Closed JunyanDing closed 1 year ago
rosiealice
commented
2 years ago Hmm. I have a recollection that we changed it to be a site level property a while back , to avoid a different set of artifacts. Do you remember @ckoven @rgknox ? It might have been pre-github?
ckoven
commented
2 years ago @JunyanDing yes we changed this a while ago, see here: https://github.com/NGEET/fates/pull/279 Sorry it didn't get updated in the tech note, we should make a note to do that. In general, and in the interest of keeping things as simple as possible, I tend to suggest that unless specifically interested in the crown plasticity question one should set the min and max values of the crown allometry coefficient to be the same value, effectively turning this logic off.
ckoven
commented
2 years ago noting that we already have a reminder to fix this in the tech note (now three years old, so a slightly depressing indicator of the lag in updating the tech note). https://github.com/NGEET/fates-docs/issues/12
JunyanDing
commented
2 years ago I see. Thanks for pointing me to those earlier issues @ckoven! Unfortunately, my oak is highly plastic :-(
The current canopy spread term is a site level property, calculated based on the average total crown area per ha across all the patches and cohorts. https://github.com/NGEET/fates/blob/master/main/EDTypesMod.F90#L814 https://github.com/NGEET/fates/blob/master/biogeochem/EDCanopyStructureMod.F90#L1220 This is not the same as described in the tech notes (patch property indexed by canopy layer, table 1.3), and could cause two artifacts: 1) With fire, it will underestimate the crowdedness of old patch (trees grow wider crown than they should have) and overestimate the crowdedness of newly created patch 2) With lots of small cohorts understory, it will also cause the crown of large cohort at canopy level to squeeze.
These artifacts will be strong if there is a big difference between min crown area and max crown area. Note: user can eliminate these effects by setting the minimum and maximum crown area to be the same (perhaps the average value), but this disables the perfect plasticity mechanism.