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Irrigation Volume and Frequency and
Tree Size Affect Establishment Rate
by Edward F. Gilman, Robert J. Black, and Bijan Dehgan
Abstract. Irrigation volume had no effect on post-transplant
trunk diameter growth, crown spread, height growth, or stem xylem potential
of Quercus virginiana (live oak) in the first 27 months after transplanting.
Container-grown trees irrigated infrequently after transplanting grew more
slowly than those irrigated frequently and more slowly than field-grown
trees. This resulted from increased water stress on container trees that
were infrequently irrigated. Post-transplant growth of trees from a field
nursery was not affected by irrigation frequency. Three of 30 trees on
the infrequent irrigation schedule, which were transplanted from containers,
died the 1st time irrigation was cut back from twice each week to once
a week 7 weeks after transplanting, and new, nonlignified shoot and leaf
tissue on most other container trees dried up. No trees transplanted from
the field nursery died, nor did new growth wither. The 1st year after transplanting,
trunk diameters of trees collected from the wild increased more slowly
than those of trees transplanted from containers or from the field. However,
growth of trees from containers increased more slowly than for trees from
the other 2 production methods during the 2nd and 3rd year after transplanting.
During the first 27 months after transplanting, trunk diameter and tree
height increased faster on small-sized nursery trees of live oak than on
large-sized trees. Rate of trunk diameter growth for container trees slowed
the 2nd growing season on large-sized container trees, perhaps because
roots were not fully established in landscape soil. Frequently irrigated
trees established more quickly than those receiving infrequent irrigation.
Tree Growth Regulators: Issues of
Control, Matters of Management
by Gregory M. Moore
Abstract. All aspects of tree growth and development are regulated
by plant hormones and other growth-regulating substances. The most common
of these compounds are the auxins, gibberellins, and cytokinins, but other
substances such as ethylene and abscisic acid also have a significant impact
on tree biology. Usually there is a complex interaction between the growth
regulators to affect physiological responses. An understanding of plant
growth regulators can significantly increase the capacity of arborists
to effectively manage trees in urban landscapes. However, to effectively
use plant growth regulators as a tool for tree management, arborists must
understand the subtlety of their interactions. Furthermore, to achieve
arboricultural objectives, arborists must also understand the nature of
the biochemistry and importance of precise and targeted application of
plant growth regulators. In an era of modern arboriculture practice, tree
hormones and growth regulators are not just substances of control but tools
of effective tree management.
The Influence of Sodium Chloride
and Waterlogging Stresses on Alnus Cordata
Glynn C. Percival, Martin P. Biggs, and Geoffrey R. Dixon
Abstract. Sodium chloride solutions were applied as a root drench
to containerized Alnus cordata trees grown in freely drained or waterlogged
compost substrates. Leaf chlorophyll fluorescence; cell electrolyte leakage;
plant mortality; leaf necrosis; time to bud burst; and leaf, shoot, and
root macronutrient concentrations were evaluated. Waterlogging using distilled
water caused no significant stress compared to controls, apart from increasing
root iron and manganese concentrations. Complete mortality was recorded
in trees watered with a sodium chloride solution 4.5% or waterlogged in
sodium chloride solutions 2%. Watering or waterlogging with distilled water
had no significant effect on mortality, while 66.6% of trees watered with
a 2% sodium chloride solution died. Applications of sodium chloride tended
to increase time to bud burst compared to controls. Irrespective of whether
trees were grown in freely drained or waterlogged compost, applications
of sodium chloride to roots decreased leaf chlorophyll fluorescence and
increased cell electrolyte leakage and leaf necrosis for up to 15 days
after bud burst. Significant reductions in chlorophyll fluorescence was
detected by day 3 following bud burst; however, significant increases in
cell electrolyte leakage and leaf necrosis were not detected until day
6. Applications of sodium chloride significantly increased sodium and chloride
concentrations in root, leaf, and shoots irrespective of drainage, with
higher concentrations reflecting applications of stronger salt solutions.
