Let's assume the following:
An adult white dragon has been caught by a powerful group of LE wizards. Somehow they managed to trap it inside the depths of their underground laboratories, snaring it into a prison cell, perpetually harvesting scales, blood, teeth and whatever else they deemed useful.
Going by the description of suitable locations for a White dragon’s lair (MM, page 102) deep subterranean chambers (i.e. its prison cell) would fit its taste; at least if it had the choice to settle there.
Assuming the dragon can't escape, can't just choose to die or kill itself and "lives" in its prison for some extended period of time (years, decades, centuries?), would the regional effects characteristic to its lair manifest?
The region containing a legendary white dragon's lair is warped by the dragon's magic, which creates one or more of the following effects:
To me the wording of the MM leans towards the effects being a passive thing, but it's not clearly stated anywhere, far as I am aware.
Does a legendary dragon have to will the regional effects around its lair into existence or is it a passive effect caused simply by their presence?