Present Effects of Past Wildfires on Leaf Litter Breakdown in Stream Ecosystems

Physicochemical and biological responses of streams to wildfire severity in riparian zones

“…CPOM concentrations, and shredder and predator densities, recovered within 2–4 years at sites in burned basins with intact riparian canopies, but CPOM and shredders remained at low levels where riparian vegetation burned, indicating the importance of riparian vegetation recovery for CPOM and shredder abundances (Koetsier et al ., ; Vieira et al ., ). CPOM levels appear to depend on fire‐induced leaf fall, inputs of charcoal and other burned material, the density, condition and recovery of riparian vegetation, the timing, intensity and frequency of scouring floods, the occurrence of landslides and stream geomorphological and flow characteristics (Britton, ; Gresswell, ; Robinson et al ., ; Koetsier et al ., ). Further complexities arise when examining fire effects on FPOM levels, which are affected not only by the factors influencing CPOM and algal levels, but also by factors, such as water temperature and shredder densities, which affect the breakdown of CPOM and generation of FPOM (Koetsier et al ., ; Vieira et al ., ; Verkaik et al ., ).…”

“…Subsequently, algal levels at BRB sites declined, despite high light levels, perhaps because nutrient concentrations had fallen or because grazer densities were high; consequently, there may be only brief periods of time when algal blooms are evident following riparian fires. Complexities in the effects of disturbance, light and nutrient levels on algal biomass and growth can account, perhaps, for some of the variable results observed in previous studies, ranging from negative to no to positive algal responses to fire (Bêche et al ., ; Koetsier et al ., ; Malison & Baxter, ; Oliver et al ., ; Verkaik et al ., ). In general, algal abundance after fires will depend on the intensity of scouring flood disturbances, post‐flood sediment deposition, turbidity, riparian canopy cover and nutrient concentrations, which vary with the time since fire and subsequent floods (Coombs & Melack, ; Verkaik et al ., ).…”

“…Although fires have been suggested to shift the base of stream food webs from allochthonous leaf litter inputs to autochthonous algal production, predominantly by reducing riparian canopy cover (Mihuc & Minshall, ), reported responses of stream algae, particulate organic matter, invertebrates and fish to fire have been inconsistent (Minshall, Royer & Robinson, ; Bêche, Stephens & Resh, ; Arkle & Pilliod, ; Malison & Baxter, ; Romme et al ., ; Oliver et al ., ; Verkaik et al ., ). These variable responses of stream communities to fire have been attributed to variation in the extent, severity and spatial pattern of fires, duration and intensity of subsequent run‐off events, occurrence of post‐fire landslides, size of stream and time since fire (Gresswell, ; Minshall et al ., ; Vieira et al ., ; Robinson, Uehlinger & Minshall, ; Arkle, Pilliod & Strickler, ; Koetsier, Krause & Tuckett, ; Malison & Baxter, ; Romme et al ., ; Sestrich, McMahon & Young, ).…”

“… Increased fire‐induced run‐off and erosion associated with winter rains will increase stream discharge, sediment transport and deposition and nutrient concentrations, as well as remove particulate organic matter and organisms (Shakesby, ; Warrick et al ., ; Coombs & Melack, ; Verkaik et al ., ). Stream reaches where riparian vegetation burned will have decreased canopy cover and leaf litter inputs, and increased water temperature and algal biomass, resulting in increased algivore and decreased detritivore densities (Koetsier et al ., ; Malison & Baxter, ; Vieira, Barnes & Mitchell, ; Verkaik et al ., ). By extirpating trout, which consistently reduce the abundance of invertebrate predators, wildfire will increase invertebrate predator densities (Wiseman, Cooper & Dudley, ; Meissner & Muotka, ); however, invertebrate predator effects on primary consumers will be counterbalanced by bottom‐up interactions stemming from wildfire effects on basal resources (algae, leaf litter). Food webs will be based on algal resources in streams where riparian vegetation burned but on detrital resources derived from riparian leaf litter in streams where riparian vegetation remained intact (Mihuc & Minshall, ). …”

Responses of riparian tetragnathid spiders to wildfire in forested ecosystems of the California Mediterranean climate region, USA

“…Changes in channel geometry following wildfire can be variable (Verkaik et al 2013a), but fire-induced changes in stream hydrogeomorphology (greater stream discharge, reduced sediment supply, and streambed incision; Legleiter et al 2003, May and Gresswell 2003, Shakesby 2011 can alter benthic macroinvertebrate larval populations with concomitant effects on adult emergence. In particular, loss of riparian leaf-litter inputs (Jackson et al 2012) and scouring flows (Koetsier et al 2010, Vieira et al 2011 can decrease shredder abundance and lead to shifts in the diet of individual taxa (Mihuc and Minshall 1995, Spencer et al 2003). In small headwater streams, higher densities of emergent insects have been associated with burned catchments (Mellon et al 2008).…”