Effects of disk trench orientation and planting spot position on the ten-year performance of lodgepole pine

A disk-trenching experiment in the sub-boreal spruce zone of central British Columbia, Canada, established three plots (0.12 to 0.26 ha each) with trenches running east-west, and another three plots with north-south trenches. Approximately 200 Pinus contorta Dougl. seedlings were planted in each of 13 microsites: berm, hinge, and trench positions in each of north, south, east, and west aspects, and in untreated locations between furrows. Soil temperature and soil moisture of representative microsites were monitored for 3 years; seedling diameter, height, and vigour were monitored annually for ten growing seasons. Based on tenth-year stem volumes, performance on south-, east-, and west-facing microsites was significantly greater than on north-facing or untreated microsites. Superior growth was noted on all berm and hinge positions other than those facing north. Microsites identified as best in year 5 were also best in year 10. On east-, south- or west-facing berm positions, stem volume averaged 47% to 54% greater than that of control seedlings in year 5, but had suffered greater mortality. Seedlings on east-, south- or west-facing hinges were 46% to 61% (year 5), or 36% to 47% (year 10) larger than control seedlings. Both east-west and north-south disk-trenching treatments are useful for increasing seedling growth, with planting spot selection being more important overall than trench orientation. The stand-level effectiveness of north-south disk trenching was greatest, because the creation of cool north-facing microsites was avoided.