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NINAnor / ecosystemCondition

This repository is for documenting the design and calculation of indicators for ecosystem condition in Norway
https://ninanor.github.io/ecosystemCondition/
Creative Commons Attribution 4.0 International
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Reference levels - trophic level biomass ratios #113

Open anders-kolstad opened 10 months ago

anders-kolstad commented 10 months ago

At the end of the Reference values, thresholds for defining good ecological condition, minimum and/or maximum values sub-chapter it says "The choice of 40% is arbitary". Consider changing this to something a bit stronger worded, although it for sure is somewhat arbitrary. What about: "The choice of 40% is somewhat arbitary and based on the best guess, or intuitive understanding or the authors, and reflects the point where there are either too many or too few consumers to maintain important resilent ecosystem functions over time, such as avoiding excessive growth or depletion of one of the trophic levels with possible cascading effects through the ecosystems".

anders-kolstad commented 10 months ago

The lower reference value is not directly stated in the text I think, but it is introduced when truncating the %difference to 100%|-100%, i.e. a doubling or halfing of the expected biomass for the highest trophic level as compared to the expected biomass will translate to worst possible condition. This is perhaps a bit strict?

For example, an NPP of 5-10^6 kg C km-2 y-1 predicts a herbivore biomass of (5-10^6)^0.47*0.643 = 905 kg km-2

Perhaps this is something like 6 reindeer. Having 12 or 3 reindeer instead does not sound like such a big deal...

anders-kolstad commented 10 months ago

The %difference valiable is not normalised to the [0-1] scale, and probably this is why +-40% and -+100% were chosen as the reference values, but as I argue above, this excact truncation is perhaps not needed and we could have a wider tolerance for what is the worst possible condition, and then the 40% threshold value would ease up as well, cause now it is probably way to strict.