Catastrophic disturbances in headwater streams: the long-term ecological effects of debris flows and debris floods in the Klamath Mountains, northern California

Abstract

Debris flows and debris floods are catastrophic disturbances in steep, mountainous landscapes throughout the world, but little is known about the long-term ecological effects of these events on headwater streams. In 10 basins (10–20 km2) in the Klamath Mountains, northern California, USA, we used a space-for-time substitution to infer the long-term (10–100 years) effects of debris flows on stream ecosystem structure. Debris flows mobilized sediment and wood and removed riparian vegetation from large portions of channel networks. Stream temperatures were significantly warmer in streams that had recent debris flows (<10 years ago). Large wood, benthic organic matter, and detritivorous stoneflies were all very sparse in recent debris flow streams, suggesting that allochthonous energy pathways took decades to recover. Rainbow trout ( Oncorhynchus mykiss ) were abundant in recent debris flow streams, but populations of other vertebrates such as coastal giant salamander ( Dicamptodon tenebrosus ) and coastal tailed frog ( Ascaphus truei ) were virtually absent. Increased frequencies of catastrophic debris flows associated with forest management practices can have significant negative impacts on aquatic biodiversity in forested, mountainous landscapes.

Biological and water quality responses to hydrologic disturbances in third‐order forested streams

“…The prevalence of exposed bedrock in debris flow channels provides poor habitat for many aquatic invertebrates, and pools that do exist often lack cover, making them less than ideal for fish (Martin et al , 1986). Nonetheless, fish do colonize soon after the disturbance in available habitats (Lamberti et al , 1991; Roghair et al , 2002; Carline and McCullough, 2003; Cover et al , 2010). The limited work on lower trophic levels has consistently observed rapid colonization (Anderson, 1992; Snyder and Johnson, 2006) although major shifts in functional groups are evident (Anderson, 1992; Kobayashi et al , 2010).…”

The effects of severe flooding on native masu salmon and nonnative rainbow trout in the Atsuta River, Hokkaido, Japan

“…Some limitations of this study involved the luck of the control sites, including the reach-specific variability that was related to the timing of the investigation, and the habitat condition and the underestimation of the effects on environmental factors. In addition, the impacts from debris flow vary depending on the populations, species and environmental characteristics (Detenbeck et al 1992;Swanson et al 1998;Cover et al 2010;Danehy et al 2012). Further studies that are focused on these points should contribute substantially to our understanding of stream habitats and population persistence.…”

“…Debris flow may cause severe reductions in fish populations, alterations of water quality and long-term changes in habitat structure (Carline & McCullough 2003;Cover et al 2010;Danehy et al 2012). In addition, debris flow displaces stream substrates and large woody debris (LWD) that are important for the incubation and survival of eggs and fish as well as alters population age structures.…”

Natural and Anthropogenic Disturbance Influences on Aquatic Biological Diversity in the Pacific Northwest

“…Modern forest practices have been implemented to minimize current impacts and will provide the most benefit when mandated riparian buffers mature [10]. In larger streams where riparian forests were removed at first harvest, it will require centuries for a new forest to provide both adequate shading and large-wood loading [11,12]. Shading becomes effective sooner as streams decline in size, so stream conditions can recover more quickly in lower order systems.…”