Projected decrease in wintertime bearing capacity on different forest and soil types in Finland under a warming climate

Abstract

Abstract. Trafficability in forest terrain is controlled by ground-bearing capacity, which is crucial from the timber harvesting point of view. In winter, soil frost affects the most the bearing capacity, especially on peatland soils which have in general low bearing capacity. Ground frost similarly affects the bearing capacity of forest truck roads. A 20 cm thick layer of frozen soil or 40 cm thick layer of snow on the ground may already be sufficient for heavy forest harvesters. In this work, we studied the impacts of climate change on soil frost conditions and, consequently, on ground-bearing capacity from the timber harvesting point of view. The number of days with good wintertime bearing capacity was modelled by using a soil temperature model with a snow accumulation model and wide set of downscaled climate model data until the end of the 21st century. The model was calibrated for different forest and soil types. The results show that by the mid-21st century, the conditions with good bearing capacity will decrease in wintertime in Finland, most likely by about 1 month. The decrease in soil frost and wintertime bearing capacity will be more pronounced during the latter half of the century, when drained peatlands may virtually lack soil frost in most of winters in southern and western Finland. The projected decrease in the bearing capacity, accompanied with increasing demand for wood harvesting from drained peatlands, induces a clear need for the development of sustainable and resource-efficient logging practices for drained peatlands. This is also needed to avoid unnecessary harvesting damages, like rut formation on soils and damage to tree roots and stems.

Thermal seasons in northern Europe in projected future climate

“…The prolongation of thermal summers acts to increase the number of days with a high risk of wildfire ignition . The shortening of thermal winters deteriorates the preconditions of timber harvesting and transportation of timber in forest truck roads, since the lack of ground frost weakens ground-bearing capacity (Lehtonen et al, 2019).…”

Timber extraction by cable yarding on flat and wet terrain: a survey of cable yarder manufacturer’s experience

“…Furthermore, the duration of the frozen ground period is getting shorter every year in most regions of the globe (e.g. in Finland; Lehtonen et al 2019), which makes it increasingly urgent to find new harvesting solutions. Manufacturers of ground-based solutions seek to lower the impact of machine traffic on soils by enlarging the contact area between machine and soil through adapting tyre pressure, hydro-pneumatic suspension (e.g.…”

The 10-Year Return Levels of Maximum Wind Speeds under Frozen and Unfrozen Soil Forest Conditions in Finland

“…where T t Z ( • C) is the soil temperature on a previous day, T AIR ( • C) is the air temperature, ∆t is the length of a time step (s), K T (W m −1 • C −1 ) is the thermal conductivity of the soil above Z S , C S (J m −3 • C −1 ) is the specific heat capacity of the soil above Z S , C ICE (J m −3 • C −1 ) is the specific heat capacity due to freezing and thawing, f S (m −1 ) is an empirical damping parameter due to snow cover, D S (m) is snow depth, K T,LOW (W m −1 • C −1 ) is the thermal conductivity of the soil below Z S , C S,LOW (J m −3 • C −1 ) is specific heat capacity of the soil below Z S , and T LOW ( • C) is soil temperature at the depth of Z l . Following to [31], Z l was set to 6.8 m.…”

“…By using soil temperature observations from several stations across Finland, the soil temperature model was parametrized for three different soil types: clay or silt soil, sandy soil, and peatlands [31]. Between the depths of 20 and 100 cm, the parametrized model explained approximately 90-99% of the observed variability in soil temperatures.…”

“…In the above context, the objective of this study was to produce spatially detailed estimates (maps) of the 10-year return level maximum wind speed under current climate for unfrozen and frozen soil conditions in some of the most common combinations of forest and soil types in Finland. By utilizing soil frost calculations of [31] to determine the duration of soil frost seasons, the wind speed return level calculations were done for dense Norway spruce stands on clay or silt soil, Scots pine stands on sandy soil, and Scots pine stands on drained peatland. The coarse resolution estimates of the 10-year return level of maximum wind speed were based on 1979-2014 ERA-Interim dataset [32].…”