The plants would still benefit from some air circulation. Passive air circulation doesn't always mean that all of the air will circulate so a small fan will really help with that issue.I'm thinking of building a new cube paludarium around a cool piece of driftwood that I have lying around and am considering setting up the display as an open-topped tank. I'm not planning on having frogs in this setup but I would like some broms, orchids, tillandsias and other epiphytes.
Even with water in the bottom of the setup, the humidity will be a lot lower in an open topped tank. I imagine this will be fine for tillandsias. Any suggestions for mini orchids, broms and other epiphytes that would would do well in this setting?
Also, I know that many of these plants appreciate some air circulation in a more sealed viv. Would an open-topped setup provide enough passive air movement that additional fans are unnecessary?