Influence of harvest residues and vegetation on microsite soil and air temperatures in a young conifer plantation

Abstract

Soil temperature influences many processes in young forest stands including growth and phenology of trees, water uptake, and nutrient mineralization. Effects of harvest residue management and other site preparation techniques on soil and air temperatures have previously been reported at the treatment level, but there is little information on temperature patterns in the various microsites created by these treatments. This study examines the effects of bole-only harvesting with and without vegetation control (BO + VC; BO − VC) and total-tree harvesting plus removal of legacy woody debris with vegetation control (TTP + VC) on microsite temperature in a young Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) plantation. Hourly soil temperatures were recorded at a 10-cm mineral soil depth for 5 years post-planting, and near-ground (25 cm) air temperatures were recorded for 1 year. In the TTP + VC treatment, mean soil temperature and diurnal range in soil temperature during the growing season differed by microsite surface condition in the following sequence: exposed mineral soil > intact forest floor > decaying wood over soil > shade of stumps. In the BO treatments, soil temperature differences among microsites were smaller, and only the stump-shade microsite differed significantly from the others. Near-ground air temperature did not differ by microsite. A sine-wave model showed that diurnal warming of soil beneath decaying wood occurred more slowly than for other microsites. Total annual soil degree-day accumulation was 25–37% greater in the TTP + VC treatment than in the BO + VC treatment; the greatest difference occurred in the year with the warmest spring air temperature. Vegetation control treatments had little effect on soil temperature in the BO harvest treatment. The reduced microsite variability and diurnal fluctuation in soil temperature in the BO harvest treatment may be beneficial where summer temperature extremes are a concern. Alternatively, the warmer spring and early summer soil temperatures of the TTP harvest treatment may be advantageous for early seedling development.