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Caring for the Arboretum Trees and Plant CollectionsThe Arboretum's plantings constitute one of the premier woody plant collections in the United States with nearly 4400 different kinds of plants. These plantings are displayed among trees of our native Puget trough hemlock-cedar forest zone. The retention of native trees is part of WPA's naturalistic landscape style. This style also poses special challenges and needs in providing for the care of both native and collected plants. The maintenance and care of these plants is closely tied to our mission of education, conservation, and display. Both University and City staff work hard in caring for the Arboretum's landscape. Conservation of the plant collections in this highly utilized facility includes management for insect and disease pests, weak and dead plant removal, hazard reduction, plant replacement, and landscape restoration. The Arboretum employs a holistic approach to managing plant health problems, combining the use of carefully timed, least toxic control applications, cultural practices to improve plant vigor, and the removal of severely affected plants beyond restoration. Extensive monitoring and follow-up evaluations are a critical part of this work. Click here for more information about plant health care and the pest management program at the Arboretum. The arboriculture program covers care and management of collection and native trees. The goal is to reduce potential hazards through inspections and preventive work, as well as conserving the plant collections. This work includes pruning and training for young trees, cabling and bracing to preserve scaffold limbs in large trees, pruning and removal. The effects of root rot diseases as large trees age are a major contributor to hazards and actual failures in the larger native trees, particularly big-leaf maples Tree Care Program
The UW Botanic Gardens would like to thank Tree Solutions, Inc. for bringing the latest technology in tree risk assessment to the Washington Park Arboretum. Tree Solutions assessed three large native trees using sonic tomography, a device that measures sound waves to detect decay and other abnormalities in wood. Tree risk assessment is a vital component of maintaining the urban forest. Visual assessments typically provide more than enough information, but what cannot be seen yields valuable information to the Tree Risk Assessor. Healthy looking trees often have decay inside the trunk and limbs. The decay's extent and the tree's overall vitality determine management (pruning, cabling, removal). Traditional methods of assessing decay include sounding the tree with a mallet, using an increment borer, and drilling. The resistograph is a more sophisticated method which uses a fine drill bit and produces a printed record. In sonic tomography, sound waves sent through the tree are measured by sensors placed around the assessed part. These waves feed into a computer, which analyzes the input to produce a color image that accurately depicts both healthy and decayed wood. This detailed information greatly helps to manage the Arboretum's main attraction…the trees! Hazard Tree RemovalsA potentially hazardous Pinus nigra (Austrian Black Pine), located on Foster Island, is scheduled for removal on Tuesday, November 17. The pine is being removed due to its threat to the public's safety and nearby plant collections. This tree has declined rapidly and has likely succumbed to a blue stain fungus (Ophiostoma sp.) and red turpentine beetles (Dendroctonus valens). The debris and wood will be destroyed immediately to decrease the chance of spreading the fungus and beetle. Each tree requires evaluation to determine the best course of action. Hazards may be abated by pruning, cabling or removal. In appropriate locations, snags and fallen wood may be left for habitat enhancement. The service road near the pine tree will be clearly signed "Closed" for this removal and a detour will be set up to route pedestrians around the removal. For further information regarding this work, please contact David Zuckerman at (206) 543-8008 or by email at dzman@u.washington.edu
Thanks to the Washington State Department of Ecology, UW Botanic Gardens plans to begin a major attack on Lysimachia vulgaris (garden loosestrife), a state-listed noxious weed occurring along Union Bay shorelines including the Union Bay Natural Area and the Arboretum's Foster and Marsh Islands. King County requires control of this aggressive and invasive weed, which poses a serious threat to the native character of area wetlands. The DoE provided a 5-year grant for $75,000 to fund loosestrife control. In July and August, members of King County’s Noxious Weed Control Program and UW Botanic Gardens staff will map areas where the weed has taken hold. Afterwards, the weed will be treated with an aquatically approved herbicide by Northwest Aquatic Eco-Systems using airboats and other specialized equipment.
UPDATE: Arboretum Pine Mortality Washington State Department of Agriculture entomologists have been monitoring for the Arboretum's pine collection for insects that appear to be linked to increased pine mortality in the Pacific Northwest. The Arboretum first noticed pine decline in 2005 among its two and three-needle pines. For more information, click here for the Everett Herald's article, "Why are the white pines dying?" or click here for the New York Times' "Bark beetles kill millions of acres of trees in the West".
Dutch Elm Disease in the Arboretum
J.A. Witt Winter Garden: SE Bed Renovations
The UWBG horticultural crew will be making renovations to the southeast bed, which will include removing, relocating, or protecting other UW plant collections in the project area, followed by regrading of the bed and soil remediation. The 2009-2010 fall and winter planting of new winter-interest trees, shrubs, and ground covers will also take place. This project will reclaim over 5,000 sq. ft. of bed space that is now detrimentally shaded by elm trees. It will also renew UW Landscape Architecture Professor Iain Robertson's original 1987 Winter Garden design intent.
The Arboretum hortiucltural crew is continuing work in the Pinetum by the Arboretum's Newton Street entrance. Arborist Chris Watson is removing two poplars and one bigleaf maple in an undeveloped portion of the Pinetum that is also infested with ivy and other invasives. After clean-up, four large Taiwan cedars will be moved to the site. Woodland Garden Site prep continues for the planting of Frank Byle's maple collection.
For further information about stewardship of the Washington Park Arboretum, please contact WPA Horticulture Staff supervisor David Zuckerman at dzman@u.washington.edu
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Plant Stewardship
Sonic Tomography at the Arboretum
Taking Control of Garden Loosestrife
Three large dead English elms with Dutch Elm disease (DED) have been
removed from the Arboretum. Each tree was infested with the elm bark beetle, which is the vector for the
DED fungus. While the Arboretum's elm collection is small, it includes the historic Washington elms (Ulmus americana) and the amazing Camperdown elms, both of
which are susceptible to DED.
Horticultural staff are monitoring elms carefully for signs of infestation.
Pinetum
Collections Development