The incidence and role of gullies after logging in a coastal redwood forest

a r t i c l e i n f o The distribution and morphological characteristics of channels were mapped in a redwood forest at Caspar Creek, California, USA, to evaluate the extent to which recent logging has influenced channel conditions in the area. In the North Fork Caspar Creek watershed, second-cycle logging of the early 1990s appears to have triggered increased coalescence of discontinuous gullies within clearcut tributary watersheds, and upstream channel limits in logged watersheds are now located significantly farther upslope than in control watersheds. The magnitudes of observed increases in peakflow after logging are consistent with the change in drainage density. Relations between channel morphological variables and indices of stream power are less well-defined in logged watersheds than in controls, suggesting that logging may have led to disruption of previously established channel forms. Correlations between suspended sediment yields and indices of gully erosion suggest that in-channel erosion associated with hydrologic change is an important source of post-logging sediment at Caspar Creek. Common sediment-control measures, such as use of riparian buffer strips and reduction of road surface erosion, would not be effective for reducing sediment input from this source. Gullying has been triggered by increased runoff and reduced vegetation cover in many areas and is of great concern to land managers (Valentin et al., 2005). Gullies contribute to loss of fertile soils, disrupt transportation networks, and depress water tables in floodplains; and they create persistent sources of sediments that reduce water quality, fill reservoirs, aggrade downstream channels, and impair aquatic habitats. Gullying can increase sediment yields both through incision of existing channels and by expansion of drainage networks into previously unchanneled swales. In the latter case, channel incision may increase transport capacity through the swale, providing hillslope-derived sediment more direct access to downstream channels (Reid, 1989). Most studies of gullies have been carried out in agricultural lands, grasslands, or arid areas, where the features are most visible and where they most directly challenge land-management activities; gullies in forests are less commonly encountered. Gullying occurred in some areas after conversion of forest to pasture or agriculture (e.g., Gábris et al., 2003; Parkner et al., 2006). In several areas, however, gullies have been identified as major sediment sources within unconverted forest lands. Often forest gullies are associated with road drainage or with areas compacted by logging equipment (e.g., Weaver et al., 1995; Croke and Mockler, 2001), but in other cases …