Wolf‐triggered trophic cascades and stream channel dynamics in Olympic National Park: a comment on East et al. (2017)

Reply to ‘Wolf‐triggered trophic cascades and stream channel dynamics in Olympic National Park: a comment on East et al. (2017)’ by Robert Beschta and William Ripple

“…Despite Beschta and Ripple's suggestion, both our analysis and their independent analysis of our geographic information system (GIS) data show that the Hoh has widened (i.e. eroded its banks) relatively less than the Quinault and to a similar degree as the Queets River (Beschta & Ripple, 2017, figure 1). Moreover, we estimate that bedload could travel 30 km from the Hoh headwaters to our study reach in only 1-2 years, given that the Elwha River moved a massive bedload pulse 22 km from the former Lake Mills reservoir to the river mouth ( Figure 1A) in~1 year after a large dam removal, even with flows less than the two-year flood (Warrick et al, 2015) and in a channel with lower gradient than the upper Hoh watershed.…”

“…[Colour figure can be viewed at wileyonlinelibrary.com] 937 ESEX COMMENTARY boundary, consistent with an alternative explanation that forest harvesting and regeneration, as well as changes in elk, cougar, and black-bear hunting along the park boundary, likely have affected park elk populations since at least the 1980s (Jenkins et al, 2015). Beschta and Ripple (2017) also assert that our study would have greater utility if we had analyzed temporal change in the Clearwater and lower Quinault Rivers outside the park where elk density may be lower due to hunting. As our paper noted, the Clearwater and lower Quinault Rivers have important differences in physical setting, especially connection to upstream sediment delivery, that challenge any geomorphic comparisons with the Hoh, Queets, and upper Quinault Rivers (East et al, 2017).…”

“…Beschta and Ripple disagree with conclusions from our recent analysis of river planform change in Olympic National Park (East et al ., ). Beschta and Ripple (, ) believe that a trophic cascade consisting of wolf eradication, increase in elk abundance, and herbivory impacts on riparian vegetation has been the paramount driver of geomorphic change. Although the trophic‐cascade hypothesis is a valuable consideration for understanding riverine systems (Beschta and Ripple, ), we find that multiple physical processes have dominated river‐planform change in the glaciated, temperate‐rainforest valleys of Olympic National Park.…”

“…Beschta and Ripple () also assert that our study would have greater utility if we had analyzed temporal change in the Clearwater and lower Quinault Rivers outside the park where elk density may be lower due to hunting. As our paper noted, the Clearwater and lower Quinault Rivers have important differences in physical setting, especially connection to upstream sediment delivery, that challenge any geomorphic comparisons with the Hoh, Queets, and upper Quinault Rivers (East et al ., ).…”

“…Although Beschta and Ripple attribute excessive widening on the Quinault River to elk‐induced vegetation impairment, we attributed this unusual width to anthropogenic wood and riparian‐forest removal having affected the Quinault more than the other rivers (East et al ., ). Even ignoring temporary narrowing of the active channel in the 1970s (East et al ., , Figure 7), the unusually great cumulative terrace retreat on the Quinault (Beschta and Ripple, , figure ) is not attributable to excessive elk effects on vegetation, as Beschta and Ripple suggest, because the density of elk use is no greater on the Quinault than on the other rivers studied (Jenkins and Manly, ).…”