IMPACTS OF SOIL COMPACTION AND TREE STUMP REMOVAL ON SOIL PROPERTIES AND OUTPLANTED SEEDLINGS IN NORTHERN IDAHO, USA

Intensive timber harvesting and site preparation are becoming more com mon as demand for timber-based products increases. On some harvested s ites in the western United States of America and Canada, stump removal is used to ameliorate root disease problems. Soil compaction and nutr ient loss could become a problem on some sites after harvesting, site preparation, or stump removal. In a non-replicated, randomized block e xperiment, two levels of soil compaction (none and severe) and a stump extraction treatment were examined on an ash-cap soil in northern Ida ho. These treatments were planted with Douglas-fir (Pseudotsuga menzie sii var. glauca [Beissn.] France) and western white pine (Pinus montic ola Dougl. ex D. Don) seedlings. Soil compaction increased post-harves t bulk density 15-20% to a depth of 30 cm. Stump removal decreased sur face soil bulk density, but it increased at the 30- to 45-cm depth to levels equal to the soil compaction treatment. One year after outplant ing, seedling top weights were similar among treatments, but root volu me was significantly reduced in the soil compaction treatment. Soil co mpaction and stump removal treatments also reduced the numbers and mor phological types of ectomycorrhizae and non-ectomycorrhizal short root s on Douglas-fir. Western white pine seedlings had reduced numbers of non-ectomycorrhizal short roots in the same treatments. Three years af ter outplanting, stump removal resulted in smaller root collar diamete rs and less total N content for both seedling species. Severe site dis turbance, with associated soil compaction and mixing, may decrease pro ductivity of ash-cap sites by reducing pore space and root and ectomyc orrhizal activity. Managers must weigh short-term benefits of intensiv e site disturbance with possible long-term loss of soil productivity.