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DrylandEcology / SOILWAT2

An ecosystem water balance simulation model
GNU General Public License v3.0
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Biomass CO2-effect in trees: no increase in total biomass? #94

Open dschlaep opened 6 years ago

dschlaep commented 6 years ago

Commit 69da0d9ef842e6b89cccb22fbb00b95738b36a3b:

The function SW_VPD_init applies biomass CO2-effects for grasses, forbs, and shrubs to total biomass and keeps percent-live constant to calculate live biomass. Thus, total and live biomass increase with higher CO2 concentrations.

For trees, the biomass CO2-effect is applied to percent-live while total biomass is kept constant. Thus, only live but not total biomass increases with higher CO2 concentrations.

@jbbradford Is this really want we want? Shouldn't total tree biomass be incremented by the gain in live biomass?

  CO2 (ppm) Biomass CO2-effect WUE CO2-effect Tree biomass (g/m2) Tree live biomass (g/m2) Tree live (%) Grass biomass (g/m2) Grass live biomass (g/m2) Grass live (%)
1980 338 0.976 1.019 15000 1406 0.094 179 50 0.281
1981 340 0.977 1.017 15000 1409 0.094 179 50 0.281

... 2009 | 387 | 1.023 | 0.949 | 15000 | 1474 | 0.098 | 188 | 53 | 0.281 2010 | 389 | 1.025 | 0.946 | 15000 | 1477 | 0.098 | 188 | 53 | 0.281

dschlaep commented 6 years ago

John:

My impression from reading the CO2 literature was that it was foliage biomass (well, really LAI) that reliably responded to CO2. So we did intend for this effect to only influence the live biomass (how we represent foliage biomass in trees) for that functional group. While it may be that total biomass also responds, I'm not sure we have CO2 enrichment studies long enough to quantify those effects in long-lived woody plants.

dschlaep commented 1 year ago

see answer in https://github.com/DrylandEcology/SOILWAT2/issues/330