Wood Debris Recruitment and Movement Across Differing Riparian Landforms in a Coastal Plain Stream

Research Team: Dr. Stephen W. Golladay (Associate Scientist), Juliann M. Battle (Research Technician III), Dr. Brian Palik, and Charles Goebel

Wood debris is an important component of most streams and in the Coastal Plain is often the most productive habitat. Little is known about the long term dynamics of wood debris. Large floods also control key processes in stream and one of the ways floods affect streams is through the recruitment of coarse woody debris from stream-side forests. Stream valley geomorphology may mediate this interaction by altering flood velocity, depth, and duration. Little research has examined how floods and geomorphic features interact to control debris recruitment from riparian forests. With this in mind, we examined debris recruitment resulting from tree mortality during 2 floods in a southeastern Coastal Plain stream. We quantified debris characteristics as related to riparian geomorphology, and we examined the influence of floods on the structure of stream-side forests. In 1994, a record flood killed an average 22 trees/km, and a less severe flood in 1998 resulted in a loss of 11 trees/km. In 1994 the majority of tree mortality occurred on sand ridges and terraces in the lower reaches of the stream (70%). In 1998 mortality was still high on the sand ridges and terraces (> 45%), but trees were also recruited from the floodplains on the middle and upper reaches. Fifty-eight snags from the 1994 flood were not locatable after the 1998 flood. The majority were removed from the lower reaches, where snag density was the highest. Multivariate analysis revealed that snags in 1994 were oriented parallel to the bank and snags in ‘98 were frequently perpendicular. In 1994 snags tended to be closer to the stream and often lacked structural roots. The winter of 1998 was wetter than average because of El Nino. We hypothesize that trees on the upper and middle reaches were more susceptible to recruitment during the 1998 flood because saturated soils reduced the stability of individual trees. Variation in recruitment is influenced by stream valley geomorphology; mortality tends to be highest in areas having narrow valleys and high elevations of riparian landforms, while it was lowest in reaches having wide valleys and low landform elevations. Our results suggest that constrained reaches are the primary sources of debris during large floods, while unconstrained reaches function as debris sinks. Ongoing studies are examining the fate and movement of wood debris.

Additional Information:

Michener, W.K., E.R. Blood, J.B. Box, C.A. Couch, S.W. Golladay, D.J. Hippe, L.K. Kirkman, R.J. Mitchell, and B.J. Palik. 1998. Tropical storm flooding of a Coastal Plain landscape. BioScience 48: 696-705.

Palik, B.J., S.W. Golladay, P. Charles Goebel, and Brad W. Taylor. 1998. Influence of riparian geomorphology on coarse woody debris recruitment in a Georgia Coastal Plain stream. Ecoscience 5: 551-560.

Golladay, S.W., B.J. Palik, P.C. Goebel, and B.W. Taylor. 1997. Influence of riparian landform on large woody debris input and movement in a blackwater Coastal Plain stream. pages 197-200 in Proceedings of the 1997 Georgia Water Resources Conference. Kathryn J. Hatcher (ed.). Institute of Ecology, The University of Georgia, Athens. PDF version

Funded by: The Joseph W. Jones Ecological Research Center