Overyielding in young tree communities does not support the stress-gradient hypothesis and is favoured by functional diversity and higher water availability

Summary:

Biodiversity effects on productivity and other ecosystem functions are strongly dependent on climate and resource availability. Based on the stress-gradient hypothesis, under conditions of greater abiotic stress, diversity effects on plant performance are intensified due to the increased relative importance of positive plant interactions. However, whether this hypothesis is consistently applicable in forest systems remains unclear. A field trial was established to test the stress-gradient hypothesis and examine diversity effects on aboveground biomass production of young trees in mixtures exposed to different water availability.
Six native tree species of northern temperate forests (Acer saccharum, Betula papyrifera, Larix laricina, Picea glauca, Pinus strobus, and Quercus rubra) were planted as monocultures and as mixtures of two, four, and six species. For five growing seasons, four replicates of each community were exposed to conditions of either low- or high-water a...