Trees can live for a long time but eventually die, either from natural causes or killed by man. Ill-health of trees can be diagnosed, and early treatment, pruning or felling to prevent the spread may result in timber stocks and amenity trees being saved. Tree owners and Arborists/arboriculturists need to be aware of the risk posed by hazardous trees. Construction projects sometimes avoidably damage trees.
The causes of tree damage and abnormalities can conveniently be divided into either biotic (from living sources) or abiotic (from non-living sources). [1]
Biotic sources include insects (e.g. that bore into the tree), mammals (e.g. deer that rub bark off), fungi, birds, nematodes, bacteria and viroids. [2]
Abiotic sources include lightning, vehicles impacts, construction activities, drought, waterlogging, frost, winds, chemicals in the soil and air and soil nutrient deficiencies. Construction activities can involve any of a number of damage types, including grade changes or compaction that prevent aeration to roots, spills involving toxic chemicals such as cement or petroleum products, or severing of branches or roots. Trees with thinner bark such as birch and American sycamore are more sensitive to such damage. [3]
One of the most common naturally occurring hazards in large trees is weakness in the union between trunk and branch (or between co-dominant substems). V-shaped unions may create weakness and increase failure risk; in some situations this can be reduced by tree cabling, which limits how far the union can flex in strong winds or other loads.[ citation needed ].
Any of these damage sources and the natural ageing of trees may result in trees or parts of them failing prematurely. The term "hazard trees" is commonly used by arborists/arboriculturists, and industry groups such as power line operators, for trees that, due to disease or other factors, are more susceptible to falling in windstorms, or having parts of the tree fall. Damage may also disfigure amenity trees, create unacceptable risks to people, reduce the safe useful life of trees or reduce the value of commercial timber.[ citation needed ]
Trees can withstand large amounts of some types of damage and survive, but even small amounts of other traumas can result in death, disfiguration or hazards.[ citation needed ] Established trees will normally not tolerate any appreciable disturbance of the root system. [4] Without arboricultural advice, lay people and construction professionals may not be aware how easily or indirectly a tree can be killed.[ citation needed ]
Fallen logs of white spruce and trembling aspen at various stages of decomposition were sampled from undisturbed and 1, 14, and 28-year-old post-fire and post-harvest sites in northern Alberta, and studied for differences in the associated microfungus communities (Lumley et al. 2001). [5] Wood samples were plated directly onto each of 6 different media and from these fungal species were identified and enumerated over a 24-month period. Approximately 10 000 isolates were obtained, representing 292 species of filamentous microfungi, including 41 ascomycetes, 29 zygomycetes, and 222 mitosporic fungi. The most commonly isolated species were Trichoderma viride, Rhinocladiella atrovirens, Penicillium pinophilum and Mortierella ramanniana. Cluster analysis and ordination of microfungus communities in logs showed that the tree species of the log had the greatest influence on the species composition of communities. Fungus community composition was also correlated with the stage of decomposition. Species richness was highest in logs from undisturbed sites, and lowest in logs from the most recently disturbed sites. Species diversity (Shannon-Weaver) was only slightly higher at undisturbed sites than at disturbed sites. The most significant environmental factor was log moisture, which increased proportionately with stage of decomposition and was significantly correlated with climatic factors.[ citation needed ]
Wounds inflicted on residual trees during partial cutting often provide portals for decay fungi. Affected trees are prone to blowdown and breakage at the wound site, and even if they survive to rotation age their value is reduced by staining and decay in the wood. The influence of temperature on microbial diversity in wounds in white and black spruces was investigated by Dumas and McLaughlin (2003). [6] Samples were taken from trees wounded during manual or feller-buncher partial cutting and skidding operations in the Black Sturgeon Forest, 120 km northeast of Thunder Bay, Ontario. The samples were taken from 76 trees in early October when the mean aerial temperature exceeded 0 °C and 23 trees in late October/early November when the mean aerial temperature was below 0 °C, to serve as the pre-freeze-up and post-freeze-up groups, respectively. The wounds were sampled and cultured. The number and ratio of bacteria, actinomycetes, and fungi on one-week-old wounds varied between pre- and post- freeze-up wounds, wound locations, and media. However, random samples of the different classes of microbes isolated from the 2 spruce species did not differ significantly, indicating no relationship between tree species and microbe. Wounds were more common on stems (94) than on roots (64) or butts (33). Wounds on roots averaged 2 and 3 times the area of those on stems and butts, respectively. More bacteria than fungi were isolated from the pre-freeze-up wounds than from the post-freeze-up wounds, while fungi were more plentiful than bacteria on the post freeze-up wounds.[ citation needed ]
