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Contents: Selected Papers from the Research Symposium on Urban Greening and Landscape Architecture, held in Copenhagen, Denmark, June 1999.
EFFECTS OF ROAD DISTANCE AND
PROTECTIVE MEASURES ON DEICING NaCl DEPOSITION AND SOIL SOLUTION CHEMISTRY
IN PLANTED MEDIAN STRIPS
by Lars Bo Pedersen, Thomas B. Randrup, and Morten Ingerslev
Abstract. The deposition pattern of deicing salt and the resulting concentrations in the soil water were determined in planted median strips of two major approach roads with speed restrictions of 70 kmh (43.5 mph) in Copenhagen, Denmark. The objectives were to evaluate the effect of distance from the roadside and to test different straw mat protective measures. Deposition and soil water concentrations of sodium chloride (NaCl) decreased significantly within 2 m (6.6 ft) from the roadside compared to areas farther away. Straw mats mounted like a skirt around the tree stem did not constitute a proper protection against salt spray or splash and high salt concentrations in the soil water. In contrast, protection with straw mats on all sides of the trees resulted in a small but measurable effect. The highest concentrations of NaCl in the soil water were seen during the winter. However, there was a strong tendency of elevated concentrations persisting throughout the subsequent summer, which suggests that serious salt stress exists on the trees during the growing season. We concluded that planting at a distance of more than 2 m from the roadside is more effective than using straw mats in reducing the undesirable effects of salt spray deposition on trees as well as the salt concentration in the soil water.
HEALTH STATUS OF PLANE TREES (PLATANUS
SPP.) IN SPAIN
by M.L. Tello, C. Redondo, and E. Mateo-Sagasta
Abstract. The plane tree (Platanus spp.) is one of the most frequently used ornamental trees in Spanish urban areas. For the past 30 years, the health of urban tree plantings in various parts of the Iberian Peninsula has been observed and a number of diseases, common to the majority of them, detected. The most frequently occurring diseases that affect Platanus spp. are anthracnose (caused by the fungi Sporonema platani Blaüml.) and powdery mildew (caused by Microsphaera alni (DC.) Wint.), as well as diseases caused by other minor pathogens. Since 1997, we have focused our research on surveying the state of health of urban trees in the town of Aranjuez (Madrid), as an example of an urban location in central Spain. Within the numerous tree species that exist in the town, a serious problem was detected among plane trees. The symptoms observed (young shoots and branches up to 3 years old growing in whorls, necrotic tissue close to phloem and xylem, premature defoliation) indicate the possible existence of Gnomonia veneta (Sacc. et Speg.) Kleb, anamorph Sporonema platani Blaüml. The majority of the trees show these symptoms to one degree or another. Applying diagnostic and identification methods in the laboratory, we were able to demonstrate the presence of S. platani in all of the samples collected from symptomatic trees. A detailed description of the two main diseases, anthracnose and powdery mildew, in Spain is presented, with special reference to symptoms and dispersal under Spanish environmental conditions. A discussion about the most appropriate control methods is included.
GROWTH AND MORPHOLOGY DIFFER BETWEEN
WIND-EXPOSED FAMILIES OF SORBUS AUCUPARIA (L.)
by Arne Sæbø and Øystein Johnsen
Abstract. Rowan (Sorbus aucuparia), a small and decorative tree
with widespread distribution throughout Norway and Europe, is well suited
for growth on street verges, parks, and urban woodlands. With a better
knowledge of the genetic variation of its important traits, good genotypes
could be selected and the appearance of the trees thus improved. The objective
of this study was to describe the variation in growth, morphology, and
phenology of rowan between and within seed sources and at different wind
exposures. Seeds were collected from 10 to 15 trees within each of six
populations in a small area of 1,300 km2 (500 mi2)
along the southwestern coast of Norway. Three populations were wind-exposed
and three were sheltered. From each of the 78 mother trees included, 30
half-siblings were planted in the field at the Særheim Research Centre
(58.8°N, 5.5°E). Height growth, stem diameter, number of stems
and branches, branch angle, and growth start and termination were recorded
annually in five successive years. Large differences in most traits (estimated
heritabilities varied from 0.14 to 1.0) were found among families within
the stands. However, no important differences could be observed between
progenies from wind-exposed trees and those from sheltered trees, and differences
among stands were only minor. The results are discussed in relation to
the climatic adaptation of rowan and how this plant material can be used
in urban settings.
PRUNING TREES: THE PROBLEM OF
FORKS
by Christophe Drénou
Abstract. The term "fork" in a tree describes an axis that gives rise
to two or more equivalent axes, which together form sharp angles. Forks
can appear on the trunk or on the branches at various times in the life
of a tree. A fork on a trunk during formation is a potential defect likely
to ruin the straightness of the tree, reduce the length of the trunk, and
lead to enclosed bark. For these reasons, it is generally advisable to
eliminate forks and straighten large branches by formation pruning. Not
all tree forks are alike; some require intervention, but others are reabsorbed
on their own. We propose classifying forks into four major categories:
temporary forks, recurrent forks, main forks, and accidental forks. Each
category is the subject of a morphological description, an analysis of
the causes of forking, a prediction of the length of life of the forks,
and a discussion on the advisability of formation pruning.
TREE CROWN STABILIZATION WITH
THE DOUBLE-BELT SYSTEM OSNABRUCK
by Horst Stobbe, Dirk Dujesiefken, and Klaus Schröder
Abstract. Breaking-off of crown parts and large branches is a common
type of tree failure and can result in substantial damage to objects and
persons. The trees are often irreversibly damaged as well. Reasons for
this type of failure are usually included bark in forks and decay or cracks
in branches. As an alternative to topping or felling hazard trees, a tree
crown stabilization system was developed for the protection of crowns endangered
by possible failure. The System Osnabrück consists of at least two
double belts, each strapped around the stem or branch and connected by
wire cables. Wood-biological investigations on beech trees with six-year-old
double-belt systems showed that neither discoloration nor fungal attack
occurred in the wood and bark under the belts. The cambium beneath the
belts apparently was not impaired either. The double-belt system makes
it possible to maintain old trees with severe defects in urban areas by
safeguarding their natural crown architecture as well as providing maximum
safety to the public.
MARYLAND'S FOREST CONSERVATION
ACT: A PROCESS FOR URBAN GREENSPACE PROTECTION DURING THE DEVELOPMENT PROCESS
by Michael F. Galvin, Becky Wilson, and Marian Honeczy
Abstract. The Maryland Forest Conservation Act (FCA) was passed in 1991
to protect the state’s forest resources during development. Compliance
is required for any project for which grading is required on a unit of
land 40,000 ft2 (0.42 ha) or greater. Applicants must generate and submit
two documents. The first, a forest stand delineation (FSD), must identify
forest stands, specimen trees, and sensitive areas such as steep slopes,
hydric or erodible soils, critical habitat areas, streams, and floodplains.
This map is used to direct the location of the impacts away from priority
areas onsite. The second, a forest conservation plan (FCP), follows a priority
sequence concerning impacts to and retention of priority areas identified
in the FSD. Thresholds for clearing, afforestation, and reforestation are
established based on the net tract area, land-use category, existing forest
cover, and proposed clearing area. Forest and tree protective measures
are required for stand edges and specimen trees. Long-term protective instruments
are required to ensure that the retained area will remain forested. In
its first five years, FCA has been responsible for the retention of more
than 22,000 ac (10,000 ha) of forest, and 120% more forest retained and
planted than has been cleared for development.