Colby trees project

Parks has received numerous requests from the residents along Colby Avenue to remove the Colby Avenue median trees because of root invasion that has cracked and elevated streets and sidewalks. Additionally, there have been reports of limbs falling, and some residents are reporting allergic reactions to the leaves and hairs that come from the trees. As a result, the Parks and Facilities Department hired two independent consultants to conduct a tree study to assess the health of the trees along Colby Avenue.   In addition, the departments’ Arborist also did an assessment.  This information was shared with the Park Board/Tree Committee who felt that Parks needed to come up with a long-term plan for the Colby median trees.

Eventually all the existing trees will need to be replaced, as they are near the end of their productive life span and are in steady decline.  However, this process will happen slowly and with lots of opportunities for community input.   Our Parks Arborist will continue to monitor the condition of all the trees along Colby Avenue annually.  Parks will contract with an independent consultant to evaluate the conditions of all trees along Colby Avenue every five years and will update the plan with any change in the condition of the trees in the report.   Trees that are considered dead, dying, or diseased would be removed. Once there is a significant ½ or full block of Colby with no trees, then soil remediation and replanting will occur.  Parks has gained public support to remove 1 declining tree, remediate soils and replant 3-4 new trees on the 1700 Block as a “demonstration area” to see how the public likes the trees selected.  We hope to start this project in the Spring of 2022.  If the demonstration area is well received, then progress on the steady replacement of the trees could move faster than what is outlined above.

The trees that were removed were identified by the Tree Study as trees that were dead, dying, or diseased.  As a result, Parks staff removed the trees that were considered high risk or in a critical condition.

In an effort to set the new trees up for success, Parks plans to remove the compacted nutrient depleted clay-based soil in the medians and replace it with soil that is well draining, healthy, and nutrient enriched that will allow the new tree root systems to grow deep down into the earth offering a strong, stable anchor, and better access to water, rather than crawling along the surface, searching for water and causing street and sidewalk damage, as they have in the past.  

Construction for the 1/2 block demonstration area will likely start in the Fall of 2022/Spring of 2023 based on the acquisition of trees that meet project specifications.

Eventually, all trees in the Colby strip will need to be replaced and replanted with a species that is more appropriate for the median.  While removing all the trees at once may be less expensive ultimately, Parks feels taking all the trees down at once would be a significant and abrupt change in aesthetic appearance.  Park’s funding is limited, and the removal and replanting process will likely happen over the next decade, as funding and project management time is available.   Parks would like to acknowledge that public support for this project is mixed, with as many people wanting the trees to be preserved as removed.  Parks has established parameters to assist with decision making process moving forward.   For example, for a ½ block remediation, the following parameters where presented:

• Once a block has 120 feet or more with no trees standing; or
• When 3 or fewer trees are remaining on a ½ block, and one of the trees has a risk rating above low, or a tree condition rating below fair, or the Park Arborist has determined one tree is in steady decline; and
• Parks has the money to perform the work; then
• Community outreach will begin around tree, stump and root removal, remediation of soils and replanting of new trees for that ½ block.

For the best outcomes, trees should be planted in soil that is permeable, so that roots can grow down, rather than expand out.  Additionally, trees should be spaced generously so they have room to grow out.  Finally, different species should be planted so that diseases common to some species are not spread through the entire block.  When Parks eventually replants, the soils will be remediated so roots can grow deep, the trees will be planted so there are no more than 7 per block, and at least 3 different tree species will be selected for variety.

Replanting will only start to happen as the public approves ½ and full blocks for soil remediation and replanting.   Part of the issues with the current trees along Colby Avenue involve over-crowding of trees, forcing them to compete for space and water. New trees will need to be spaced in a way overcrowding will not be a factor in the future.  Soil remediation will not be successful on a single tree basis because of the root system from other trees.  There are currently 68 trees standing on the Colby Avenue median. If we plant 7 trees per block, that will bring the total to 63 trees, or a net reduction of only 5 trees.  

Parks’ recommendation is for the following 3 tree species to be planted in place of the London Planes:

• Emerald Sunshine Elm (Ulmus Propinqua)
• Copper Beech (Fagus Sylvatica Atropupurea)
• Scarlet Oak (Quercus Coccinea)

Elm	Beech	Oak

Washington’s large native deciduous trees will not fit into the criteria that was developed when Parks is deciding on an appropriate tree for the Colby strip.  The criteria included:

• Tree must have a behaved root system
• Tree must still allow for good sight lines at intersections
• Tree must be a large shade tree
• Tree must be heat and drought tolerant
• Tree must be resistant to disease and pest infestation
• Leaves must not cause skin or lung irritation

Parks is recommending mulched beds between trees.  Mulch provides a more hospitable environment for trees to grow and is easily maintained, prevents damage from mowers to the tree trunks and roots.   Additionally, the breakdown of this organic debris will introduce further nutrients into the soil and reduce compaction.   If the public has interest, Parks is open to investigating other landscape options to fill in open areas between trees near the middle of the block.  However, these options must be low or no cost to maintain.

If the public had an interest in evergreens, Parks would suggest a short pyramidal shaped tree such as Austrian Pine (Pinus nigra) or columnar shaped trees such as Korean Fir, Weeping Alaska Cedar, or Columnar Spruce. These smaller conifers will be less likely to block sight lines and would be less likely to have people camping out under them.