Evaluating the danger a tree presents, whether by its state of health or by its situation, to people and/or property is called Tree Risk Assessment. Techniques have emerged based on Matheny & Clark's [7] matrix of three factors which contribute to the degree of risk namely (i) failure potential (ii) size of defective part and (iii) target rating (how often something or someone is present to be harmed or damaged). Subsequently, a Quantified Tree Risk Assessment ("QTRA") system has been developed by others that calculates the risk numerically with reference to cost implications of tree damage and published societal norms of acceptable, tolerable and unacceptable risk. [8] The International Society of Arboriculture updated its approach in 2012 with a qualitative (words based) matrix known as Qualitative Tree Risk Assessment ("TRAQ") [9]
To comply with the tree owner's legal duty of care to occupiers, visitors, passers-by or neighbours, where regular observation or monitoring of the tree's condition is not possible, tree inspections should be carried out at appropriate intervals by a competent person and their risk reduction recommendations should be implemented. [10]
Plant Health Care (PHC) is multi-dimensional management strategy for tree and plant care to preserve the vitality of the urban and community forest. [11] Arborists and Plant Health Care Specialists apply a broad range of techniques by selecting and integrating treatment options that protect and enhance the health, structure, and appearance of plants in the landscape. [11] [12]
"PHC attempts to prevent problems before they start." [12] It is a holistic approach to plant management that focuses on a plant's interaction between living and nonliving components of the landscape. Typically, PHC is a service business that relies on the relationship between arborist and client to make management decisions based on the health of the tree, the goals of the client, and the professional education and recommendation provided by the arborist. [11] [12]
While PHC evolved from Integrated Pest Management (IPM), the goals and emphasis of each system vary. PHC focuses on managing the specific, individualized needs of a plant and its surrounding growing environment. [12] PHC involves identifying what stressors are impacting a plant or tree's health to create a care profile that reflects the clients goals to maintain healthy plants and trees within an environmental context.
Assessment of the damaging effect of construction activities on a tree can be based on three factors: severity, extent and duration. Fundamentally activity should avoid the crown of the tree and the volume of rooting required by the tree for ongoing vitality.[ citation needed ] Severity is related to the degree of intrusion into the rooting area and resultant root loss. Extent is related to a percentage of a factor such as canopy, roots or bark,[ clarification needed ] and duration is based on the length of time that the activity interferes with the tree's normal functions.
Various organizations, such as the International Society of Arboriculture, the British Standards Institute [13] and the Tree Industry Association (formerly the National Arborist Association), have long recognized the sensitivity of tree health to construction activities. The effects are important because they can result in monetary and/or amenity value losses due to tree damage and resultant remediation or replacement costs, and/or prosecution for violation of government ordinances (in the UK, planning laws, regulations and policies) or community- or subdivision restrictions.[ citation needed ]
In the US, protocols for tree management prior to, during and after construction activities are well established, tested and refined. These basic steps are involved:[ citation needed ]
In the UK, a similar protocol exists. [14]
Arboriculture is the cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants. The science of arboriculture studies how these plants grow and respond to cultural practices and to their environment. The practice of arboriculture includes cultural techniques such as selection, planting, training, fertilization, pest and pathogen control, pruning, shaping, and removal.
An arborist, or arboriculturist, is a professional in the practice of arboriculture, which is the cultivation, management, and study of individual trees, shrubs, vines, and other perennial woody plants in dendrology and horticulture.
Integrated pest management (IPM), also known as integrated pest control (IPC) that integrates both chemical and non-chemical practices for economic control of pests. The UN's Food and Agriculture Organization defines IPM as "the careful consideration of all available pest control techniques and subsequent integration of appropriate measures that discourage the development of pest populations and keep pesticides and other interventions to levels that are economically justified and reduce or minimize risks to human health and the environment. IPM emphasizes the growth of a healthy crop with the least possible disruption to agro-ecosystems and encourages natural pest control mechanisms." Entomologists and ecologists have urged the adoption of IPM pest control since the 1970s. IPM is a safer pest control framework than reliance on the use of chemical pesticides, mitigating risks such as: insecticide-induced resurgence, pesticide resistance and (especially food) crop residues.
