Effects of Migratory Grazers on Spatial Heterogeneity of Soil Nitrogen Properties in a Grassland Ecosystem

Large herbivores are known to respond to spatial heterogeneity in the distribution of forage resources, but how important herbivores are in creating those spatial patterns, how their influence may be scale dependent, and how herbivore-induced patterns affect ecosystem processes remain unclear. We examined the effects of native migratory ungulates on the spatial distribution of soil nitrogen and N-mineralization potential at scales ranging from 0.1-30 m in grasslands of Yellowstone National Park using geostatistical analyses of soils collected inside and outside long-term (36+-yr) exclosures. At small spatial scales (0.1-2 m), ungrazed grasslands showed a high degree of patch-iness in the distribution of soil N and N-mineralization potential (94% and 77% of sample variation explained by small-scale patchiness, respectively). For both variables, patches occurred at a consistent mean size of ∼40 cm. In contrast, grazed grassland exhibited minimal spatial structure in the distribution of soil N and N-mineralization rates (