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Tree Wound Reactions of Differently
Treated Boreholes
by Dirk Dujesiefken, Andreas Rhaesa, Dieter Eckstein, and Horst Stobbe
Abstract. Holes from increment borings create wounds that lead
to discoloration and may result in a colonization of the wood by fungi.
There are various opinions about the damage caused by such borings and
about the efficacy of wound dressings. For this reason, 78 differently
treated boreholes in large-leaved lime (Tilia platyphyllos Scop.)
and small-leaved lime (Tilia cordata Mill.), as well as in horsechestnut
(Aesculus hippocastanum L.) and silver birch (Betula pendula
Roth), were examined macroscopically and microscopically with regard to
the wound reactions nearly 10 years after boring. Obvious differences in
wound reactions were observed among the tree species. Both species of lime
compartmentalized the wounds very effectively. Horsechestnut, on the other
hand, revealed more extensive discoloration. Silver birch had the weakest
compartmentalization, with discoloration up to 2 m (6.6 ft) in length.
Cambial dieback around all borings, except for those plugged with creosote-impregnated
wood dowels, was approximately the same for all species. Fungi occurred
only within the discoloration. Cell wall disintegration was rarely observed.
Treatment with LacBalsam® or polyurethane had little or no influence
on the wound reactions. Boreholes sealed with impregnated wood dowels had
far-reaching discoloration and cambial dieback as a result of the toxic
effect of creosote.
A Methodology for Assessing and
Managing Biodiversity in Street Tree Populations: A Case Study
by Michael F. Galvin
Abstract. As a consequence of compacted soils, impervious surfaces,
heat irradiation, pollution, and other stresses, urban trees have an average
expected service life of 10 to 25 years. Most public agency budgets for
street tree replacement and maintenance are declining. Public tree managers
need tools to prolong the service life of street tree populations while
reducing the need for maintenance activities (including pruning and pest
management). Many jurisdictions rely on "approved tree" lists, but these
often contain large numbers of species generally unavailable in a given
area, and filters for diversity are seldom part of these documents. To
avoid catastrophic losses and pest outbreaks associated with virtual monocultures,
the Maryland Department of Natural Resources has developed a methodology
for assessing biodiversity in existing populations. An inventory is taken.
The results of the inventory are broken down taxonomically by family, genus,
and species; The results are then analyzed, with target levels established
as follows: no more than 30% of any one family, 20% of one genus, or 10%
of one species should be present. Based on the results of the assessment,
recommendations are made as a tool for use in future replacement contracts
to bring about the desired species composition.
Effects of Tree Cover on Parking
Lot Microclimate and Vehicle Emissions
by Klaus I. Scott, James R. Simpson, and E. Gregory McPherson
Abstract. A pilot study was performed to measure the difference
in parking lot microclimate resulting from the presence or absence of shade
tree cover. Microclimate data from contrasting shade regimes were then
used as input to a motor-vehicle emissions model. Model results were used
to estimate the potential for regional increases in parking lot tree cover
to reduce motor-vehicle hydrocarbon and nitrogen oxide (NOx) emissions.
Will Subterranean Termites Consume
Landscape Mulches?
by Mary L. Duryea, Jacob B. Huffman, R. Jeffery English, and Weste
Osbrink
Abstract. Subterranean termites live in colonies in the soil
in both temperate and tropical regions throughout the world. These termites
feed on cellulose and are a major cause of damage to wood in use. Organic
tree-based mulches provide many benefits to a landscape, yet recently,
questions about whether they could harbor or be a source of food for termite
colonies have arisen. In a series of 2 no-choice food experiments, this
study investigated whether termites would consume 6 landscape mulches:
cypress, eucalyptus, melaleuca, pine bark, pine straw, and a utility pruning
mulch, and 5 woods: pine sapwood, cypress heartwood and sapwood, and melaleuca
heartwood and sapwood. In the wood experiments, termites consumed pine
and cypress sapwood but did not consume the cypress heartwood or melaleuca
sapwood or heartwood. In the pine and cypress sapwood, 64% to 77% of the
termites survived, while melaleuca and cypress heartwood had fewer than
15% live termites.In Experiment 1, termites ate more of the utility mulch
than any other mulch. In Experiment 2, termites consumed all mulches except
melaleuca, which was the least desirable food in both experiments. Correlations
with chemical characteristics were significant for both nitrogen and phosphorus
(r = 0.91 and 0.96), showing that termites preferred mulches with higher
N and P concentrations.In both experiments termite consumption was also
correlated with 1-year decomposition of mulches in another study. Because
termites ate most mulches, further investigation is necessary to determine
whether landscape mulches around building foundations could harbor or support
termite colonies.
