A Viking with enough trees will prosper. Vikings need trees to build their boats and homes, and they flourish when they have enough.
Vikings knew that in order to prosper they also needed to collect acorns (えい). If you're chopping down trees all the time, you need to actively grow them back too. That's why acorns are the actual, secret key to Viking prosperity.
Currently there are no similar looking kanji which exist in the WaniKani learning system