Ash Reduction Model Tutorial
Tara L. Eberhart, Andrew J. Storer, Linda M. Nagel
© Michigan Technological University
Houghton MI, 49931
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
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.
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
Input Requirements Version 2.0
You will need the following information to run the Ash Reduction Model found at www.ashmodel.org:
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.
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
Interpreting Outputs of the Model
% Surface Area Column - The column to the right of the green Trees per
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.
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
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.
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.
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.
Funding for this research was
provided by the USDA Forest Service Northeastern Area and was conducted at the
Links for more information on Emerald Ash Borer
Tara L. Eberhart
Andrew J. Storer
Linda M. Nagel
About the Authors
Tara Eberhart is a Graduate Research Assistant., Andrew
Storer is Associate Professor of Forest Insect Ecology, Linda Nagel is Assistant Professor of Silviculture,
and Mike Hyslop is a GIS analyst in
Fax: (906) 497 – 2915
Cover photo by Jessica Metzger
Emerald ash borer photo by Andrew Storer