The IDENT trial at Sault Ste. Marie (ON), established in 2013, examines how soil moisture availability influences species growth in mixtures and monocultures.
Six native North American tree species were planted as monocultures, and two, four and six species mixtures in 176 plots. All combinations were treated with irrigation or drainage.
Irrigation had a positive effect on aboveground biomass and growth of most species in both years. Species diversity and type of mixture had significant effects on biomass production. Shade intolerant species biomass increased in mixtures that are more diverse. In more shade tolerant species growth was reduced in mixtures compared to monocultures. One mid tolerant species was largely unresponsive to mixture or richness. These differences were exacerbated in drier years, where shade intolerant species showed higher biomass in irrigated and more diverse mixtures, contrary to the other species.