Root production and herbivory in an upland grassland community in Yellowstone National Park

Few investigations have been conducted on belowground consumption and production relative to studies of aboveground processes, due to the difficulty of examining root systems over time without significant disturbance.  Additionally, most field studies of root dynamics are conducted at one month time steps, an interval that may miss a significant proportion of the rapid production/mortality dynamics of fine roots.    The purpose of this study was to estimate rates of root production and consumption in an upland grassland in Yellowstone National Park. Root lengths were imaged in four minirhizotrons, four times per month (at three-day intervals over ten days) from May - September, 2005.  We attributed root length that disappeared over each three-day period as primarily due to root herbivory.  Average production per day (mm of root length) was approximately five times greater in May and June as compared to July, August, and September. Average daily consumption was not significantly different among months and was approximately 0.5% of the total root length.  Temporal and spatial (depth) fluctuations in the rates of production and consumption were likely related to seasonal variations in soil moisture content.  A comparison of rates derived from sampling at three-day and one-month increments revealed that month to month sampling underestimated consumption by approximately 100% and elongation by 150%.  This study highlights the often overlooked importance of root herbivory in grassland communities and the need for sampling roots at a time step that is short enough to match the temporal scale of root dynamics.