Abstract. Sediment transport activities in periglacial environments
are controlled by microclimate conditions (i.e., air and ground temperatures,
throughfall), which are highly affected by vegetation cover. Thus, there is
the possibility that forest harvesting, the most dramatic change to
vegetation cover in mountain areas, may severely impact sediment transport
activities in periglacial areas (i.e., soil creep, dry ravel). In this study,
we investigated changes in sediment transport activities following forest
harvesting in steep artificial forests located in a humid periglacial area of
the southern Japanese Alps. In the southern Japanese Alps, rainfall is
abundant in summer and autumn, and winter air temperatures frequently rise
above and fall below 0∘. Our monitoring by time lapse cameras
revealed that gravitational transport processes (e.g., frost creep and dry
ravel) dominate during the freeze–thaw season, while rainfall-induced
processes (surface erosion and soil creep) occur during heavy rainfall
seasons. Canopy removal by forest harvesting increased the winter diurnal
ground surface temperature range from 2.7 to 15.9 ∘C. Forest
harvesting also increased the diurnal range of net radiation and ground
temperature, and decreased the duration of snow cover. Such changes in the
microclimate conditions altered the type of winter soil creep from frost
creep to diurnal needle-ice creep. Winter creep velocity of ground surface
sediment in the harvested site (> 2 mm day−1 on the days
with frost heave) was significantly higher than that in the non-harvested
site (generally < 1 mm day−1). Meanwhile, sediment flux on
the hillslopes, as observed by sediment traps, decreased in the harvested
site. Branches of harvested trees left on the hillslopes captured sediment
moving downslope. In addition, the growth of understories after harvesting
possibly reduced surface erosion. Consequently, removal of the forest canopy
by forest harvesting directly impacts the microclimate conditions (i.e.,
diurnal range of ground temperature and net radiation, duration of snow
cover) and increases frequency and velocity of periglacial soil creep, while
sediment flux on hillslopes is decreased by branches left on the hillslopes
and recovery of understories. The impact of forest harvesting on sediment
transport activity is seasonally variable in humid periglacial areas, because
microclimate conditions relevant to both freeze–thaw processes and
precipitation-induced processes control sediment transport.
Forest harvesting impacts on micrometeorological conditions and
sediment transport activities in a humid periglacial environment
