Production physiology of three native shrubs intercropped in a young longleaf pine plantation

The objective of this study was to evaluate how competition would affect the physiology, and thus productivity of American beautyberry (Callicarpa americana L.), wax myrtle Morella cerifera (L.) Small] and inkberry Ilex glabra (L.) A. Gray] when intercropped in a longleaf pine (Pinus palustris Mill.) plantation in the southeastern United States. The effect of competition was assessed via comparisons of mortality, biomass, light transmittance, gas exchange and soil moisture between intercropping and monoculture (treeless) treatments. Overall, shrubs in the intercropping treatment performed worse than those in the monoculture, with higher mortality, and reductions in biomass of 75.5, 50.6, and 68.7% for C. americana, M. cerifera and I. glabra, respectively. Root–shoot ratios for all species were significantly higher and soil moisture during dry periods was significantly lower in the intercropping treatment. Light transmittance below the pine canopy was high (57.7%) and I. glabra was the only species that exhibited reduced A _max when belowground resources were not limiting. These results suggest that the effect of shading is minimal and belowground competition is likely the most important determinant of productivity in this system.