The role of vegetation patch spatial configuration in landscape-scale flow-vegetation-sediment feedbacks

Abstract:

It is becoming increasingly recognized that processes affecting the planform configuration of marshes may be just as important as, if not more important than, vertical accretion and degradation processes. Sea-level rise may erode marshes laterally through wave action or expansion of the tidal channel network just as it may cause vertical inundation. Understanding the feedbacks contingent on the spatial configuration of vegetation patches and microtopography and their interactions with flow is critical to understanding the processes driving marsh persistence and predicting how marshes will respond to changes in environmental drivers. Based on case studies in the Florida Everglades and on generic modeled landscapes, we demonstrate approaches for quantifying spatial configuration and show how they may be used to distinguish between landscapes subject to different driving factors. These approaches include quantifying the connectivity of waterways using the directional connectivity index, quantifying characteristic patch length scales using autocorrelation functions, and state-space reconstruction based on cumulative width of vegetation patches in subsequent downstream cross-sections. Directional connectivity is particularly useful as an indicator of driving mechanisms governing the evolution of marsh landscapes, because connectivity engages directly in feedbacks with landscape-scale flow. We quantified the sensitivity of discharge through a modeled landscape subject to constant-head boundary conditions to different aspects of patch configuration, finding that directional connectivity and landscape fractal dimension were secondary only to patch area. Hence, changes in waterway connectivity caused by inundation (e.g., tidal marshes) or infilling (inland marshes) promote a positive feedback that amplifies the initial change and may contribute substantially to marsh degradation.