The importance of secondary growth to plant responses to snow in the arctic

Abstract

In arctic environments, drifting snow around large shrub patches during winter may enhance growth by insulating the soil and facilitating overwinter nutrient turnover, leading to increased summer plant growth and potentially widespread increases in shrub cover. To determine whether snow enhances growth of arctic plants, we examined the effect of 6 years of added snow on plant biomass allocation and growth of nine common vascular plant species collected in 2010 and 2011 on either side of snowfences established in 2005 across a gradient of shrub biomass and productivity near Toolik Lake, Alaska. The deciduous shrub Salix pulchra responded most positively to added snow showing an 88% increase in total ramet biomass, because increased secondary growth allowed plants to support more branches and leaves. Some graminoid species also showed growth increases, especially where they were more abundant and larger than nearby shrub species. Species sharing the same growth strategy (deciduous shrubs, evergreen shrubs and graminoids) responded differently to increased snow, with some showing increased growth, others showing decreased growth, and some showing no effects. We found that relative biomass per ramet in combination with growth strategy is a better predictor of species’ growth responses to added snow than growth strategy alone. Our research shows that a primary mechanism for enhanced growth of shrubs in response to deeper snow is increased secondary growth. Improved growth may be an important way in which arctic plants spread, since they are often long-lived and clonal, and this may help explain the increase in shrub cover observed across northern latitudes. As shrub patches continue to expand and increase surrounding snow depths during winter, secondary growth of fast-growing deciduous shrub species may play an important role in defining future landscape community composition and ecosystem processes. A plain language summary is available for this article.