Numerous studies have demonstrated biodiversity–productivity relationships in plant communities, and analogous genetic diversity–productivity studies using genotype mixtures of single species may show similar patterns. Alternatively, competing individuals among genotypes within a species are less likely to exhibit resource-use complementarity, even when they exhibit large differences in their effects on ecosystem function. In this study, we test the impact of genotype diversity and genetic identity on ecosystem function using an ecosystem-scale common garden experiment. Distinct tree genotypes were collected across the entire natural range of the riparian tree Populus fremontii in the USA, and grown in 1–16 genotype combination forest stands. Due to the warm climate and irrigation of the planting location along the Colorado River (AZ, USA), mature forest physiognomy with trees up to 19 m tall was achieved in just five years. Several key patterns emerged: (i) genotype richness did not predict forest productivity, suggesting a lack of net biodiversity effects; (ii) we found differences among genotype monoculture stands comparable to differences in average productivity across all forest biomes on Earth; (iii) productivity was predicted based on genetic marker similarity in trees; (iv) genetic-based differences in leaf phenology (early leaf-on and late leaf-fall timing) were correlated with >80% of the variation in tree and forest productivity irrespective of home-site conditions. Large differences in productivity among genotypes can result in dramatic differences in forest productivity without resulting in diversity–productivity relationships that are present in species-scale biodiversity studies.

Raw data for tree sizes, blocks, and treatments in the Cibola Tree Genetics and Productivity ExperimentThis file contains the raw data for the sizes of trees in the Cibola tree genotype diversity and productivity experiment. Treatments and block locations are also indicated.Cibola_2012_tree_data_raw.csvhomecibolaThis data file contains data on the home sites where genotypes were collected for the Cibola tree genotype diversity and productivity experiment. Tree leaf phenology data is also included (higher scores reflect greater leaf-off times over the course of a year).Cibola microsatellite marker dataThis file contains the microsatellite marker data for the Cibola genotype diversity and productivity experiment.Cibola.markerdata.csv