Response and resilience of rivers to historical resource use in the Greater Yellowstone Ecosystem : a repeat photography analysis

Abstract

Repeat photographs provide a glimpse of the past and thus tell a story of how man and nature have shaped the landscape. With the use of repeat photography based on on-the-ground oblique images, this study investigated how historical natural resource uses (e.g., logging, mining, ranching, and dam building) have affected headwater rivers of the Greater Yellowstone Ecosystem (GYE). These rivers included the Gallatin, Yellowstone, Wind, Gros Ventre, Snake, Madison, and Green Rivers along with several of their tributaries. Oblique photo pairs or series of photos were compared using three types of analyses: quantitative pixel comparisons, rank order statistics, and individual descriptions, in order to identify changes in riparian vegetation cover, sinuosity, bankfull, and flood plain area. Additionally, additional data from a stream reach of the upper Yellowstone River in Paradise Valley, Montana, allowed for aerial comparisons to quantify vegetation cover and sinuosity within photo frame wedges of corresponding oblique photos. The results of the comparisons revealed: (1) increased riparian vegetation where anthropogenic perturbations had ceased, indicating resilience and recovery; (2) decreased riparian vegetation and sinuosity where impacts intensified; and (3) little change in riparian vegetation where human natural resource use continued at a similar intensity. Application of this methodology to more photo points and other regions will provide a better understanding of the extent of previous threats and how river systems have responded or continue to counter ongoing anthropogenic impacts.