PS 25-71
Different responses of boreal understory vegetation after 1 versus 11 years of snow removal
Boreal forests make up one third of the world’s forested areas and store 30% of the global terrestrial carbon pool. They are shaped by distinct seasonality with a persistent snow cover during wintertime. However, the extent and duration of snow cover are expected to decrease, as the strongest impacts of climate warming are occurring in winter. Consequently, soils will experience more severe frost because warmer temperatures are not expected to counteract the reduced insulation. This has been shown to affect soil carbon and nutrient fluxes even into the following growing season. Vegetation responses, in particular root mortality, have been proposed as possible mechanisms, yet, this remains to be investigated.
In addition, it is unclear if already one extreme winter can induce changes in boreal vegetation, or if changes only occur after long-term alterations.
We use one of the longest ongoing snow removal experiments worldwide paired with a newly established treatment to directly compare short- (1 year) and long-term (11 years) effects of an absent snow cover and consequently severe soil frost (mean depth of almost 50 cm instead of less than 20) on above- and belowground parts of vegetation in a Norway Spruce forest in northern Sweden.
Results/Conclusions
In the forest understory, vascular plants in the long-term treatment had reduced shoot growth, their cover had decreased by 93% and root biomass had decreased by 40% compared to the control. At the same time, bare ground had increased and bryophyte cover slightly decreased. These effects were seen as trends in the short-term manipulation, yet were less substantial and thus not significant. However, the short-term manipulation resulted in severe visible frost damage of in average 30% on shoots of understory dwarf shrubs and delayed their spring phenology by over a week, compared to the control. Surprisingly, this was not present in the long-term manipulation, which could indicate either an adaptation of the vegetation to the long lasting severe frost, or a survival of only those individuals that can cope with these extreme conditions.
Thus, while the short-term manipulation affected some of the aboveground, possibly plastic, response parameters, the more significant and far-reaching ecosystem effects were only seen in the long-term experiment. In general, snow removal significantly affects boreal vegetation both above- and belowground with implications for soil carbon and nutrient cycling.