Washington Park Arboretum Oaks Rescued

February 7th, 2012 by UWBG Arborist, Chris Watson

Along with the constant rain and drizzle, winter in the Pacific Northwest often brings the occasional wind and snow events.  Damage to trees (and caused by trees!) is inevitable following these storms.  While wind events tend to cause the most spectacular tree failures, snow loads have been known to fell their fair share of limbs.  Damage to Arboretum trees has been lower than expected during the course of the most recent snow; however, our evergreen oak collection in Rhododendron Glen took a severe hit.

A 60-foot Canyon Live Oak (Quercus chrysolepis) uprooted, damaging another Canyon Live Oak and a Huckleberry Oak (Quercus vaccinifolia). The structure and foliage of these evergreen oaks provides a unique feel to this area of the Arboretum.  Preserving these trees was a high priority as losing them would be a dramatic loss.  In fact, the large Canyon Live Oak and the Huckleberry Oak are listed among the best specimens in the city in Arthur Lee Jacobson’s Trees of Seattle.

The tall Canyon Live Oak has an interesting history, as well.  Plant records indicate that this tree was grown from seed collected by Carl English Jr., for whom the botanic garden at the Ballard locks is named.

After a careful inspection, no root decay or extensive damage was observed on the large Canyon Live Oak.  Through the use of ropes, pulleys and a tractor, the tree was pulled upright, and supported by cables to a nearby tree.  After carefully installing a couple of braces, or steel rods, the smaller live oak will be spared a severe pruning.  As for the huckleberry oak, a minor crack in the main stem will be supported with a cable.

News stories following winter storms are often portray trees in a negative light.  However, through proper care and maintenance, most trees can withstand our seasonal storms.  Sometimes, when given a chance, the trees that receive the brunt end of Mother Nature’s fury can be given a new lease on life.  After all, trees are not only a vital component of our urban forest; they are one of our regions defining characteristics.


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Boyer Parking Lot Tree Protection

May 2nd, 2011 by UWBG Arborist, Chris Watson

One of the most widespread problems with trees in the urban environment is the failure to recognize the tree’s mature size.  If one doesn’t take into account the space required when the tree grows up, conflicts are sure to arise.  To make matters worse, the tree is often faulted for encroachment!

Several trees surrounding the Arboretum’s Boyer Parking Lot have grown up and encroached on the gravel parking spaces.  However, because we are advocates for the trees, we decided to make the parking lot yield.  A large scarlet oak (Quercus coccinea) and a grove of birch (Betula) were severely impacted by the concrete wheel stops and compacted soil over a large portion of their roots.  To remedy the problems, we moved the wheel stops to create a “root protection zone” around the trees.  Then, we used compressed air tools to break up the compacted gravel and soil.  We amended the soil with mycorrihizae and compost, then topdressed with a thick layer of mulch.  If all goes as planned, the additions will stimulate the soil biology, add nutrients and allow roots to grow in the previously uninhabitable environment.  Stay tuned for updates.

 

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Mason Bees in the Arboretum

April 13th, 2011 by UWBG Arborist, Chris Watson

With the goal of enhancing pollination efforts, several mason bee houses have been placed throughout the Arboretum.  What are mason bees?  Well, according to the provider of the pollinators, Dave Richards of JohnnyAppleBeez, LLC:

“The charming Mason Bee is a gentle, shiny blue-black metallic bee, and slightly smaller than a honey bee. They are a superior pollinator, but do not produce honey. Only 350 females are needed to pollinate an acre of apple trees rather than 25,000 honey bees.  After emerging in the spring from cocoons, these solitary bees first mate, then the female begins to forage pollen and nectar from flowers for next year’s offspring.

The Mason Bee gets its common name from their nesting habit of using mud to create protective partitions for their young when reproducing. When the female has provided a sufficient supply of food for the larva, she lays an egg and then seals the cell with a thin mud plug. She then provisions another cell, and continues in this fashion until the nesting hole is nearly full. Finally, the bee plasters a thick mud plug at the entrance to protect the offspring from predators and the weather.

