The Interface Between Snowfields and Treeline at Glacier National Park, Montana

Abstract:

Snowfields at Glacier National Park will likely retreat or disappear with climate change. GNP contains numerous snowfields previously designated as permanent, although this designation is no longer accurate. The edge of a snowfield moves inward while melting in summer and provides a water-rich microhabitat for alpine plants capable of growing in this harsh environment. We hypothesize that the species distribution of alpine plants will change with the retreat or disappearance of snowfields. Small, herbaceous plants live at the edges of snowfields, but trees and drought-tolerant, xeromorphic cushion plants may eventually inhabit the current snowfield edges.

We established permanent, geospatially referenced transects and plots in 2012-14 at the lateral and leading edges of snowfields at Siyeh, Logan, and Piegan Passes, at Preston Park, and the Mt. Clements moraine (the outer, downslope boundary of a vast snowfield). We used the Raunkiaer scheme to classify snowfield and proximal plants according to functional traits, the position of overwintering buds, and overall morphology. We characterized leaf morphology; developed height-frequency profiles; determined soil composition; and sieved soil to examine the seed bank.

The majority of the current snowfield edge plants are protohemicryptophytes, which means their buds overwinter at or just below the ground surface, or geophytes, which means their buds overwinter farther beneath the ground. Cushion plants were found farther from the snowfields while relatively thin-leaved (and likely less drought tolerant) plants were found near the snowfield’s edge.

Krummholz subalpine fir grows on the cliffs above the Mt. Clements snowfield, on the Mt. Clements moraine (15-20m from the snowfield) and 20-25m from the Piegan Pass snowfield. Krummholz whitebark pine grow within 50m of the snowfield at Piegan Pass. Non-krummnolz subalpine fir trees grow within 10m of the Preston Park snowfield’s upper edge. Trees were not found within 50m of the Siyeh Pass snowfield, which is characterized by harsh winds and a seemingly arid scree slope. It may be that the retreat and possible disappearance of the snowfields will open habitat that will eventually be colonized by trees, especially since these trees are currently found very close to most of the snowfields.