Effect of vegetation on snow cover at the northern timberline: a case study in Finnish Lapland

Abstract

The presence of permanent snow cover for 200-220 days of the year has a determining role in the energy, hydrological and ecological processes at the climate-driven spruce (Picea abies) timberline in Lapland. Disturbances, such as forest fires or forest harvesting change the vegetation pattern and influence the spatial variation of snow cover. This variability in altered snow conditions (in subarctic Fennoscandia) is still poorly understood. We studied the influence of vegetation on the small-scale spatial variation of snow cover and wind climate in the Tuntsa area that was disturbed by a widespread forest fire in 1960. Radar was applied to measure snow thickness over two vegetation types, the spruce-dominant fire refuge and post-fire treeless tundra. Wind modelling was used to estimate the spatial variation of wind speed and direction. Due to the altered surface roughness and the increased wind velocity, snow drifting was more vigorous on the open tundra, resulting in a 30-cm thinner snow cover and almost half the water equivalent compared to the forest values. The changes in local climate after the fire, particularly in snow cover, may have played an important role in the poor recovery of vegetation: a substantial area is still unforested 40 years after the fire.

Community Structure, Biodiversity, and Ecosystem Services in Treeline Whitebark Pine Communities: Potential Impacts from a Non-Native Pathogen

“…Watershed studies in arid, western plant communities indicated that strategically-placed snow fences increased snow accumulation, snowmelt discharge and the length of the flow period ( [65] and references therein). Subsequent subalpine and treeline forest observational studies verified that snow depth is positively associated with tree distribution, as observed for snow fences [43,[66][67][68][69][70] (Figure 6, Table 4). Snow depth influences other hydrological processes, including snow water equivalent (SWE), runoff initiation date, snow cover season length, and the spatial pattern of snow disappearance [41,[69][70][71][72] (Table 4).…”

“…[58,[60][61][62] Field measurements demonstrate increased snow accumulation, snow depth, and snow water equivalent leeward of trees. [42,[66][67][68][69]80] Increased snow depth positively correlates with snow water equivalent (SWE). [69,70] Increased snow depth is associated with delayed runoff initiation and longer snow persistence.…”

“…[42,[66][67][68][69]80] Increased snow depth positively correlates with snow water equivalent (SWE).…”

“…Trees within the ATE help determine snow spatial distribution across the landscape by increasing snow depth in their lee [42,62,67,68,80]. Snow depth affects snowpack characteristics, including SWE, timing of snowmelt initiation and runoff, and snow disappearance dates [42,58,62,70,73,80].…”

Observed cold season changes in a Fennoscandian fell area over the past three decades

“…In addition to snowfall, snow depths in a certain location are determined by redistribution by wind and aging and melting processes in accumulated snow. The study of Vajda et al (2006) in the same geographical region showed that more vigorous snow drifting on the open tundra with low vegetation resulted in 30-cm thinner snow cover and almost half the water equivalent compared to the forest values. We found negative trends in snow depths in the Värriö weather station located in the , not significant) in relation to September-October AO and January SCA values coniferous forest zone, mixed forest, and mountain birch forest, whereas snow depth in the mountain heath did not change significantly during the study period.…”