Soil temperature and water content dynamics after disc trenching a sub-xeric Scots pine clearcut in central Sweden

Abstract

Soil scarification is widely used in boreal forestry to promote the growth and survival of seedlings. The aim of the study was to describe and analyze the impact of disc trenching on soil temperature and water content dynamics during the first six growing seasons after clearcutting. The site is a sub-xeric, coarse textured, coniferous field experiment, near Hagfors, central Sweden. Soil temperature and water content were measured hourly both 20 and 45 cm below the original surface of the mineral soil in three types of microsites created by disc trenching (furrows, ridges, and between-furrow areas) and an undisturbed control microsite outside the disc-trenched area. Pinus sylvestris L. seedlings were planted in the furrows and the control area before the measurements. The soil temperature and water content data were analyzed using linear mixed-effect models. Numbers of days exceeding critical thresholds of soil temperature and water content for seedling growth at each microsite were also calculated.Disc trenching increased soil temperature in the topsoil (<20 cm) of the furrows throughout the study period, but the effect declined over time. Similar, but weaker, effects were detected in ridges and between-furrows areas. Likewise, the largest daily and seasonal temperature amplitudes at 20 cm depth were recorded beneath the furrows, and the soil temperature sums (baseline 5 °C) over the whole study period were 20% higher in these microsites than in the control area. Soil temperatures never exceeded values considered optimal for root growth at any of the microsites. The soil water content in the furrows and control area only significantly differed during the last three years, when it was somewhat higher beneath the furrows. During the study period, the total number of days with potential water stress for the planted seedlings (volumetric soil water content <0.09 m3/m3) was 423 in the furrows compared to 554 in the control area. None of the microsites was wet enough to hamper aeration of roots in the topsoil.In conclusion, soil temperature and water regimes were more favorable for the seedlings in the furrows than in the control area for at least six growing seasons. We recommend planting soon after disc trenching to maximize benefits from the improved soil temperature conditions in the furrows.