add ability to homogenize the seed pool

[ckoven]

On call today, in discussion of possible ways to understand the nature of the competitive exclusion that dominates PFT dynamics of FATES, one proposal was to try cutting the reproduction-recruitment feedback to decouple recruitment rates from overstory survivorship. that way we can better understand the relative magnitude of competitive exclusion that occurs over an individuals' life from the overall exclusion that occurs. There are (at least) two ways of doing that: (1) seed rain, which already exists in the model, or (2) just homogenize the seed production so that each PFT produces seed mass of every existing PFT in equal proportions. A possible advantage of option 2 is that it is carbon-conservative, whereas option 1 clearly isn't. Option 2 is essentially how they do it in LPJml-FIT (combined wit an arbitrarily large number of PFTs). Anyway it would be nice to play around with this idea, not necessarily as a long-term solution, but to allow us to do some of these experiments to understand the conditions under which exclusion does or does not occur in the model.

[rgknox]

One thing to consider is that eventually we may want to investigate spatial migration of PFTs, ie grid-to-grid over long-time scales. This type of behavior would be influenced by cross-grid seed rain and how prevalent a PFT is in neighboring cells. How we make decisions vis-a-vis 1/2 would impact this type of dynamic.

[ckoven]

@rgknox good point, but I see that as a pretty different issue, as it starts to get into island biogeography type population/metapopulation issues. suggest tabling that for now until we really start to deal with seed dispersal. anyway, what i am proposing is a switch that will default be off for the time being so will not necessarily conflict with whatever we do for seed dispersal.

[rosiealice]

I think #2 sounds doable...

On 26 January 2017 at 16:06, Charlie Koven notifications@github.com wrote:

@rgknox https://github.com/rgknox good point, but I see that as a pretty different issue, as it starts to get into island biogeography type population/metapopulation issues. suggest tabling that for now until we really start to deal with seed dispersal. anyway, what i am proposing is a switch that will default be off for the time being so will not necessarily conflict with whatever we do for seed dispersal.

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[ckoven]

if anyone's interested in playing with this, i pushed up a version that does it on a new branch, https://github.com/ckoven/ed-clm/tree/homogenize_seeds aka commit ac46e0f .