HomeMy WebLinkAbout8/25/2020 Item 03, Hill
Wilbanks, Megan
From:
2020 2:12 PM
To:Wilbanks, Megan
Subject:RE: Additional information re: tree committee - 1288 Morro
From: Arbor First <
Sent: Monday, August 24, 2020 1:54 PM
To: Combs, Ron <rcombs@slocity.org>
Subject: Additional information re: tree committee - 1288 Morro
Hi Ron:
Attached please find some additional information that I would like to submit to the tree committee for their
review. Thank you for forwarding it!!
Take care,
Bob Hill
Arbor First
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Cell – 805.441.3715 / Office-Fax – 805.772.5400
170 Terra Street, Morro Bay, CA 93442
www.arborfirst.com / arborfirst@sbcglobal.net
August 24, 2020
City of San Luis Obispo
Tree Committee Via E-mail
` rcombs@slocity.org
Re: ITALIAN STONE PINE TREE (Pirus pinea) / 1288 MORRO STREET
Dear Committee Members:
Please be advised that we have addressed the above referenced Italian Stone Pine tree
numerous times over the last 4 years. Incidents that have necessitated our attention
include: dropping large (approximately 18 – 20” in diameter) leaders into the parking lot
covering multiple spaces, heaving of asphalt in multiple places and heaving of sidewalks
in multiple places along the walk way. The building adjacent to the subject tree includes
a medical clinic serving veterans, many of whom have difficulty navigating the uneven
and broken hardscape.
This particular species of tree is inherently unstable. As evidence, attached please find a
study completed by L.R. Costello, J. Tso & K.S. Jones and published in the WESTERN
ARBORIST.
It is our contention that this is a wrong tree in the wrong place. To minimize the potential
of harm to people and property, the tree should be removed.
If you need further information regarding this issue, please do not hesitate to contact this
office.
Sincerely,
Robert Hill
WESTERI Arborist
Straeftod ldhm poop Me: Bf @Rkm of o at)
pine QNrswg fgrsoaD
L. R. Costello, J. Tso, and K. S. Jones
ACH YEAR, THE STRUCTURAL FAILURE OF
trees in urban and forested recreation areas results
in personal injuries and property damage. A key
objective of a tree management program is to reduce the
potential for failure to the extent possible. One important
element of failure reduction strategies is to prevent or miti-
gate conditions that may lead to failure, such as pruning
branches weakened by wood decay, cabling or bracing,
and avoiding root damage.
All tree species do not fail in similar ways, however.
Some are prone to fail as a result of weak architecture, such
as codominant stems. Others have a greater propensity to
fail because they develop large end -weights on branches
--- exceeding the load tolerance of the wood. Knowing the
particular failure patterns of species can help tree managers
identify key defects that may lead to failure.
By collecting detailed information following the failure
of a tree, data can be compiled and then used to develop
structural failure profiles for species. Such a profile has
Figure 1. Italian stone pine is a relatively common land-
scape tree in California. Typically, it has a rounded crown
and multi -stem structure. Photo: K. Jones.
By collecting detailedinformation following tie failure
of a tree, data can be com-piledandthen usedto develop
structuraCfaiCure-profiles for species.
been developed here for Italian stone pine (Pinus pinea) us-
ing data from the California Tree Failure Database (CTFD).
Arborists and foresters can use this information to develop
structural management strategies for Italian stone pine.
The development of this profile was commissioned by the
Britton Fund of the Western Chapter of the International
Society of Arboriculture.
Italian stone pine distribution
Italian stone pine is native to southern Europe and Tur-
key, but has become naturalized in many regions with a
Mediterranean climate. It is a relatively common landscape
tree in California, being found in both public and private
landscapes (Fig. 1).
General statistics
There are a total of 170 reports in the CTFD for Italian
stone pine, the majority of which are for root failures (41 %).
Trunk failures comprise 30% of reports, and branch failures
Jall 2015 44
make up the remaining 29%.
Reports came from 22 counties, but the majority (75
reports) are from Contra Costa, San Francisco, and Santa
Clara Counties. Italian stone pine failures are slightly more
common in winter than summer, with 52% of failures re-
ported from December to February. General statistics for
all failure types can be found in Table 1.
. ° ' o - ° lfCJxLLfL
Variable
Mean
Age
43 years
Height
47 feet
DBH
32 inches
Crown spread
44 feet
Figure 2. Many Italian stone pine branch failures occur
at the attachment, rather than along the branch. Heavy
lateral limbs (end weights), dense crown, and multi -stem
structure were reported to be associated with branch fail-
ures. Photo: C. Rippey
Most failed trees were found in a group (57%), in high
use areas (59%), and in residential areas (36%). The most
common defect for all failures was dense crown, observed
in 21 % of reports, followed by multiple/ codominant trunks
(20%) and leaning trunks (15%).
A. BRANCH FAILURE
Branch failure was reported in 50 cases, or 29% of all
reports.
Branch failure location
The majority of branches failed at the attachment (60%)
(Fig. 2). Failures along the branch occurred largely within
3' of the trunk (40%), with diameter of the break highest in
the 5-12 inch range (60%). The majority of trees with branch
failures were between 26 and 50 years old (59%).
The main structural defects observed in trees with
failed branches are heavy lateral limbs (observed in 43%
of cases), dense crowns (21%), and multi -stem structure
(15%) (Table 2).
Decay and branch failures
Decay was reported in only one branch failure case, less
than 25% of the cross -sectional area was decayed, and a
sporophore was not found. All other reports, comprising
98% of total cases, reported no decay.
