Ash
Reduction Model Tutorial
Version 2.0
Tara L. Eberhart, Andrew J. Storer, Linda M. Nagel
© Michigan
Technological University
1400 Townsend Dr.
Houghton
MI, 49931
Updated April 2, 2007
Abstract
The Ash Reduction Model is a website intended to help
forest resource managers reduce the amount of ash resource available to emerald
ash borer (Agrilus planipennis) and
thereby reduce the insect’s potential population density. Version 2.0 of the model was formulated with phloem
thickness data collected from over 500 ash trees in order to find the average phloem
basal area of any given ash (Fraxinus spp.,
Oleaceae) tree within a desired size class.
The phloem tissue is the critical resource utilized by
emerald ash borer. Ash Reduction Model 2.0
takes into consideration ash tree phloem basal area, which is a good indicator
of the relative amount of phloem available to emerald ash borer based on the
size of the tree and its growing conditions.
Using Trees per Acre as the input data, managers can view the model
outputs which include the diameter limit for removal of ash to achieve the
specific reduction target percentage.
Use
of the model will limit the population potential of emerald ash borer, thereby
reducing its impacts and potential spread.
Using diameter limit cutting on ash trees in a stand allows for
retention of some trees in order to help preserve ash genetics and maintain it
as a viable part of our forest. The
model shows outputs for retaining small trees as well as large diameter ash
trees, depending on the manager’s decision.
This manual gives an example using real stand information that explains
where to find the model, how to input data, and read the results. Future models may incorporate ash species,
growing conditions, geographic location, and remaining stand basal area.
Introduction
Welcome to the Ash Reduction
Model – a website created to help with management decisions in removal of ash
trees to reduce the population densities of emerald ash borer. This tutorial provides background on the model,
instructions for inputting data and how to use the information given by the
model.
The model is designed to
work with diameter limit harvesting silvicultural proscriptions. This short tutorial will be useful to first
time users of the model for reading the outputs and to see what data they need
to enter into the model. As the model
versions progress with additional factors taken into consideration, the
tutorials will be updated.
Why use this type of model?
At high population
densities, this insect is capable of attacking and killing green, black and
white ash. Long-term prospects for management include biological control to
reduce population densities of the insect, and resistance or tolerance of ash
trees to reduced population densities of the pest. In the short term, reduction
of pest populations in local areas is achievable by removal of its breeding
substrate.
Removal of ash from stands
such as those in close proximity to outlier populations will reduce the
population density of this insect, thereby reducing EAB impacts and potential
spread. The amount of phloem available
to the insect in a forest stand containing ash can be measured from tree cores
and samples removed from down trees.
Models of the amount of ash tree removal necessary to reduce EAB
breeding substrate by a target percentage have been developed.
How does the model work?
The Ash Reduction Model
Version 2.0 is based on ash species specific phloem. The data used to calibrate the model comes
from over 500 ash trees in a variety of rural sites throughout Michigan and northern Wisconsin that were measured in 2005. The models find the percent phloem basal area
by diameter of ash in a stand were developed from basal area of the tree minus
the phloem tissue. This is representative
of the phloem in a tree that is available to emerald ash borer as phloem
thickness is dependent on size of the tree and growing conditions.
Getting
Started
Input Requirements Version 2.0
You will need the following
information to run the Ash Reduction Model found at www.ashmodel.org:
- Number of Trees per Acre of ash (Fraxinus)
species
- This is a measurement of tree density and can
be determined from stock and stand tables. Use only ash species in the stand, not total Trees/Acre. Contact your local forester for more
information. Diameter class can be
2”, 1”, or 2cm, 1cm classes.
Note: This model only works with the ash component
of a stand regardless of total stand size, other tree species presence, or how
much total ash there is present.
Using the Model
The model can be found at www.ashmodel.org.
Figure 1 –
Ash Reduction Model homepage
At the bottom of the page is
a link to this manual and below that a link to the model input page (Model
Version 2.0). Click on this to open the
input page.
