Canopy gaps are sites of reduced belowground plant competition in a productive old field

Whether small gaps in the aboveground vegetation of productive old fields correspond to gaps in belowground plant biomass, and whether such "root gaps" result in a reduction of competition for soil resources is not known. Our study in an abandoned hayfield shows that root biomass within small gaps (< 0.50 m diam) is 20% of that found within intact vegetation, similar to the findings for shoot biomass. Associated with the decrease in root biomass was a 25% reduction in the intensity of belowground competition within gaps compared to the surrounding matrix vegetation. These differences could not be attributed to variation in soil properties, as gap and matrix soils did not differ in any of the physical or chemical properties measured. These results indicate that the increased plant growth commonly observed within gaps may be partly due to reduced belowground competition, independent of any advantage gained from increased light availability. By providing areas of low belowground competitive intensity, gaps in this field could allow poor belowground competitors to exist with in old fields, thus increasing community diversity.