L° UaLla
Defect
Frequency
Heavy lateral limbs
43%
Dense crown
21%
Multi -stem
15%
WESTER rlArborist
Wind and branch failures
Although more failures occurred in low wind conditions
where wind speed did not exceed 5 miles an hour (35%),
failures were distributed quite evenly across low, moder-
ate, and high wind speeds (Table 3).
7Windspeed "M7Fcrequen�c'y
of
curanc
Low wind (<5 mph)
35%
Moderate wind (5-25 mph)
32.5%
High wind (>25 mph)
32.5%
Precipitation and branch failures
The majority of branch failures occur during dry conditions
(62%), while the remainder occurred during a precipita-
tion event.
Pruning and branch failures
Pruning had not been done in 63 % of branch failure cases,
while 28 % of cases indicated that the tree had been thinned.
The remainder of reports did not indicate whether pruning
had been done or not.
B. TRUNK FAILURE
Trunk failures accounted for 30 % of Italian stone pine fail-
ures. Most occurred above ground level (55%), while the
remainder (45 %) occurred at ground level. Trunk diameter
at the point of failure ranged from 7 to 54 inches, but the
majority (44 %) were between 13 and 24 inches in diameter.
The primary defect associated with trunk failure is multiple
trunks/codominant stems, observed in 44% of cases, fol-
lowed by dense crown (28%) (Table 4 and Fig. 3).
Decay and trunk failure
Decay was not present in 76% of trunk failure cases (Fig. 4).
In 90% of cases where decay was found, less than 50% of the
cross -sectional area was decayed. Sporophores were observed
at the point of failure in only two trees, or 4% of cases.
�. o-�4 D - - o 0 - e .
L9ll°JJLLr1 -
• - e
Defect
Frequency
Multiple trunks/codominant stems
44%
Dense crowns
28%
Leaning trunk
8%
45 Jall 2015
WESTERI Arborist
Figure 3. (Above) Codominant stems and multiple trunks
were the most commonly reported defect causing trunk
failure in Italian stone pine. Here, a large comdominant
stem failed at the point of attachment. Embedded bark is
not commonly found in such failures in P. pinea.
Figure 4. (Below) Decay was not present in 78% of trunk
failures, but dense crown was reported to be a key factor.
Here, an Italian stone pine with a dense crown failed at a
point high on the trunk. No decay was evident.
Precipitation and trunk failures
Slightly more than half (54%) of trunk failures occurred
during wet conditions, while the remainder of cases oc-
curred during dry conditions.
Wind and trunk failures
Trunk failures most commonly occurred during low wind
conditions between 5-25 mph (40%), but distribution was
fairly even across low, moderate, and high wind condi-
tions (Table 5).
C. ROOT FAILURE
Root failure is the most common failure type, with 69 re-
ports, or 41 % of the total (Fig. 5). Trees experiencing root
fall 2015 46
Wind speed
Frequency of
occurance
Low wind (<5 mph)
40%
Moderate wind (5-25 mph)
28%
High wind (>25 mph)
32%
Figure 5. (Above) The most common type of failure in Ital-
ian stone pine is uprooting. Although dense crown is fre-
quently associated with root failures, decay is not. Photo:
C. Llata.
Figure 6. (Below) Girdling roots are reported to contribute
to a number of failures in Italian stone pine. Here, a gir-
dling root occurring at ground line was linked to the failure
of this Italian stone pine. Photo: C. Rippey.
Table 6. Defects reported
root failures.
Defect
associated with
Frequency
Leaning trunk
29%
Kinked/girdling root
18%
Dense crown
15%
-OuDhT.WDA o--aag Uwe Mau,
Wind Speed
Frequency of
occurrence
Low wind (<5 mph)
30%
Moderate wind (5-25 mph)
23%
High wind (>25 mph)
47%
failure ranged from 7 to 100 years old, with the majority
(76%) aged 11-50.
W E ST E Rk,�Iborist
bodies were observed near the failure location in only 16%
of trees with decay.
Wind and root failures
The majority (47%) of root failures occurred during high
wind conditions, while 30% and 23% of failures occurred un-
der low and moderate wind speeds, respectively (Table 7).
Precipitation and root failures
Precipitation was reported in 67% of root failure cases.
Saturated soil conditions were reported in 32% of cases.
L. R. Costello
Oracle Oak, LLC
Defects and root failures
The most common defects were lean (29%), kinked or J. Tso
girdling roots (18%), and dense crown (16%) (Table 6 and MS, UC Davis
Fig. 6).
K. S. Jones
Decay and root failures CTFRP Database Manager
Decay was not present in 67% of root failure cases. Fruiting
Summary of Key Findings
> Root failure is the most common type of failure
in Italian stone pine (41%).
> The majority of branch failures (60%) occur at
the point of attachment.
Heavy end weight, dense crown, and multi -
stem structure were key factors contributing to
branch failures.
> Multiple trunks/codominant stems, dense
crown, and lean were key factors contributing
to trunk failures.
> Lean, girdling/kinked roots, and dense crown
were key factors contributing to root failures
(Fig 7.).
> Decay was not present in the majority of
branch, trunk, and root failures.
Where decay was present, sporophores (fruiting
bodies) were rarely found.
> Embedded bark was reported in only 4% of trunk
and branch failures.
> Root failures were associated with precipitation
and saturated soils, while trunk and branch fail-
ures occurred almost as frequently during either
dry or wet conditions.
Wind played a role in the majority of root fail-
ures (47%), while branch and trunk failures were
distributed fairly uniformly during low, moder-
ate, and high wind conditions.
Fig. 7. Lean has been reported as a key factor contrib-
uting to root failure of Italian stone pine. Here, large
props have been installed to reduce the failure poten-
tial of this leaning specimen. Photo: T. Kipping.
47 Jall 2015