidal controls targeting the
leaf galling stage of C. cornigera killed the pest, but also its
parasitoids. Therefore, no reduction in the number of twig stem galls was
achieved. Difficulties in managing this pest in outbreak situations are
discussed.