Data from: Individual size inequality links forest diversity and above-ground biomass

1. Despite the mounting evidence for positive diversity–productivity
relationships found in controlled experiments, diversity effects on
productivity in natural systems remain hotly debated. Understanding the
multivariate links between diversity and productivity in natural systems,
in particular natural forests that host the majority of terrestrial
biodiversity and provide essential services for humanity, remains a
critical challenge for ecologists. 2. We analyzed data from 448 plots of
varying tree species diversity, stand ages, and local nutrient
availability in Canada's boreal forest (52°30’ – 55°24’ N latitude
and 102°36’ – 108° W longitude). We used structural equation models to
link multivariate relationships between above-ground biomass, tree species
diversity, stand age, and soil nutrient availability. 3. Above-ground
biomass increased with diversity indirectly via increasing tree size
inequality, and increased with stand age and was higher on sites of medium
soil nutrient regime directly as well as indirectly via increased tree
size inequality. 4. Synthesis. Our results demonstrate positive diversity
effects on above-ground biomass in natural forests of diverse forest ages
and soil resource availability. Furthermore, we show that tree size
inequality acts as a mechanism for the positive diversity effects on
above-ground biomass, and as a mechanism in regulating above-ground
biomass and species diversity simultaneously via interactions among
individuals in natural forests.