Calcium, phosphorous, magnesium, and potassium concentrations in cell tissues
were unaffected by treatments. Depressed leaf and shoot copper, zinc, and
iron concentrations were recorded in trees waterlogged in sodium chloride
solutions 4.5%. Irrespective of treatment, no significant effects on manganese
concentrations of leaf and shoot tissue were found, but significantly lower
concentrations of manganese were recorded in roots. Greater reductions
generally reflected stronger applicationof sodium chloride.
Cytospora Canker Development
on Aspen in Response to Nitrogen Fertilization
Response to Nitrogen Fertilization by
Abstract. The effect of nitrogen fertilization on Cytospora canker
development in aspen (Populus tremuloides) was examined in a greenhouse
hydroponic system. Aspen trees grown in rock wool or sand were watered
with 1 of 5 nitrogen treatments: 0, 55, 111, 185, or 333 mg/L nitrogen
as (NH4)2NO3. After 6 wk, trees were inoculated with 2 isolates of Cytospora
chrysosperma in separate wounds. Canker length and width were measured
every 2 wk for 6 wk, beginning the 2nd week after inoculation. To assess
the effect of prolonged nutrient treatment on canker development, a subset
of the original trees was selected to receive treatments for 2 growing
seasons, with inoculations at 6 wk after treatments were begun in the 2nd
season. Nitrogen deficiency (0 mg/L) contributed to significantly larger
cankers in 1 of 4 trials run for 1 growing season and in the 2 trials carried
out for 2 growing seasons (P = 0.000.006). Canker sizes on trees treated
with the other nitrogen rates were not significantly different from each
other. Large cankers formed on trees treated with the abnormally high rate
(333 ppm), but the differences were not significant from the other nitrogen
treatments. Thus, nitrogen deficiencies increase the likelihood of canker
expansion, while proper nutrient management allows aspen to defend against
canker expansion induced by Cytospora fungi.
A Survey of Licensed Tree Experts
in Maryland
by Michael F. Galvin and Peter J. Becker
Abstract. In Maryland, persons engaged in the work of the treatment
and care of trees for compensation must be licensed by the Department of
Natural Resources. The Department of Natural Resources—Forest Service,
the Mid-Atlantic Chapter of the International Society of Arboriculture,
the Maryland Arborist Association, and the Maryland Community Forest Council
cosponsored a survey of Licensed Tree Experts (LTEs). The survey's purposes
were to estimate the total number of jobs and gross dollar revenue that
the arboricultural industry provides to the state of Maryland; to identify
the tree care industry as a constituency in the business community; to
identify training resources and trade affiliations most used by LTEs; to
identify business type, geographic concentration, and client type; and
to provide input into agency regulations affecting the industry. It is
estimated that the tree care industry in Maryland employs 2,841 individuals
and generates more than $134.5 million in annual gross revenue.
Resident Involvement in Inspecting
Trees for Dutch Elm Disease
by Dawn K. Nanini, Robert Sommer, and Lawrence S. Meyers
Abstract. This study investigated the costs and benefits of a
public-private partnership in the monitoring of mature elm trees threatened
by Dutch elm disease (Ceratocystis ulmi). To compensate for a budget shortfall,
the Sacramento Tree Foundation began its Save The Elms Program (STEP),
which enlisted the help of volunteers for the early detection of Dutch
elm disease. Of the 269 residents who initially expressed interest in the
program, only half received training due to scheduling difficulties and
time constraints. A mail survey compared the knowledge and attitudes of
trained volunteers and those who volunteered but did not receive training.
While all respondents endorsed the importance of street trees to the area,
those with training were more knowledgeable about their local urban forest
and were more satisfied with their neighborhoods.
Tree Growth After Trenching
and Compensatory Crown Pruning
by Gary W. Watson
Abstract. The roots of pin oak (Quercus palustris) trees were severed by trenching on 1, 2, or 3 sides the tree. The distance between the trunk and the trenches was approximately equal to the trunk circumference. Half of the trees also received compensatory crown pruning. All trees survived and significant dieback was noted only on trees that were trenched on 3 sides. Generally, the more extensive the trenching, the greater the growth reduction and dieback, and the longer the reduction persisted. Compensatory pruning increased twig growth for all trenching treatments, but seems to be most beneficial in reducing dieback after severe root loss from trenching. Under certain circumstances and in the absence of other construction impacts, vigorous trees may be able to tolerate and recover from trenching in the root zone.