Effects of Fire on an Intermittent Stream: Monitoring the Response of the Aquatic Macroinvertebrate Community

Authors: Nathan Dorff, Michael Bogan

Year: 2016 (xlviii)

Abstract

Wildfires are natural disturbances that shape terrestrial landscapes and can alter aquatic ecosystems. Wildfires can be followed closely by flood events that cause debris flows and scouring, potentially compounding effects on aquatic systems. In 2011, the Horseshoe 2 Fire of southeast Arizona burned over 90,000 hectares and was followed by massive monsoonal rains. These rains triggered flood events that scoured creek beds within the range. In one stream within the affected area, East Turkey Creek, we monitored the aquatic macroinvertebrate community both pre- and postfire. Sampling began in 2008 and continues twice a year in three sites along the stream. We found that taxonomic richness was significantly reduced postfire, while overall abundance of aquatic macroinvertebrates remained the same. We also observed postfire increases in the relative abundances of certain r-strategist taxa. The most common taxa within the system prefire (baetid mayflies and blackflies) remained the most common following the fire, while other species were undetected for two years postfire, including the largest shredder and the top predator in the system. We have looked at three years of samples postfire and are continuing to monitor the macroinvertebrate response. Recovery to prefire levels of species richness took over two years, which is longer than what has been observed in similar studies. Potential explanations for the slower recovery are the severity of the fire and the flood events that followed and the fact that the en tire drainage was impacted (e.g. no flood refuges). With hotter and drier conditions in the Southwest expected due to climate change, more frequent and higher severity fires may also occur. Understanding how these new fire regimes will alter aquatic systems will therefore become more important as climate continues to change.