Pruning is a horticultural, arboricultural, and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds, or roots.
Urban forestry is the care and management of single trees and tree populations in urban settings for the purpose of improving the urban environment. Urban forestry involves both planning and management, including the programming of care and maintenance operations of the urban forest. Urban forestry advocates the role of trees as a critical part of the urban infrastructure. Urban foresters plant and maintain trees, support appropriate tree and forest preservation, conduct research and promote the many benefits trees provide. Urban forestry is practiced by municipal and commercial arborists, municipal and utility foresters, environmental policymakers, city planners, consultants, educators, researchers and community activists.
Oak wilt is a fungal disease caused by the organism Bretziella fagacearum that threatens Quercus spp. The disease is limited to the eastern half of the United States; first described in the 1940s in the Upper Mississippi River Valley. The pathogen penetrates xylem tissue, preventing water transport and causing disease symptoms. Symptoms generally consist of leaf discoloration, wilt, defoliation, and death. The disease is dispersed by insect vectors and to adjacent trees through underground root networks. However, human spread is the most consequential dispersal method. Moving firewood long distances can potentially transport diseases and invasive species.
Girdling, also called ring-barking, is the circumferential removal or injury of the bark of a branch or trunk of a woody plant. Girdling prevents the tree from sending nutrients from its foliage to its roots, resulting in the death of the tree over time, and can also prevent flow of nutrients in the other direction depending on how much of the xylem is removed. A branch completely girdled will fail and when the main trunk of a tree is girdled, the entire tree will die, if it cannot regrow from above to bridge the wound. Human practices of girdling include forestry, horticulture, and vandalism. Foresters use the practice of girdling to thin forests. Extensive cankers caused by certain fungi, bacteria or viruses can girdle a trunk or limb. Animals such as rodents will girdle trees by feeding on outer bark, often during winter under snow. Girdling can also be caused by herbivorous mammals feeding on plant bark and by birds and insects, both of which can effectively girdle a tree by boring rows of adjacent holes.
Environmental hazards are those hazards that affect biomes or ecosystems. Well known examples include oil spills, water pollution, slash and burn deforestation, air pollution, ground fissures, and build-up of atmospheric carbon dioxide. Physical exposure to environmental hazards is usually involuntary
In trees, heart rot is a fungal disease that causes the decay of wood at the center of the trunk and branches. Fungi enter the tree through wounds in the bark and decay the heartwood. The diseased heartwood softens, making trees structurally weaker and prone to breakage. Heart rot is a major factor in the economics of logging and the natural growth dynamic of many older forests. Heart rot is prevalent throughout the world affecting all hardwood trees and can be very difficult to prevent. A good indication of heart rot is the presence of mushrooms or fungus conks on the tree.
Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity, agricultural chemicals or improper disposal of waste. The most common chemicals involved are petroleum hydrocarbons, polynuclear aromatic hydrocarbons, solvents, pesticides, lead, and other heavy metals. Contamination is correlated with the degree of industrialization and intensity of chemical substance. The concern over soil contamination stems primarily from health risks, from direct contact with the contaminated soil, vapour from the contaminants, or from secondary contamination of water supplies within and underlying the soil. Mapping of contaminated soil sites and the resulting clean ups are time-consuming and expensive tasks, and require expertise in geology, hydrology, chemistry, computer modelling, and GIS in Environmental Contamination, as well as an appreciation of the history of industrial chemistry.
Tree topping is the practice of removing whole tops of trees or large branches and/or trunks from the tops of trees, leaving stubs or lateral branches that are too small to assume the role of a terminal leader. Other common names for the practice include hat-racking, heading, rounding over, and tipping. Some species of trees are more likely to recover from topping than others. There are alternatives to topping that can help to achieve the same goals without damaging trees.
The Certified Arborist credential identifies professional arborists who have a minimum of three years' full-time experience working in the professional tree care industry and who have passed an examination covering facets of arboriculture. The Western Chapter of the International Society of Arboriculture (ISA) started the certification program in the 1980s, with the ISA initiating it in 1992.
