Ultima Online Five on Friday Q&A

EA's Jeremy Dalberg brings us another installment to his Ultima Online Five on Friday Q&A series.
"For us learning impaired, what causes a resource field to change? Say, ore zones. Does the zone need to be worked, or is there a chance it will change when it is "refreshed" without it even being touched?"

There are two ways for ore (or wood) zones to refresh: when the zone is mined (not necessarily mined out, just mined,) it has a chance to reroll its resource type. At this point, it sets a timer. After that timer is up, the next time it is mined, it has a chance to reroll again. (The timer prevents it from cycling too fast.) The second way is a general chance that affects the entire subserver, and that is unpredictable - so even if a vein is never mined, it may still switch ore types from time to time.