Temporal heterogeneity of soil moisture in grassland and forest

Abstract

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.