Indoor mold or indoor mould, also sometimes referred to as mildew, is a fungal growth that develops on wet materials in interior spaces. Mold is a natural part of the environment and plays an important part in nature by breaking down dead organic matter such as fallen leaves and dead trees; indoors, mold growth should be avoided. Mold reproduces by means of tiny spores. The spores are like seeds, but invisible to the naked eye, that float through the air and deposit on surfaces. When the temperature, moisture, and available nutrient conditions are correct, the spores can form into new mold colonies where they are deposited. There are many types of mold, but all require moisture and a food source for growth.
Soil solarization is a non-chemical environmentally friendly method for controlling pests using solar power to increase the soil temperature to levels at which many soil-borne plant pathogens will be killed or greatly weakened. Soil solarization is used in warm climates on a relatively small scale in gardens and organic farms. Soil solarization weakens and kills fungi, bacteria, nematodes, and insect and mite pests along with weeds in the soil by mulching the soil and covering it with a tarp, usually with a transparent polyethylene cover to trap solar energy. This energy causes physical, chemical, and biological changes in the soil community. Soil solarization is dependent upon time, temperature, and soil moisture. It may also be described as methods of decontaminating soil or creating suppressive soils by the use of sunlight.
Forest pathology is the research of both biotic and abiotic maladies affecting the health of a forest ecosystem, primarily fungal pathogens and their insect vectors. It is a subfield of forestry and plant pathology.
The Master Arborist or Board Certified Master Arborist credential identifies professional arborists who have attained the highest level of arboriculture offered by the International Society of Arboriculture (ISA) and one of the two top levels in the field. There are several paths to the Board Certified Master Arborist, but typically on average each has been an ISA Certified Arborist a minimum of three to five years before qualifying for the exam. The certification began as a result of the need to distinguish the top few arborists and allow others to identify those with superior credentials. The ISA added specialty certifications of Utility Specialist, for those maintaining vegetation around electric utility wires, Municipal Specialist, for those with additional experience managing public urban trees.
Hylastes ater is a species of beetle in the family Curculionidae, the true weevils. It is a bark beetle, a member of the subfamily Scolytinae. Its common name is the black pine bark beetle. It is native to Europe and parts of Asia, including China and Korea. It is known as an introduced species in many other regions, including Australia, New Zealand, the Americas, and South Africa. It is a pest of pines and other trees, and it is widespread in areas where pine trees are cultivated. The species "is an important threat to the biosecurity of all forested countries."
Integrated pest management in museums, libraries, archives and private collections is the practice of monitoring and managing pest and environmental information with pest control methods to prevent pest damage to collections and cultural property. Preserving cultural property is the ultimate goal for these institutions. The pests come in many different forms: insects, mites, rodents, bats, birds, and fungi and the two most common types are insects and fungi. It is widely recommended that every museum have some form of pest control in place and monitoring system to protect their collection and that museums review their storage and museum facilities to determine how to best control and prevent pest infestations while utilizing an Integrated Pest Management plan.
A branch attachment is where a branch is attached to the trunk of a tree. Three types of branch attachment are recognized due to differences in the anatomical position of buds that form them. Two key components contribute to the mechanical strength and toughness of the attachment: interlocking wood grain at the top of the attachment and an embedded knot that often lies within the attachment. A common malformation of a branch attachment is the inclusion of bark within the join, which can weaken the attachment.
Tree care is the application of arboricultural methods like pruning, trimming, and felling/thinning in built environments. Road verge, greenways, backyard and park woody vegetation are at the center of attention for the tree care industry. Landscape architecture and urban forestry also set high demands on professional tree care. High safety standards against the dangers of tree care have helped the industry evolve. Especially felling in space-limited environments poses significant risks: the vicinity of power or telephone lines, insufficient protective gear and narrow felling zones with endangered nearby buildings, parking cars, etc.. The required equipment and experience usually transcends private means and is often considered too costly as a permanent part of the public infrastructure. In singular cases, traditional tools like handsaws may suffice, but large-scale tree care usually calls for heavy machinery like cranes, bucket trucks, harvesters, and woodchippers.
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