Impacts of soil compaction and tree stump removal on soil properties and outplanted seedlings in northern Idaho, USA

Abstract

Intensive timber harvesting and site preparation are becoming more common as demand for timber-based products increases. On some harvested sites in the western United States of America and Canada, stump removal is used to ameliorate root disease problems. Soil compaction and nutrient loss could become a problem on some sites after harvesting, site preparation, or stump removal. In a non-replicated, randomized block experiment, two levels of soil compaction (none and severe) and a stump extraction treatment were examined on an ash-cap soil in northern Idaho. These treatments were planted with Douglas-fir (Pseudotsuga menziesii var. glauca [Beissn.] Franco) and western white pine (Pinus monticola Dougl. ex D. Don) seedlings. Soil compaction increased post-harvest bulk density 15-20% to a depth of 30 cm. Stump removal decreased surface soil bulk density, but it increased at the 30- to 45-cm depth to levels equal to the soil compaction treatment. One year after outplanting, seedling top weights were similar among treatments, but root volume was significantly reduced in the soil compaction treatment. Soil compaction and stump removal treatments also reduced the numbers and morphological types of ectomycorrhizae and non-ectomycorrhizal short roots on Douglas-fir. Western white pine seedlings had reduced numbers of non-ectomycorrhizal short roots in the same treatments. Three years after outplanting, stump removal resulted in smaller root collar diameters and less total N content for both seedling species. Severe site disturbance, with associated soil compaction and mixing, may decrease productivity of ash-cap sites by reducing pore space and root and ectomycorrhizal activity. Managers must weigh short-term benefits of intensive site disturbance with possible long-term loss of soil productivity.