Variation of Energy Balance Terms within and between Different Coniferous Forests in Southern Boreal Finland

Three data sets on near surface energy balance terms were collected in the southern boreal coniferous zone in Finland during three winters. Incoming shortwave radiation, incoming longwave radiation and air and ground temperatures were observed with a detailed temporal resolution between October and April. The first data set compares open field and sparse pine forest observations during winter 2007/2008; the second compares sparse and dense canopy location observations in a pine forest during winter 2008/2009 and the third one compares sparse pine and dense spruce forest observations during winter 2009/2010. Differences in incoming PAR radiation between sparse and dense pine canopy locations were also observed at the 1.5m and 15 cm height (at the dwarf shrub level below snow) during winter 2008/2009. The sites were clearly characterized by differing radiation conditions. E.g. for longwave radiation, lowest maximum, minimum and mean values were observed in the open field. The dense pine canopy location received most often more incoming longwave radiation than the sparse canopy location; spruce forest had higher values than pine forest. Clear daily cycle could be seen in the differences in shortwave radiation - this was absent in the longwave radiation data set. Differences were also seen in air and ground temperatures. Ground temperatures were e.g. higher below the dense pine canopy during the snow season, but the ground warmed more below the sparse canopy after snow melt. The pine forest ground temperatures were always higher than the spruce forest ground temperatures. Below the sparse pine canopy, both above and below snow PAR values were most often higher than at the dense canopy site, but PAR radiation was observed through the winter also below the snow at the both sites. The SNOWPACK-model with a canopy module is able to simulate both the below-canopy energy and mass balances and also forest snow structures. The model was applied to detect how the standard canopy parameterization included in the model could reproduce the differences observed between the radiation and temperature data sets. Snow observations carried out in the vicinity of the radiation station were used to validate the quality of SNOWPACK simulations of snow pack structure under different forest canopies. Considering that the amount and type of snow greatly affect the overwintering of ground vegetation in the boreal zone, results of this study suggest that tree and canopy distribution have effects not only on uneven snow and energy distribution, but also more broadly on boreal forest ecosystems.