Progress in the Development
of Borer-Resistant White-Barked Birches
by Frank S. Santamour, Jr.
Abstract. This paper presents a thorough and comprehensive review
of the current state of knowledge regarding the hosts of the bronze birch
borer (Agrilus anxius) and biochemical and genetics studies designed
to identify and develop borer-resistant white-barked birches. Both older
and heretofore unpublished observations and experiments are evaluated to
provide a framework for future research. Based on the hypothesis that the
presence of the chemical rhododendrin in the inner bark of birches is the
key to their susceptibility to the borer, the finding that Betula nigra
and B.maximowicziana do not contain this compound, and that B.
davurica, B. occidentalis, and B. papyrifera have low
levels, increased experimentation with these species is encouraged. Some
low-rhododendrin, and potentially borer-resistant, hybrids have also been
discovered and are awaiting large-scale propagation for long-term trials.
Effect of Organic and Mineral
Mulches on Soil Properties and Growth of Fairview Flame® Red Maple
Trees
by Jeffery K. Iles and Michael S. Dosmann
Abstract. Five mineral mulches (crushed red brick, pea gravel,
lava rock, carmel rock, and river rock) and 3 organic mulches (finely screened
pine bark, pine wood chips, and shredded hardwood bark) were evaluated
over 2 years to determine their influence on soil temperature, moisture,
and pH, and to quantify their effect on growth of Fairview Flame® red
maple (Acer rubrum L.). Soil temperatures were highest and moisture
percentages lowest under the mineral mulches and nonmulched control. Soil
pH readings were highest under shredded bark and wood chips, and lowest
in the nonmulched control. Trees growing in river rock, crushed brick,
pea gravel, and carmel rock had larger stem calipers than those growing
in shredded bark plots. Crushed brick, pea gravel, and carmel rock treatments
also resulted in greater leaf dry mass than did shredded bark. These results,
however, should not be interpreted as an indictment of organic mulches.
Because stem caliper and leaf dry mass measurements of trees growing in
wood chips and any of the mineral mulches were not statistically different,
blanket statements and generalizations regarding the performance of woody
plants mulched with organic or mineral (rock) materials are unwise.
Feeding Preference for Selected
Tilia spp. and Cultivars by the Adult Japanese Beetle (Coleoptera:
Scarabaeidae)
by Fredric Miller and George Ware
Abstract. Species and hybrids of Tilia are widely used
in urban landscapes and as street trees. Planting Tilia species
that are less preferred by the Japanese beetle (Popillia japonica
Newman) would greatly minimize the need for insecticide sprays, which would
in turn reduce environmental contamination, human exposure, and management
costs. Thus, a study was initiated to evaluate horticulturally desirable
Tilia spp. for feeding preference by the adult Japanese beetle.
A secondary objective of the study was to determine if leaf pubescence
is a factor in feeding preference. The Asian species of T. petiolaris,
T. oliveri, T. chinensis, and T. japonica show promise for
partial resistance to Japanese beetle. Three North American species, T.
americana, T. heterophylla, and T. caroliniana, also
look promising along with the pubescent European species of T. tomentosa
and T. tomentosa 'Erecta.