Reciprocal biotic control on hydrology, nutrient gradients, and landform in the greater everglades

Restoration can be viewed as the process of reestablishing both exogenous drivers and internal feedbacks that maintain ecosystems in a desirable state. Correcting exogenous and abiotic drivers is clearly necessary, but may be insufficient to achieve desired outcomes in systems with self-organizing biotic feedbacks that substantially influence ecological stability and timing of responses. Evidence from a broad suite of systems demonstrates the prevalence of biotic control over key ecosystem attributes such as hydroperiod, nutrient gradients, and landform that are most commonly conceived of as exogenously controlled. While a general theory to predict conditions under which biotic controls exert such strong feedbacks is still nascent, it appears clear that the Greater Everglades/South Florida landscape has a high density of such effects. The authors focus on three examples of biotic control over abiotic processes: hydroperiod and discharge controls exerted by peat accretion in the ridge-slough landscape; phosphorus (P) gradients that emerge, at least in part, from interactions between accelerated peat accretion rates, vegetation structure and fauna; and reinforcing feedbacks among land elevation, aquatic respiration, and carbonate dissolution that produce local and landscape basin structure. The authors propose that the unifying theme of biogeomorphic landforms in South Florida is low extant topographic variability, which allows reciprocal biotic modification of local site conditions via mechanisms of peat accretion (including via effects of landscape P redistribution on primary production) or limestone dissolution. Coupling these local positive feedbacks, which drive patch expansion, with inhibitory or negative feedbacks on site suitability at distance, which serve to constrain patch expansion, provide the mechanistic basis for landscape pattern formation. The spatial attributes (range and isotropy) of the distal negative feedback, in particular, control pattern geometry; elucidating the mechanisms and properties of these distal feedbacks is critical to restoration planning. Copyright © 2011 Taylor & Francis Group, LLC.

Duke Scholars

Author James Brendan Heffernan Environmental Sciences and Policy