One Hundred Years of Vegetation Succession in the Easton Glacial Foreland, Mount Baker, Washington, USA

Abstract

This research describes stages of primary succession in the Easton glacial foreland on Mount Baker, Washington. The Easton foreland is an alpine landscape displaying the processes of primary succession from barren substrate to a developed forest within 1.95 kilometers and over a short geologic period of approximately one hundred years. Patterns of vegetation succession vary among forelands around the world. In the Easton foreland, vegetation development was measured by percent cover, richness, and species diversity. Environmental variables (distance from glacier (proxy for time), elevation, soil moisture, photosynthetic active radiation (PAR), slope, and aspect) were measured to determine factors influencing vegetation development during primary succession. The main finding from this study is that distance from the Easton glacier is the most significant variable influencing vegetation development, and that the relationship between vegetation cover and distance is non-linear. This indicates a rapid establishment initially after the glacier retreats and a gradual development from about 40-100 years. This suggests a chronosequence is sufficient for explaining vegetation development on a small temporal and spatial scale. Vegetation cover and richness increased through succession, with low values of vegetation richness compared to a neighboring foreland. Diversity remained consistent at a Shannon-Wiener Diversity index value of about 1. The other environmental variables played a smaller role in vegetation development. Only fifteen plant species were found with the most abundant species being: Lupinus polyphyllus, Luetkea pectinata, Tsuga mertensiana. Most notable was the early presence of Tsuga mertensiana saplings within 20 years of glacial retreat, suggesting a relationship to the more developed forest on the surrounding moraines that are likely providing a seed-bank for the valley. The findings of this study advance the small but growing field of Cascadian foreland studies and contributes valuable information to the discussion of alpine ecosystems responses under anthropogenic climate change.