The Input
Page
Once the input page is open,
the user can scroll down and see information about the model, two tables of
target percentages, an empty chart, and to the left a column of diameter
classes and empty green cells for the user’s Trees per Acre data.
Figure 2 –
Top of Model input page
Notice the 3 buttons at the top and bottom of
the page:
Update – after data has been entered in the green columns,
Update will refresh the page to reflect the correct % Surface Area and Diameter
Limit to cut
Clear – will erase data in the green columns and
start the page blank
Print – will print the outputs
Multiple Diameter Class Models
The user will have noticed that
there are 4 model versions available, which may be used depending on the type
of data information the user has. 1”,
2”, 1 cm, and 2 cm models are available to allow for different inventory data.
Entering Data
The Ash Reduction Model will
automatically start with 0.0 in each of the green Number Trees/Acre cells. This is where the user will enter their
data. After all of the numbers have been
entered the user may click update to refresh the page or hit the Tab key
on their keyboard after each entry to update the page automatically
Figure – 3 Empty input page
The example in Figure 4
shows real stand data that has been entered, with the % Surface Area that the
Trees per Acre in that stand represent. The Cumulative Percent Surface Area in the
chart shows what Diameter limit corresponds with the cumulative percent. The Target Percentage tables at the top show
specific diameter limits for target percentages of surface area that may be
chosen to remove.
Interpreting Outputs of the Model
% Surface Area Column - The column to the right of the green Trees per Acre column shows what percent of the total surface area in the stand that
that particular diameter size class represents.
This information is used to compile the cumulative surface area that is
graphed in the charts.
Relationship Cumulative Surface Area
and DBH charts & Target % tables – Notice the output charts cumulative surface area to retain small
trees, the most common type of diameter limit harvesting, which is removing all
trees above a specified diameter at breast height.
Figure 4 –Output chart
The
first chart corresponds with most common type of diameter limit harvesting of
retaining small trees, which is removing all trees above a specified diameter
at breast height. This chart matches up
with the first table on the top left Retaining Small Trees that shows
what the specific diameter limit is when targeting a certain percent removal of
ash surface area as shown in Figure 4.
In this example, to remove 95 % of the surface area available to EAB, all
ash trees greater than 4.4 inches should be removed.
Another
way diameter limit harvesting is done is by removing trees to retain large
trees. An output of this type of
modeling would be the same graph but with the cumulative surface area
ascending. The user will see that the diameter limits shown in the bottom table
on the right to retain large trees are much larger than in the table to retain
small trees.
With
this type of harvesting, the forest manager can still remove a target amount of
surface area or phloem available to emerald ash borer but retain seedlings
(trees to small to be cut at all) and the larger diameter trees. The diameter limit given for this type of
harvesting indicates the size at which trees are left rather than cut, so all
trees less than the specific diameter are removed. Using this example, to retain large trees and
still remove 95 % of the ash surface area, all trees less than 19.6 inches
should be removed.
Summary
These
models are available to forest resource managers so that they may be used to
determine a diameter limit to retain ash trees as a component of our
forests. This management strategy will
not eliminate emerald ash borer from our forests but it may reduce their
population impacts on our remaining trees after the diameter limit
harvest. The model can be used with 1 or
2 inch diameter classes as well as metric data and will find diameter limits to
retain large or small ash trees.
Common Questions about the Ash Reduction Model
- Do all
diameter classes need to have trees per acre?
No,
a diameter class with no trees in it may be left blank and the model will still
work. A straight line may appear in the
chart output; however this has no negative effect on the calculations and a
target % may still be found.
- Where
can I get trees per acre information from if I don’t have a stand table?
Contact
your local forester, a forestry extension official from a university, or a
consulting forester. Trees per Acre
is a measure of stand density that is calculated from stand basal area.
- Will my
remaining ash trees be protected from emerald ash borer?
No,
that is not the purpose of the model.
Using target ash reduction as a management tool will reduce the
population potential of eab by taking away a targeted % of their critical
resource, ash phloem. This will reduce
the potential for eab population buildup in an area, therefore minimizing its
impact and possibly slowing its spread.
