Stock and Flow Model

[ahunt]

I am becoming familiar with the ST-Sim stock and flow add-on, and have gone through the documentation and video tutorial. We are wondering if the stock and flow package can be used to track the development of snags and downed wood through time. It seems straight forward to use it for flows from snags and to downed wood since the latter is easily estimated from snag fall rates. However, while it’s easy to determine flows into the snag stock based on proportions of fire and insect/disease transitions, the amount of snags is dependent on the proportion of the state class disturbed, not on the amount of the snag stock itself. So, would I have to first create a state attribute for snags, which would be dependent on a percentage of a state class disturbed, then use the stock and flow function to track snag fall into the downed wood stock, or is there a way to model the stocks and flows of both snag creation and snag flows into downed wood in one combined S&F model?

[leonardo-frid]

Hi Ayn,

You are correct that the ST-Sim stock flow add-on can be used to track snags and downed wood. Stock flow models typically maintain a mass balance across all stocks so it is best to include stocks for live biomass, atmosphere and soil also. A really good example that includes snags and downed wood is included as a template from the ST-Sim CBM-CFS3 add-on package which includes flow pathways and rates from live to snag and snag to downed wood stocks. Typically the rates are both included for automatic flows (i.e., biomass turnover from natural mortality) and disturbance driven flows (i.e., wildfire and timber harvest).

Here is the landing page for the ST-Sim CBM-CFS3 add-on which includes a “Getting Started” guide: https://apexrms.github.io/stsimcbmcfs3/
A paper worth reading is Sleeter et al. 2022: https://doi.org/10.1186/s13021-022-00201-1

Hope this helps!

Regards,
Leonardo

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