Increasing Vegetation on River Bars

Denali contains over 9,000 linear miles of rivers and streams, a distance that would stretch over halfway around the earth! Rivers are powerful agents of change, particularly glacier-fed rivers, which constantly transform the park landscape by transporting huge loads of sediment ground up by glacial movement high in the mountains.

Examining change over any time period, we would expect gravel bar vegetation growing on the edge of these glacial rivers and streams to erode in some areas and develop anew in other areas over time, leading to neither a net gain nor loss of gravel bar vegetation. However, upon close examination of these photo pairs, we noticed an apparent increase in vegetative cover of gravel bars across the park over a thirty-year period. What makes this observation significant is not any single photo pair, but that the trend was apparent in almost every single photo pair exhibiting gravel bars.

The very conspicuous change in the relative vegetation density on river bars over a short span of time was perhaps the most surprising and dramatic insight that we have gained from studying the repeated photos so far. What do you think might be behind this big shift in riparian vegetation? Even though the photos revealed an overall increase in vegetative colonization of gravel bars, as you browse the photo pairs, can you pick out locations where the river or stream has eroded vegetation away?