St. Mary's Oak Tree
In February 2009, it was determined the Los Gatos Town arborist that our oak tree was "almost completely dead". St. Mary’s Oak Tree, which was once so majestic and beautiful, had succumbed to a fungal disease. Every effort was made to eliminate the fungus to no avail. The tree was removed the week of February 15, 2009. We are now in the process of looking into ideas as to how we renew the courtyard space. We will update parishioners when future plans become available. See photos of Oak Tree as it is taken down. If you have photos or know anything about the history of our oak please send via email to: History of Oak or drop off at Parish Office.
ESTIMATE OF AGE OF THE ST. MARY’S (SM)
OAK
Demolished in Feb, 2009 due to disease
BACKGROUND: The large Oak Tree in the courtyard of St. Mary’s Parish in Los Gatos was cut down in Feb 2009 (photo by Teri Tucci below – demolition in progress). This was due to the diseased and unrecoverable state of the tree. It was not possible to count the tree rings of the trunk directly. The age of the tree is important to the history of St. Mary’s which began as a Mission Church under the auspices of St. Clare Parish and the Jesuits at Santa Clara – the “Mission Days” – 1870 to 1912. It became a Parish in 1912. The Parish Centennial will be celebrated in just 3 years. An estimate of the age of the tree has been made below using three (3) methods . The conclusion is on p. 3.
METHOD 1 and 2 – BY GIRTH (CIRCUMFERENCE) There are estimating rules-of-thumb and tables available for Oak age as a function of girth.
Method 1, 25mm Rule. One rough rule-of-thumb is 1 year of age for every 25mm of girth (Note that there are 25.4mm in every inch). The literature suggests that this is one of the least accurate methods. (ref: http://uk.answers.yahoo.com/question/index?qid=20090114122649AAnDuaG). An estimate is provided below.
Method 2, Girth vs Age Table. A table from the Woodland Trust, “…for estimating the age of an oak tree,” provides for this estimate (below).
(ref http://www.woodland-trust.org.uk/ancient-tree-forum/atfresources/images/oakguide.pdf)
Both these methods require measuring the girth of the tree trunk – preferably at about chest height. However, no direct measurement of the SM tree is available.
An estimate has been made of the diameter of the trunk from photos taken during demolition (by Teri Tucci of St. Mary’s). That in turn allows an estimate of the girth.
Photo (left) shows the trunk cross-section with a worker right behind it. Based on that, the vertical diameter is estimated at 38 inches (The back, upper edge is above waist-high – at the chain saw. Assuming a worker of about 5’ 9” gives about 38”).
The trunk is not perfectly round, but it’s a fairly uniform ellipse, where the minor axis is 38”. So it’s necessary to come up with average diameter from the minor (vertical) and major (horizontal) axes.
The major axis can be scaled and calculated from minor axis in the photo. For the screen image used the minor axis was 57.9 mm, and the major axis was 81.8 mm. Using the photo estimate of the vertical axis (38”), the horizontal is calculated – by proportion – as 53.6 inches.
Averaging the 2 axes gives a nominal trunk diameter of (38+53.6)/2 = 45.8”. Thus an estimate of the nominal girth is (π x 45.8) = 143.9” – or 12’0”.
The 25mm Rule - Method 1 - says the SM Oak is about 146 yrs old. ((144”x25.4)/25 = 146.3)
The Woodland Trust Table (with interpolation) - Method 2 - says the SM Oak is about 175 yrs old.
METHOD 3 – BY TREE RING COUNTING
The most direct and accurate way of establishing age is by counting the rings in the cut cross-section of the trunk. Unfortunately, this could not be done on the SM Oak. Ref “How Old Is My Tree,” http://www.athensclarkecounty.com/documents/pdf/landscape_management/tcn_age.pdf
The age can be estimated before a tree is cut down by coring a sample of the trunk wood – counting those rings per inch, then applying that figure to the radius. The growing diameter can be calculated by measuring the girth – calculating the diameter and subtracting the bark thickness – 2x. (Ref http://uk.answers.yahoo.com/question/index?qid=20090114122649AAnDuaG )
In the case of the SM Oak, the trunk radius – including bark - is estimated from the photo measurements above (½ the diameter) at 22.9”.
A good alternative to a core sample was used to get an estimate of the “ring 
rate.” A cross-section of a large branch or limb (about 20” in growth diameter and saved from the remnants by Teri Tucci) was analyzed to get a representative ring rate. See photos of section. That rate was applied to the radius estimate obtained from the photos (above).
Note that another method is to apply a generic ring rate for that species of tree – which is subject to many variables. A sample from the same tree – the limb here - is much better.
See photo of rings (left).
The ring rate of the limb varied from 6 to 12 rings per inch. An average over a radius spanning the last 9 inches was 9.7 rings per inch. A rate of 9.0 is used here to be conservative. (The limb itself was about 90 years old – the most recent 90 years of the trunk’s age. Note that this and the main remaining limbs were relatively young, the older ones - low down - having been removed long ago)
The full trunk radius is 22.9” (45.8”/2). The thickness of the trunk bark is estimated at 1.5” (the thickness of the branch bark was 1”). So the ring growth radius is 21.4” (22.9 – 1.5).
Applying a growth rate of 9 rings/in – this yields an age of 193 years. (21.4 x 9 = 192.6)
The author had a White Oak in Los Gatos of similar size that was over 200 yrs old - with the rings counted directly, ca 1975.
SUMMARY OF AGE FROM 3 METHODS FOR SM OAK
CONCLUSION: When cut down in Feb 2009, the St. Mary’s Oak was probably over 170 yrs old – and might have been closer to 200 yrs old.
compiled by Robert Bresniker, PE (ret)
1 March, 2009
Note: Robert Bresniker, is a long-time member of St. Mary's Community. We appreciate his time and effort to compile the above information about our once beautiful oak tree.