Soil biological activity in recent clearcuts in west-central Alberta

Soil biota response to changes in the soil physical environment following forest harvesting is relatively unknown in boreal forests. Soil biological activity was measured at four sites with Luvisolic soil following clear-cut forest harvesting. Aerobic respiration rate and cellulose decomposition in flooded soils were measured on soil samples collected from treatment plots subjected to tree removal only and tree removal associated with three levels of skidding activity immediately after clear-cut harvesting and after 1 and 2 yr. More than half of variation in respiration and cellulose decomposition rates was related to soil properties. Soil respiration rate increased significantly after 1 yr but was not affected by skidder traffic. Cellulose decomposition was highest in soil with air-filled porosity <0.10 m(3) m(-3), and increased significantly with skidder traffic. Air-filled porosity measured in the field at the time of harvest indicated a poorly aerated environment that becomes wetter in subsequent years. The results imply that soil had biota well adapted to poor soil aeration. The development of a fully anaerobic soil environment following forest harvesting only occurred on compacted soil after heavy precipitation, but partial anaerobiosis of these boreal forest soils was common. Although partial anaerobiosis increased decomposition rate, it is considered sufficient to adversely affect the growth of plant roots and change the availability and mobility of nutrients.