Investigating the ecology of a threatened ecosystem: Alpine snowbank communities of Mt. Washington, NH

Abstract

In northeastern North America, alpine snowbank (or snowbed) communities are rare plant assemblages that form in sheltered sites above treeline where late-lying snow provides insulation from late-season frosts and a longer-lasting source of water. These communities are highly diverse and may provide many beneficial ecosystem services. Though work has been done to document their location and community composition, little is known about the relationships between plants and abiotic conditions in alpine snowbanks of the Northeast. We studied the relative effects of snowmelt date and temperature on the phenological responses of seven alpine snowbank plants and examined plant traits and community metrics (diversity and richness) across the snowmelt gradient at alpine snowbank sites on Mt. Washington, NH. Peak of observed phenophases was positively correlated with snowmelt date, but lag time (time between snowmelt date and peak phenophase) was negatively correlated with snowmelt date. Higher temperature was an important factor in the quickened phenological response of plants at later-melting sites. There was a clear transition in both community composition and traits across the snowmelt gradient; moving outward from snowbank cores, vascular plant diversity decreased and lichen diversity increased, with no trend evident in bryophytes. This corresponded to a transition in observed traits both within species and at the community-level, with snowbank core habitats having lower leaf dry matter content and greater height, leaf area, and specific leaf area than edge habitats. A similar difference in plant traits was observed among conspecifics between lowland and alpine habitats, though we were unable to conclude whether alpine ecotypes of those species exist. The change in environmental conditions across the snowmelt gradient, mediated by snow persistence, is important in determining plant phenological responses and growing conditions on Mt. Washington in ways as found elsewhere at similar sites worldwide. Due to prevalence of leafy species and reliance on specific environmental conditions, alpine snowbank communities are considered particularly sensitive to environmental change, and may be indicators of climatic trends occurring in northeastern North America.