Rough handling, soil temperature, and root development in outplanted Sitka spruce and Douglas-fir

Abstract

Sealed bags containing forty 2-year-old Sitka spruce (Piceasitchensis (Bong.) Carr.) transplants were dropped 1–15 times from a height of 3 m onto a hard floor. A single drop reduced root growth potential of the plants as measured by a 10-day test, although after 18 days' growth the effect was no longer detectable. Dropping the bags 5 or 15 times severely decreased root growth potential even in the 18-day test. The 15-drop treatment significantly depressed 1-year survival of samples planted in the nursery. Sitka spruce and Douglas-fir (Pseudotsugamenziesii fMirb.) Franco.) transplants dropped 10 times, together with control plants, were placed in root observation boxes with an air temperature of 8 °C and a soil temperature of 4, 8, 12, or 16 °C. At 4 °C soil temperature, little or no root growth was observed in either species. At the higher temperatures the total numbers of new roots formed in 10 days and the number of new roots greater than 1 cm in length formed in 18 days were generally greater in Sitka spruce than Douglas-fir. In both species, root growth was sharply reduced by the mechanical shock treatment. Dropping the trees also depressed mycorrhizal development and resulted in a significant lowering of predawn water potential in Douglas-fir.