Oak Tree Update- Results of Soil Investigation by City

Copied below is a letter we prepared to PWA Director Troyan, addressing the recent soil moisture investigation the City conducted around the oak.  As you will read, there are some issues. The City investigation report can be found on page three at: http://www2.oaklandnet.com/oakca/groups/cityadministrator/documents/report/oak032693.pdf 

Dear Public Works Director Troyan,

We have serious concerns with the findings of the “Status of Jack London Oak Tree” report included in the 12-16-11 City Administrators
Weekly Report.  These concerns include:

• December 8^th Investigation–Eight (8) inches is not a sufficient depth by which we can accurately assess the soil profile.  Due to the lack of understanding regarding where oak roots are, the one “fairly wet” soil sample taken close to 14^th street and within the cement retaining wall cannot be dismissed.
• December 14^th Investigation – Four(4) to six (6) inches is not a sufficient depth to assess soil moisture.  We would expect the soil to be dry at thisdepth in areas where water has not been applied.  Findings may be different deeper within the soil profile.  Also, findings for the four (4) soil samples reported to be taken beyond the concrete retaining wall were not included in the report.
• Root Depth – There is currently no information presented regarding the depth and location of oak roots and if they extend beyond the wall.  This informationis critical.
• Soil Texture – No information currently exists.
• Level of Soil Compaction – No information currently exists.
• Root Health– No information currently exists.

Upon visiting the plaza this afternoon, standing water surrounding the concrete retaining wall was observed in some of the lower areas.  Either the irrigation of the lawn has continued, or drainage is nonexistent in these areas.  Both represent “red flags” in regards to tree
health.

The actions we feel necessary to accurately access the root environment include:

• Soil Profile Investigation – A thorough soil profile investigation in numerous locations to a depth of 4-5 feet using a 3” bucket auger will determine depth and location of roots, soil moisture, soil texture, and soil compaction.  The investigation will occur outside the concrete planter, as this is the area that has endured the greatest level of impact (both compaction and water) and the area that would likely require mitigation.
• Laboratory Analysis – Soil and root tissue analysis can identify any nutritional deficiencies or excesses.  Leaf tissue analysis provides more accurate information when performed during summer months.
• Landscape Issues – Subsequent to investigation, we would like to have a serious discussion with City regarding alternative landscapes, at least in the area immediately surrounding the retaining wall.  Thank you again for your invitation to set up a future meeting.

Other issues include:

• Pruning –It may be prudent to remove the dead wood within the canopy.
• Current Plaza Design Plans –It would be most appreciated if we could obtain a general plan of the plaza, to assist with chronicling our soil investigation and with the possible planning of the area, if a project should move forward.  Information containing the depth of the cement retaining wall surrounding the tree would also be helpful.

We do understand the limitations of the City during these times and would be happy to offer our services to assess the tree.  We have contractor, arborist and City business licenses, as well as insurance, which may be necessary for qualification to work in the area.  We would gather the information noted in this letter and present the findings to the City.  We would do this work at no cost.

Looking forward to hearing from you after the holiday break,

Sincerely,

Molly Batchelder

“Flooding reduces the air-filled pore space in soils, reducing oxygen diffusion and, depending on duration in some cases, leading to
aeration deficit injury.  In addition to reducing soil aeration, flooding creates conditions favorable for infection by root pathogens, particularly when the soil temperature is relatively warm” (Costello, Laurence R., Bruce W. Hagen, and Katherine Jones.  Oaks in the Urban Landscape: Selection, Care, and Preservation.  The Regents of the University of California Agriculture and Natural Resources, 2011).

“Water in soil pores is a barrier to oxygen diffusion: oxygen diffuses through water 10,000 times slower than through air.  When the oxygen diffusion pathway (macropore space) is filled with water, the diffusion rate declines substantially.  This occurs in flooded soils, poorly drained
soils, and soils that are irrigated excessively.  It is particularly a problem in soils that have little macropore space to begin with (e.g., clays, compacted soils, and poorly structured soils).  In these soils, water occupies the space needed for gas diffusion, and oxygen cannot move to root surfaces rapidly enough to meet respiratory needs” (Costello, Hagen and Jones).