PnET for LANDIS and soils

[Brian Miranda]

I have been using the PnET-II for LANDIS-II tool to calculate establishment probabilities (Pest) and ANPP values in an area that has variable soil textures including some very sandy soils.  I am concerned that the Pest estimates are not strongly influenced by the soil water holding capacity (WHC), which is one of the site input parameters in the PnET for LANDIS tool.  I am curious if other users have been satisfied with the influence of WHC on Pest using this tool.  The impact of WHC on growth (ANPP) appears to be much stronger and more reasonable than it is for Pest.

I have conducted a sensitivity analysis using the PnET for LANDIS tool by estimating Pest and ANPP for sugar maple on a generic site varying only the WHC parameter.  I have attached output files for the 2 extremes that I ran (WHC = 1cm, WHC = 35cm).  I would appreciate any feedback from other users.  You can see a noticeable drop in ANPP when WHC gets very low, but the drop in Pest is not as much as I would expect.  I would basically expect Pest for sugar maple to drop to 0 at some level of low WHC.  The other thing that jumps out at me is the negative values for NEP (Net Ecosystem Productivity).  Negative values don't make sense to me for that, but perhaps I am misinterpreting what that represents.

I will appreciate any insights that others have learned using this tool. Perhaps there are some species parameters that I should be looking at to increase the sensitivity to water stress.  If anyone can provide guidance on this issue, please let me know.

Thanks!

-Brian

[Brian Miranda]

A brief update:  My earlier results were based on allowing CO2 fertilization and effect on stomata conductance.  I have experimented with turning off the 'CO2 EFFECT On Photosynthesis' and the 'CO2 EFFECT On Stomata conductance', and see almost no difference in the results in regards to establishment probabilities.  There are some differences in ANPP values, but not establishment.

Any other suggestions for what I might be missing?

Thanks,

-Brian

[Xi, Weimin]

Hi Brian,

When you said that you allowed CO2 fertilization, did you use increased CO2 concentration (e.g., A1fi) over your simulation period in your climate files? Based on our group's experience, using increased CO2 concentration (with CO2 fertilization effect) or using constant CO2 concentration (without CO2 fertilization effect) could make a quite some difference on both PEST and ANPP.

One thing I noted that your .out file only showed the results for 1961-1999. For the PnET-II for LANDIS-II tool, normally I only used this period for spinup and mainly look at the PEST and ANPP after spinup period (after 2000, or 2100).

Another thing is that,  the WHC values you tested/used may be indeed too extreme. The values in N WI and UP MI we got based on the soil data varied from 10-25 cm. I guess a complete sensitivity analysis using all possible WHC values may help us to get a better understanding on the performance of the PnET-II. 

Cheers,
Weimin

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[Weimin Xi]

Hi Brian,

When you said that you allowed CO2 fertilization, did you use increased CO2 concentration (e.g., A1fi) over your simulation period in your climate files? Based on our group's experience, using increased CO2 concentration (with CO2 fertilization effect) or using constant CO2 concentration (without CO2 fertilization effect) could make a quite some difference on both PEST and ANPP.

One thing I noted that your .out file only showed the results for 1961-1999. For the PnET-II for LANDIS-II tool, normally I only used this period for spinup and mainly look at the PEST and ANPP after spinup period (after 2000, or 2100).

Another thing is that,  the WHC values you tested/used may be indeed too extreme. The values in N WI and UP MI we got based on the soil data varied from 10-25 cm. I guess a complete sensitivity analysis using all possible WHC values may help us to get a better understanding on the performance of the PnET-II. 

Cheers,
Weimin

[Brian Miranda]

Hi Weimin,

Thanks for your feedback.  The evaluation I am trying to do here is meant to represent our baseline "no climate change" scenario, so I am using the recent historical period (1961-1999) to estimate Pest and ANPP.  In this case, the CO2 levels I used where based on historical values (Moana Loa).  I probably should extend the climate and CO2 ranges up to current (at least 2010), but that won't likely change the output relative to WHC.  When it comes to estimating Pest and ANPP for our climate change scenarios, I do intend to use projected CO2 concentrations along with the climate projections.  But my goal with this current evaluation is to first make sure the spatial patterns due to differences in soils make sense under the current climate before adding the complication of climate change.  In regards to the range of WHC values, I have looked at the SSURGO data for our study area (Northeast Sands ecoregion in WI) and see values ranging 0-44 cm, so the range I am evaluating is quite relevant.  I'm still doing some additional digging into the code to figure out what's happening, and I'll post any significant findings.  In the meantime, I'll appreciate any additional feedback.

Cheers,

-Brian