Riparian Final Vegclass. Olympic National Park NRCA Westside Rivers Riparian Vegetation Project (2016)

Beschta and Ripple (2012) assert that increased elk populations in the Olympic National Park due to extirpation of wolves in the 1920’s has led to a reduction in riparian vegetation. They hypothesize that a decrease in this vegetation has led to an increase in erosion and undercutting of large conifer trees along the river banks, causing woody debris in the river, which in turn impacts channel morphology. Using imagery dating from 1939 and a set of digitized channel margins for each year, we classified vegetation changes that have occurred along the Hoh, Queets, and Quinault Rivers. We focused on identifying large conifers near the river that could impact water flow and channel morphology if undercut and classified all other vegetation as "other". METHODS: Our classification of large conifer trees along the river margins was based on three rules: 1) Minimum Height: we selected only those trees whose height would indicate the tree was at least 50-cm in diameter at the time of the imagery (calculated from LIDAR). Maximum Crown-Width: we used an estimated maximum crown width of 26-m for conifers in the Olympic National Park (Van Pelt et al., 2006) as an indicator of potential root structure size that could be undermined. A 13-m radius buffer was applied to all tree locations that met our minimum height requirement. 2) Distance-to-River: in order to capture potential channel migration that could occur for a given year, we used a 20-m buffer from the channel margin based on Van Pelt's estimated range of 16-26-m per year. We created an ArcGIS ModelBuilder tool that identified the conifers that met our conditions and created polygon outputs that could be used to split the river margins into segments of "conifer" and "other". For those imagery years that occurred prior to the LIDAR dates, we performed a visual inspection of the results and manually classified any areas where large conifer had existed but were undercut by the river historically. For those imagery years that occurred after the LIDAR dates, we manually corrected any locations where large conifer have since been removed by river migration and were misidentified by the tool. REFERENCES: Beschta, R.L., and W.J. Ripple. 2012. The role of large predators in maintaining riparian plant communities and river morphology. Geomorphology 157-158:88-98. Van Pelt, R., T. C. O’Keefe, J. J. Latterell, R. J. Naiman. 2006. Riparian Forest Stand Development along the Queets River in Olympic National Park, Washington. Ecological Monographs 76(2):277-298.