Frost stress is a major limitation on the distribution of plant species. Frost stress can be avoided by herbaceous plants through the placement of their frost-sensitive tissues (buds) below protective layers such as litter or soil. Snow cover is also an important insulator in cold climates. However, the protection of depth may come at the cost of slower emergence and growth in the spring, because of the greater layer of soil to pass through for stem and leaf emergence. To explore this tradeoff, we conducted a snow removal experiment in a self-assembled old field plant community outside of London, Ontario, Canada, and examined the responses by species and perennating structure. The old field was dominated by goldenrod (Solidago canadensis), but also contained numerous asters (Symphyotrichum spp.) and thistles (Cirsium and Sonchusspp.). Over the winter of 2015/2016, twelve 2 x 2m plots were selected, and six were assigned to snow removal and six were left as ambient snow control plots. Snow was removed opportunistically to subject the plants to increased frost stress. During the following growing season, species percent cover was assessed, as was percent cover by functional trait (organ of perennation, life form, and reproductive origin).
The winter was relatively mild, and snow removal only decreased the minimum soil temperature experienced over winter by an average of 1.5 degrees Celsius. Accordingly, there were no significant snow removal effects on total plant cover. However, there was a significant decline in the cover of red clover (Trifolium pratense), a species with buds at the soil surface on a branched taproot (mean percent cover within the control plots was 20%, as compared to 5% in the snow removal plots). This result is consistent with the low frost tolerance of leguminous plants reported elsewhere in the literature, although it was not clear to what extent the reduction in cover may have resulted from tissue frost damage or by physical disruption caused by frost heave. Overall, this study contributes to a better understanding of frost tolerance and community dynamics, with the inclusion of belowground traits.