Where to build markets - only in fertile lands?

[al Roumi]

The easiest first:

"global", as in for my clan........?

yes.

so why do some provinces complain about lack of food and not others, considering both have the first stone castle and the -2 market upgrade?

Did you check the unrest before your food supply went throught he floor? It's possible food shortages add global/faction wide unhappyness factor. So your most unruly provinces are the most likely to complain/revolt under food shortages.

i don't like it, i want to max out a tree if i go to the trouble of investing in it. :(

Embrace it! Tough decisions are what make the game challenging and interesting. You can squeeze more repeat campaigns out of different approaches too :)