This research investigated how the strength of vegetation–soil–topography couplings varied along a gradient of biogeomorphic succession in two distinct fluvial systems: a forested river floodplain and a coastal salt marsh creek. The strength of couplings was quantified as tri-variance, which was calculated by correlating three singular axes, one each extracted using three-block partial least squares from vegetation, soil, and topography data blocks. Within each system, tri-variance was examined at low-, mid-, and high-elevation sites, which represented early-, intermediate-, and late-successional phases, respectively, and corresponded to differences in ongoing disturbance frequency and intensity. Both systems exhibited clearly increasing tri-variance from the early- to late-successional stages. The lowest-lying sites underwent frequent and intense hydrogeomorphic forcings that dynamically reworked soil substrates, restructured surface landforms, and controlled the colonization of plant species. Such conditions led vegetation, soil, and topography to show discrete, stochastic, and individualistic behaviors over space and time, resulting in a loose coupling among the three ecosystem components. In the highest-elevation sites, in contrast, disturbances that might disrupt the existing biotic–abiotic relationships were less common. Hence, ecological succession, soil-forming processes, and landform evolution occurred in tight conjunction with one another over a prolonged period, thereby strengthening couplings among them; namely, the three behaved in unity over space and time. We propose that the recurrence interval of physical disturbance is important to—and potentially serves as an indicator of—the intensity and mechanisms of vegetation–soil–topography feedbacks in fluvial biogeomorphic systems.

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Published in PLOS ONE, v. 11, no. 9, e0163223, p. 1-18.

© 2016 Kim, Kupfer.

This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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This research was supported by the National Science Foundation (BCS-0825753) and the U.S. Department of the Interior National Park Service.

Related Content

All data files are available in one of the Supporting Information files: S1 File.

journal.pone.0163223.s001.PDF (325 kB)
S1 Fig. Congaree River floodplain area.

journal.pone.0163223.s002.PDF (238 kB)
S2 Fig. Salt marsh creek area.

journal.pone.0163223.s003.XLS (375 kB)
S1 File. Procedure for 3B-PLS.

journal.pone.0163223.s004.TXT (1 kB)
S2 File. Procedure for estimating extra sums of squres.

journal.pone.0163223.s005.PDF (231 kB)
S1 Table. Average values of surface elevation, inundation depth, soil properties, and selected plant species abundance (18 most common only; basal area, cm2 ha–1) at each study site in the Bates Fork tract of Congaree National Park, South Carolina, USA.

journal.pone.0163223.s006.PDF (166 kB)
S2 Table. Average values of surface elevation, distance to the creek, soil properties, and all plant species abundance (% frequency) at each study site of the Skallingen salt marsh, Denmark.

journal.pone.0163223.s007.PDF (166 kB)
S1 Text. Study areas and data collection.

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