Soil heterogeneity effects on canopy structure and composition during early succession

Early succession from annuals to herbaceous and woody perennials on abandoned fields and grasslands is marked by vegetation heterogeneity; i.e., variation in canopy composition and structure over the field through time. Soil resource heterogeneity could promote vegetation heterogeneity. We created soil resource patchiness on two newly ploughed fields by establishing two types (fertilized, unfertilized) of checkerboard plots with two, four, or eight subplots (trenched, untrenched) to test effects of soil fertility heterogeneity scale on vegetation heterogeneity during early succession. Canopy composition and structure were censused in years 2, 4 and 6. On both fields, soil resource heterogeneity did not affect canopy composition or structure. Differential abundance of dominant species, Ambrosia trifida on one field and Solidago altissima on the other, between fertilized and unfertilized plots led to decreased vegetation heterogeneity among subplots within plots and increased vegetation heterogeneity among plots. Soil enrichment promoted taller and layered, but species-poor, canopy. In general, soil fertility effects on abundance, expansion, and dominance of individuals of dominant species promoted variation in canopy composition and structure, or vegetation heterogeneity, among plots on the two fields.