User blog comment:Dark Paladin X/Dark Paladin X Civ Crafting Corner: The Khmers/@comment-27023515-20161010113016/@comment-27023515-20161010201723

Which, in effect, increases the gather rate. He gathers 20 food, drops off 24, so he's effectively gathering 24 food in the time normal farmers gather 20 food. If you just want them to get more resources out of a tree/farm, you're looking at the mayan bonus (but that one wouldn't make any sense with trade).