| The aboveground ecological effects of both wildfire and prescribed fire are fairly well characterized while belowground responses of the ecosystem are just beginning to be elucidated. The goal of this study was to determine the effects of low-intensity prescribed fire on soil nutrient dynamics and fine root production and turnover in the top 25 cm of mineral soil in a stand of red pine (Pinus resinosa Ait.) in southern Lower Michigan. The experiment was set up as a randomized complete block, with plots split based on soil depth. Soil and root dynamics were followed over time using a repeated measures analysis. Root characteristics were determined using both coring and minirhizotron techniques and turnover was calculated using several different methods. A new method of calculating fine root turnover, using both production and mortality values as a proportion of average annual standing crop, is proposed. The effects of fire on diameter growth were determined. An additional experiment on the thermal death point of fine roots of red pine was performed to determine if these roots are killed at 60°C, the temperature that is often quoted as the ultimate thermal death point. Contrary to expectations, soil cation concentrations did not increase after fire but rather decreased substantially in both burned and unburned (control) plots; some factor other than fire was controlling nutrient dynamics. Burning also had no effect on fine root production and turnover. However, there were large fluctuations in standing crop of fine roots at different depths. It appeared that soil water availability played a larger role than did fire in controlling root dynamics. The often-observed spring and autumn peaks in root initiation and growth were not seen in this study. Death of fine roots of red pine began at approximately 52.5°C and followed the generally observed patterns of increased mortality with increasing time-of-exposure or with increasing temperature. However, some roots remained alive after being exposed to 60°C, indicating that red pine fine roots may be more thermotolerant than other species and/or tissues. |
