Long-term monitoring data for perennial vegetation are difficult to obtain (Webb et al. 2009), particularly in remote terrain. Climate change and other anthropogenic influences have impacts on these isolated areas, and managers require scientific evaluations of landscape changes to make informed decisions about whether restoration or mitigation strategies are needed to ensure that resources remain intact for future generations. At the bottom of Grand Canyon (Arizona), the Colorado River winds about 450 km (280 miles) through a narrow, canyon-bound river corridor sustaining desert and riparian vegetation on substrates ranging from bedrock to river sandbars, creating a challenging environment for change-detection monitoring techniques (Belnap et al. 2008).
One method for evaluating change uses ground-based repeat photography to match historical images of landscapes (Webb et al. 2010). This technique, used worldwide to monitor environmental change, has a long history of application in Grand Canyon (Webb 1996). In the early 1990s, a unique set of images of the river corridor was used to document a variety of geomorphic and ecologic changes along the corridor of the Colorado River, including occurrence of debris flows that altered rapids, effects of feral burro grazing, longevity of desert shrubs, and notably influence of warming winter low temperatures on populations of frost-sensitive species (Webb and Bowers 1993; Bowers et al. 1995; Webb 1996). In 2010, 120 years after most of the original photographs were taken and about 20 years after the first series of matches, we revisited our camera stations in Grand Canyon National Park to further document changes in desert and riparian vegetation. Preliminary analysis of 151 new matches shows that original changes documented from 1990 to 1993 appear to be continuing, apparently showing the response of these ecosystems to climate change and river flow regulation.