Forecast module mortality rate

[akunsch]

Hello,

Do you have the methodology / source for the default assumption of a 3% annual mortality rate for healthy trees? I am using the module for some simulations and would love to support the mortality rates with appropriate literature. See the i-Tree Eco description below:

"Base annual mortality rates (%) – The values presented here show the default annual mortality rates for healthy trees with 0-49% dieback (3.0% annual mortality), sick trees with 50-74% dieback (13.1% annual mortality), and dying trees with 75-99% dieback (50.0% annual mortality). You may change the base mortality rates for each of these condition classes. The rate that you provide indicates the percent of trees in that condition class that will die each year. For healthy trees, this mortality rate is an average starting rate that is adjusted up or down depending on the tree DBH class."

Thank you,
Antoine

[Jason.Henning]

It is not a well documented number. It is more of a rough average of what is generally commonly reported in the arboriculture literature. There aren’t a lot of good mortality numbers anywhere in urban forestry and those studies that do exist do not cover all conditions like yard plantings, natural areas, planting strips, etc. We encourage users to edit that number to reflect local knowledge and the exact population of trees they are working with. Alternatively, many people run high, low, and moderate mortality scenarios to capture that variability and the importance of maintaining trees.
In the future we are looking to include more relevant mortality rates that may use the user's collected plot data or long term monitoring data such the US Forest Service Urban Forest Inventory and Analysis program.
Thanks,
Jason

[wrl]

Hi,

In regards to mortality rates for trees and running a forecast:
The littérature reports quite high mortality rates (26-40% depending on study) during the establishment period of trees. I was wondering if this is incorporated in the model, or if not, if it makes sense to add an extreme event (pest/weather) for trees in their establishment period when running a forecast?

Kind regards,
William

[Jason.Henning]

Hi William,
Forecast is very flexible so you can design your mortality rates to reflect whatever levels you would like. You could modify the base mortality rate to capture your desired establishment phase mortality. If you are looking to model past establishment phase, you could create annual mortality events to simulate your expected mortality for your desired the number of years representing what you determine to be the establishment phase. Weather events are generally easier to use for this purpose because they impact all species where pest events may only impact host species.
Because it is impossible to know the scenarios that users are trying to model with Forecast we always recommend that users adjust mortality rates and add mortality events to reflect real world circumstances. It is very unlikely that the default settings will be the most accurate for any given scenario.
Thanks,
Jason