Change driver data for under-canopy PFT in mixed systems

[dlebauer]

This is an idea to consider that came up in a meeting. Capturing here for consideration.

When adding herbaceous ground cover to orchard, reduce solar radiation in met driver data during data prep step as a way of simulating orchard canopy shade.

Considerations:

• This is a very coarse approximation - it does not capture e.g. moisture, temperature, actual canopy cover
• It may not be necessary if tuning mixing ratios is sufficient to capture effect direction
• Seems straightforward to implement, but may be difficult to calibrate / tune.
• Our focus is on developing the overall workflows that could be later adapted to support models with multi-pft support.

[dlebauer]

I am closing as "wontfix"; going with "tuning mixing ratios to capture effect direction" until / unless that is insufficient. But will likely be sufficient to meet objective of capturing effect direction.