Parameters in Plant (plants.plt) - meaning of plnt_pop

[Maarten J. Waterloo]

Hello,

There are several parameters in plant.plt that determine initial plant status. Some of these are clear, but I cannot find out what the Plant population (plnt_pop) parameter does. I use this for a forest in SWAT+. The default value of the plant population is 0, does that mean that no plant population is present? Should the value then be 1 to indicate that there is a plant population?  It would be nice if a description of this value can be given.Does anyone know what the parameter does? Thanks!

Maarten Waterloo

[Willem Vervoort]

Hi Maarten, 

I don't know the exact answer. However, all the examples in the SWAT+ I/O document have 0 for plant population: https://swatplus.gitbook.io/docs/user/io (p211 or p7 in Chapter 3)

I also have used 0. I found that the initial LAI and setting plants growing to yes did the main job. However, you should also check that the community values are correct, even if you use the default crops in SWAT+, I found strange things for most of the perennial species.

Hope this helps

Willem

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[Maarten J. Waterloo]

Hi Willem,

Thanks for your reply. I also tried to find the plnt_pop parameter in the source code in plant related files, but could not find anything. For now, I'll just leave it at zero. We have much lower evaporation values for forest then for grass and we are trying to find out why this happens.  First we had the year_mat parameter (years to maturity) at zero, which caused a low ET of only several mm per year. I would think that growth would happen and ET would increase in time but it did not over 25 years period. Setting this parameter to 1.0 did increase the evaporation but in my opinion it is still too low, so now we are looking for other options. We use communities of Forest Evergreen Needleleaf (foen), Forest Mixed (fomi) and Forest Deciduous Broadleaf (fodb) with default values from the plant database and these all behave similarly, with ET about 50% of that of grass. We use management schedules to plant on day 1 of the simulation and no further management. If you have any other suggestions, these would be welcome.

Regards,

Maarten

Op zondag 21 maart 2021 om 00:50:58 UTC+1 schreef Willem Vervoort:

[Willem Vervoort]

Hi Maarten,

I haven't done much with SWAT+ for a while. but attached is my plants database: https://drive.google.com/file/d/1UrP-MKBiXVpovwsQWR2Lpdx2iKZsNkWx/view?usp=sharing

I have "euca" as a perennial forest, but I have not checked in detail whether it is growing correctly. I also have years_mat = 0, because then it uses heat units, but I started off in the plant community with a population that is 5 years old.

Not sure if that helps. When I find time this year I plan to get back to SWAT+, sorry.

Willem

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[Maarten J. Waterloo]

Hi Willem,

Thanks!

Regards,

Maaren

Op maandag 22 maart 2021 om 11:08:54 UTC+1 schreef Willem Vervoort:

[Alexander N.]

Hello Maarten,

were you able to get some more insight in this parameter in the meantime?

Best regards

Alex