Temporal heterogeneity of soil moisture in grassland and forest

1 Differences between growth forms in the spatial heterogeneity of associated soil resources, such as water, are well-documented. We tested for differences in the temporal heterogeneity of soil moisture between natural grassland, shrubland and Populus tremuloides forest at the northern edge of the Great Plains. 2 Weekly measurements of soil moisture over a year, and daily measurements during a growing season, both showed significant interactions between habitat and time. Soils under grassland and shrubs were wettest at the start of the growing season but driest at the end. 3 The coefficient of variation of soil moisture content over time during the growing season was significantly higher in grassland than in forest. Similar results were found for whole-year measurements, and at two depths beneath the soil surface (10 and 30 cm). 4 We found little interception of rainfall in any vegetation type. The net effect of vegetation on soil moisture during a drying period, however, was significantly greater in grassland than in forest, suggesting that differences in the temporal heterogeneity of soil moisture content are related to resource uptake.