An Assessment of Deadhead Logs and Large Woody Debris Using Side Scan Sonar and Field Surveys in Streams of Southwest Georgia

Abstract

Abstract Large woody debris provides essential habitat in sand-bed streams of the southeastern United States. In many Coastal Plain streams, pre-cut timber, lost more than a century ago during river transport, contributes to the extant large woody debris pool. The extraction of these logs, otherwise known as deadhead logging, threatens habitat integrity in these systems. Little is known of the distribution, abundance, and ecological value of deadhead logs, thus hindering attempts to manage and protect this resource. Moreover, the use of traditional field-based methods to inventory wood is slow and costly in large turbid streams. Our objectives were to assess wood at several sites in southwest Georgia using traditional methods, then use these data to evaluate the efficacy of quantifying wood using side scan sonar imagery. Deadhead logs were widely distributed and constituted a substantial proportion (> 50% volume and surface area) of the total large woody debris found at study sites. Given these findings, the wholesale removal of deadhead logs could largely impact the ecological integrity of such streams. Analyses revealed strong correlations (r2 = 0.82—0.98) between sonar wood estimates and actual counts suggesting that side scan sonar can be used as a rapid, inexpensive method to quantify wood throughout navigable systems.