(參考資料：City Living Seattle
)GARDEN HOTLINE | When to call an arborist
Wet and windy: the classic Pacific Northwest winter day. Mild temperatures are great for overwintering less-hardy plants, but a string of 45-degree days followed by high winds and excessive rain can cause serious damage to trees. Extended periods of saturated or poorly draining soil can provide the perfect environment for fungi that affect foliage and roots.
Seattle is home to many large conifers and native deciduous trees like big-leaf maple and red alder that are now suffering as a result of weather, disease and urban development.
Hiring an arborist can be more costly than hiring a landscaper or doing the work yourself. How do you decide when is it time to call in an expert?
What is an arborist?
Arborists are knowledgeable about planting, caring for and maintaining individual trees. Those who are certified by the International Society of Arboriculture (ISA) have demonstrated knowledge of tree care through work experience and passed a comprehensive test developed by leading experts in their field.
ISA-certified arborists who meet the criteria can also complete extra training to become qualified in tree risk assessment. They are the authorities on tree health, safety and preservation and may even be called upon to provide expert testimony in disputes involving trees.
It can be difficult for an untrained person to judge when a tree is in trouble. A diseased tree may not show visible symptoms for a few years or more but may be weakened enough to be vulnerable during a storm. Weakened trees may also be more vulnerable to attack from pests.
Sometimes it is easier and cheaper to remove a tree than it is to bring it back to health through proper tree care techniques. Arborists consider removal a last resort but will make a recommendation to remove a tree if deemed necessary due to the potentials hazards it may pose.
A homeowner well-versed in proper pruning techniques and with a sharp set of pruning equipment may feel comfortable removing a broken branch from a 5-foot-high tree, but working on a conifer that towers 75 feet or more is a daunting and dangerous task.
Large broken or hanging limbs and uprooted or downed trees can react in unpredictable ways when cut. Special equipment and training is needed to safely complete the work. Make sure that the arborist you hire is insured, equipped and able to work on large or hazard trees.
Do not try to remove branches that are within 10 feet of a high-voltage electrical line. Call Seattle City Light, at (206) 386-1650, for help before you hire a professional. The utility will arrange to have the trees pruned to prevent branches from falling on the lines before any more work is done. Many private tree companies are not certified to do this type of work.
Services arborists provide
Homeowners and business professionals alike can benefit from the services arborists provide. Landscapers who are not also trained as arborists may not have the skills or equipment necessary to perform certain tasks correctly and safely.
Arborists are trained to handle complicated tree projects, in particular on large trees. Improper planting or choosing an inappropriate tree for the space can result in problems later, so be sure to hire an experienced landscaper or engage an arborist when choosing and planting trees in your garden.
If you need help with any of the following tree issues, consider calling an arborist:
•Selection and planting;
•Health care and maintenance (pruning, cabling and bracing, disease, pest, fruit production, soil and water);
•Disputes and negligence;
•Land planning; and
•Environmental impact of development.
Find an arborist
The Pacific Northwest Chapter of the International Society of Arboriculture has an online search directory for ISA-certified arborists in the Pacific Northwest: www.pnwisa.org/hire-an-arborist/isa-certified-arborist-directory.
Plant Amnesty provides referrals for arborists, arboricultural consultants, diagnosticians and professional gardeners in King County. For more information, go to www.plantamnesty.org/referral-services.
Seattle City Light has information available online for reporting a problem, as well as information about vegetation management and tree trimming in Seattle. Go to www.seattle.gov/light/vegmgmt/default.htm for links to questions about services the City of Seattle offers. Find “The Right “Tree,” a printable PDF with tips on plant selection and tree care at www.seattle.gov/light/printdocs/right_tree_book.pdf.
The Seattle Department of Transportation has information available about selection, planting and care of street trees at www.seattle.gov/transportation/treeplanting.htm.
To learn more about tree care and selection and to find arborist referrals, contact the Garden Hotline at (206) 633-0224 or www.gardenhotline.org.
SUE HARTMAN is an environmental educator for the Garden Hotline at Seattle Tilth (seattletilth.org).
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