They are not aggressive and they may be observed at very close range without fear of being stung, unless they are handled roughly or if trapped under clothing. In nature, the Mason Bee nests within hollow stems, woodpecker drillings, and insect holes found in trees or wood. Sometimes, there may be dense collections of individual nest holes, but these bees neither connect or share nests, nor help provision or protect each other’s young. Their short foraging range is about 100 yards from the nest. Depending on the weather and available food, activity continues for around four to six weeks and then the adults die.”

The bee houses will remain secured in trees until late June, when the new cocoons will be collected for next year.  Eight boxes are located along Arboretum Drive, Azalea Way, and Pacific Connections.  Can YOU find all of them?

 

 

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Losses to UWBG Pine Collection

April 11th, 2011 by UWBG Arborist, Chris Watson

A turkish pine (Pinus brutia) and a Chinese white pine (Pinus armandii) were recently removed from the Canal Reserve area near the Museum of History and Industry.  Both trees declined suddenly over the past year and died over the winter.  Blue staining was evident in the wood of both trees.  We’re not sure exactly how these trees are infected with the fungus, but one theory is that a bark boring insect (red turpentine beetle) carries the pathogen into the tree.  These beetles appear to be secondary pests, meaning they attack stressed trees.  The beetles lay eggs in galleries under the bark and the larvae overwinter in these galleries.  The new generation of beetles emerges in warm weather the following spring.

Because these insect pests are secondary, management of our pine collection is focused on alleviating stress through deep root aeration, compost and mulch applications.  Dead or severely declining trees are removed and the wood and brush are destroyed immediately to stop the spread of beetle.  Persistent monitoring helps staff prioritize which trees need the most help.  Over time, we should be able to minimize losses to the collection and keep our remaining pines healthy.

 

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Spring Pruning at the Arboretum

March 30th, 2011 by UWBG Arborist, Chris Watson

Recent Arboretum visitors may have noticed some unusual pruning, specifically in our Holly and Camellia collections.  The camellia specimens, located near the Lookout parking lot, will be re-propagated and planted in a different location to make space for the Pacific Connections New Zealand focal forest.  Large heading cuts were made to induce new epicormic growth, or watersprouts, which are ideal for propagation.  Cuttings for propagation will be taken later this summer.

The hollies can be found along the south side of Boyer Ave. near Lake Washington Blvd.  These hollies have been struggling since they were transplanted several years ago.  While not quite as radical as the camellia pruning, some might be surprised to see this style of pruning in the Arboretum, myself included!  However, in his book Hollies: The Genus Ilex, Fred Galle refers to a style of pruning called “hatracking or coatracking…best done in early spring, so new growth begins to cover the bare stems the first season…In two years the plants will show no signs of being severely pruned.”  We hope that this harsh pruning will induce a flush of new growth that rejuvenates these declining specimens.  Stay tuned for updates.

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Sonic Tomography at the Arboretum

March 18th, 2011 by UWBG Arborist, Chris Watson

The University of Washington 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 a large western hemlock (Tsuga heterophylla) using sonic tomography, a device which measures sound waves to detect decay and other abnormalities in wood.

Assessing the risk associated with trees is a vital component to maintaining the urban forest.  Visually assessing a tree can often give more than enough information.  However, what cannot be seen can yield valuable information to the risk assessor or manager.

It is normal for trees that appear healthy to have decay inside the trunk and limbs.  It is the extent of this decay, along with the overall vitality of the tree that determines management (pruning, cabling, removal).  Traditional methods of assessing internal decay include sounding the tree with a mallet, increment borer, and drilling.  A more sophisticated method is the resistograph, which determines the decay extent using a very fine drill bit and produces a printed record.

Among the very latest technology is the minimally invasive procedure (i.e. no drilling!), sonic tomography.  Sound waves sent through the tree are measured by sensors placed around the assessed part, which feed into a computer.   The computer analyzes the input producing a color image which accurately shows healthy wood and decayed wood.  This detailed information greatly helps in determining management of the Arboretum main attraction…the trees!

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