Forecasting : interaction of mortality rates

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anne-sophie.lessard
Posts: 5
Joined: Tue Aug 23, 2022 1:18 pm

Forecasting : interaction of mortality rates

Post by anne-sophie.lessard » Tue Sep 13, 2022 8:59 am

Hi! I have a question about the “Forecasting” module of iTree Eco. It is possible to specify annual mortality rates using different tools: “Annual Mortality Rates”, “Pest Outbreaks” and “Weather Events”. I wonder how these different rates interact. For example, if I specify custom mortality rates for a certain genus (eg. annual mortality rate of 6%), and pest outbreaks affecting this same genus are also added to the model (eg. annual mortality rate of 4%), what will be the resulting mortality rate for this genus for the years when the outbreaks occur? In this example, will it be 10%? Thank you!
Jason.Henning
i-Tree Team
Posts: 340
Joined: Fri Dec 21, 2012 7:45 am

Re: Forecasting : interaction of mortality rates

Post by Jason.Henning » Fri Sep 16, 2022 12:05 pm

I had our developer take a peak under the hoods to verify how multiple mortality rates are applied. Essentially they are additive as you suggested. All the mortality rates are applied to the number of trees that start a given time period.
Total killed trees = (killedByPests + killedByMort + killedByWeather)
The exception is how the general mortality rates, those not associate with weather or pests are applied. See the pseudo code below for additional details on the generally mortality.

killedByMort: the mortality is determined as:
The mortality rate is a little more complicated. Below is the logic.

Mortality rate is dieback related.
Dieback: 1. If the project is collecting dieback, use the dieback entered for existing trees. New planted trees will take the smallest dieback (healthiest condition) that is defined in configuration.
2. if the project is not collecting dieback, all trees will use the default dieback 13%

Mortality:
1. If the dieback is >=75%, take the base mortality rate. Other specified mortalities (strata, condition, genus) do not take effect
2. If the dieback is >=50% and <75%, take the base mortality rate. Other specified mortalities (strata, condition, genus) do not take effect
3. When dieback is < 50%:
a. Take the mortality rate specified according to following precedence: strata, condition, genus genus, condition, strata, if any specified
b. If no mortality rate specified by strata, condition and genus, use the base mortality rate for dieback category of <50%.
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anne-sophie.lessard
Posts: 5
Joined: Tue Aug 23, 2022 1:18 pm

Re: Forecasting : interaction of mortality rates

Post by anne-sophie.lessard » Tue Sep 20, 2022 8:40 am

Hi Jason!
Thank you for these clarifications!
Best,
Anne-Sophie
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