HomeMy WebLinkAbout03 14 2016 EAB Report
Phone 952.447.9800 / Fax 952.447.4245 / www.cityofpriorlake.com
4646 Dakota Street SE
Prior Lake, MN 55372
CITY COUNCIL WORK SESSION REPORT
MEETING DATE: MARCH 14, 2016
AGENDA #: 2
PREPARED BY: KATY GEHLER, PUBLIC WORKS/NATURAL RESOURCES DIRECTOR
PRESENTED BY: KATY GEHLER
AGENDA ITEM: RECEIVE A REPORT ON EMERALD ASH BORER (EAB)
DISCUSSION: The Minnesota Department of Agriculture (MDA) confirmed an emerald ash
borer (EAB) infestation in Prior Lake on Tuesday, August 25, 2015.
EAB is an insect that attacks and kills ash trees. It is spread through
transported firewood. The adults are small, iridescent green beetles that
live outside of trees during the summer months. The larvae are grub or
worm-like and live underneath the bark of ash trees. Emerald ash borer
larvae kill ash trees by tunneling under the bark and feeding on the part of
the tree that moves nutrients up and down the trunk.
EAB is native to eastern Asia but was discovered in Detroit, Michigan, and
Windsor, Ontario, in 2002. Indications are it may have been introduced to
this area as early 1990. EAB has been spread in ash firewood, nursery
stock and possibly other ash materials to a number of new areas. EAB
was found in St. Paul in 2009, the first Minnesota city.
All ash trees are susceptible to EAB and millions of ash trees have been
killed in infested areas already. Minnesota has the highest volume of ash
trees in the U.S. with almost a billion forestland and urban wood ash trees.
The potential economic and environmental impacts of losing these trees is
substantial. The cost of removing and replacing a single tree can range
from hundreds to thousands of dollars.
EAB-killed trees dry out quickly and become hazard trees in less time than
after a normal tree death. Hazard trees are trees that can be dangerous
because of the possibility of them falling over or large branches breaking
off, with a potential to cause personal injury to people.
At the onset of EAB the primary method for public agencies to address
EAB was removal and replacement. In fact a number of cities have been
proactively removing and replacing ash trees for several years to get out
ahead of EAB. However, areas that have been using treatment methods
for several years, such as in Michigan, are finding benefits to slowing the
spread of EAB and treatment costs are becoming more economical. The
most cost effective approach may be a combination of treatment and
removals considering the trees size, age, condition, location, and other
factors. In addition, indirect costs should be considered such as energy
2
savings, stormwater benefit and property value increases for saving larger
specimen trees.
In order to provide meaningful estimates of the impact to Prior Lake, an
inventory of ash trees is useful. Staff has been working on the inventory as
time has allowed. Staff focused efforts to document the City’s urban forest
in developed park areas first. This portion of the inventory identified 4,523
trees, 650 (14%) of which were ash. More recently the City has completed
representative sample areas that were used to estimate the total number of
public trees, including condition, within the City and has included streets
and trails. It is estimated that the City has 8,085 ash trees that will be
impacted by EAB. Attachment 1 shows the results of this analysis.
Using these estimates, an analysis was completed to show the potential
impacts of various scenarious to provide framework for the discussion. The
scenarios are described below and the attached charts show the potential
annual and cumulative costs. Based on the experience of other cities it is
estimated that the significant impacts to the urban canopy from EAB will
occur over the next 10-11 years. If no preventative action is taken, the
peak has the potential to hit within 6-7 years.
Base Case: Removal of all public ash trees as they succumb to EAB (more than 30%
canopy decline). Remove and chip in place woodland hazard trees. Replacement to start
in Year 9.
Ash Tree Preservation Plan A: Removal of public ash trees as they succumb to EAB.
Preemptive removal of some low-quality trees (Years 3-10). Remove and chip in place
woodland hazard trees. Treatment with emamectin benzoate of high -priority trees using
two protocols: Treat 1/3 of trees annually (3 cycles each Years 1 -9 years. Treat 20% of
trees annually through remaining years.
Ash Tree Preservation Plan B (Staged Removal Scenario): Same as ATP Plan A
except some medium and low-quality trees are treated over a 6-year period (2 treatments
each, Years 4-9) and then removed as they succumb to EAB. The purpose is to flatten
annual budgets during the peak of the infestation (Years 4-9), increase pest suppression
and herd immunity, and preserve tree benefits.
Ash Tree Preservation Plan B1 (Staged Removal Scenario variation): Same as ATP
Plan B except this scenario assumes the continued treatment of the low-quality trees that
were treated for staged removal. The purpose is to further reduce total budgets, increase
pest suppression and herd immunity, and preserve tree benefits.
ISSUES: Due to the changing landscape of treatment and abatement options for
EAB, the City will need to consider what approach to take for mitigating the
effects of EAB. Input will be sought on the following topics:
1. Does the City want to take a more proactive approach to ash tree
management on public property including rights-of-way by exploring
treatment options to extend the life of trees? Using the results of the
analysis, should the 2017 budgets include an additional amount for
treatments?
3
2. The analysis does not assume replacement upon removal to help
balance the costs over time. Is this the right approach?
3. The City currently has a diseased and hazard tree ordinance in place.
The ordinance provides the mechanism for the City to manage the
City’s urban forest by identifying and requiring abatement of trees found
to be harboring diseases or pests and any tree that is deemed to be
hazardous. Does the City want to manage EAB on private properties
similar to our management of Oak Wilt? If so we could expect to see a
significant increase in staff time allotted to identify EAB, follow-up with
the property owner, and complete enforcement if necessary.
3. Staff from Shakopee, Savage and Prior Lake have been discussing the
benefits of partnering on tree services and collaborating on
communications. A request for proposals has been drafted to seek bids
from treatment companies that ecourage a bulk rate that can be made
available to resdients. Staff will review the proposed program at the
work session and ask for concurance to move forward.
4. The cost of the impact of EAB could be considerable. The Minnesota
Shade Tree Advisory Committee (MnSTAC) has introduced a funding
request as part of the bonding bill. This request asks for $5.0 Million
over a two year period. MnSTAC is requesting support of this effort.
Should the City and/or SCALE support this effort?
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Analysis 031116, Populations