forest operations

[CJ]

I have been using the default crop operations in my SWAT model.

In examining the default mgt operations for deciduous forest (FRSD), I
noticed there are two operations:
'Plant/begin growing season' and 'Harvest and Kill'.

I assume this means that each year trees are planted, then later in
the year they are all chopped down (or perhaps more accurately,
snipped down as they are less than a year old!). This does not reflect
forestry practices in KY.

So I deleted the "Harvest and Kill" operation and applied that change
in operations to all FRSD HRU's, and re-wrote the mgt input files, on
the assumption that this would allow the trees to go into dormancy in
the winter and continue growing the next year.

However, this change has had almost no impact that I can see on the
model's output for a 22 year run (with additional 5 year warm-up). I
had expected mature trees to have a greater impact when compared to
seedlings.

Any ideas what I'm missing?

Thanks,

CJ Johanson

[Jim Almendinger]

CJ -- Check the manual(s) on this.  I'm thinking that forest biomass refers to leaf matter only, and not the entire standing crop of wood.  So, the annual "planting" and "harvesting/killing" really refers only to the leaves.  And, check harvest efficiency for a forest -- it may be essentially zero, meaning all the leaves are left on the landscape, which would be proper, I'd think.  For nutrient balances, you wouldn't want the leafy matter harvested and removed each year.  But -- I haven't really explored all options myself, and would appreciate hearing back when you've explored this a little further.  E.g., how different are the results if you make forests perennial?  It sounds like they operate about the same -- which is probably a good thing. 
-- Jim

Dr. James E. Almendinger
St. Croix Watershed Research Station
Science Museum of Minnesota
16910 152nd St N
Marine on St. Croix, MN  55047
tel: 651-433-5953 ext 19

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