We present results from a field experiment testing the gift-exchange hypothesis inside a tree-
planting firm paying its workforce incentive contracts. Firm managers told a crew of tree
planters they would receive a pay raise for one day as a result of a surplus not attributable to
past planting productivity. We compare planter productivity-the number of trees planted per
day-on the day the gift was handed out with productivity on previous and subsequent days of
planting on the same block, and thus under similar planting conditions. We find direct …