Reactivation of supply-limited dune fields from blowouts: A conceptual framework for state characterization

Aeolian dune fields mantle the Earth in both vegetated (stable) and unvegetated (active) states. Changes in state are poorly understood; in particular, little is known about reactivation (devegetation) from a vegetated state. Available evidence indicates that dune reactivation can be driven by changes in aridity, increased wind speed, fire, biogenic disturbance, human disturbance, or a combination of the previous. How these controls fit together and define the reactivation potential of dune fields is presently unknown. Here we develop a framework to describe reactivation potential for a specific case: presently vegetated, supply-limited dune fields that develop blowouts under a unidirectional wind. We first define a conceptual model of blowout expansion, and then split the functions of vegetation in a stable dune field into: (i) maintenance of a protective skin, and (ii) blowout suppression. We model reactivation as disturbance breaking through the protective skin, which forms a blowout that is either (i) suppressed by colonizer species, or (ii) capable of advancing downwind and reactivating part of the dune field. The capacity for disturbance to break through the protective skin is a function of disturbance magnitude, area, and resistance of the skin. The blowout suppression capacity of a dune field is a function of sediment flux, blowout depth (related to geomorphology), and colonizer species vitality. By plotting a given dune field with two variables (protective skin breach rate and blowout suppression capacity) we define four states: (i) stable, (ii) blowout dominated, (iii) reactivating, or (iv) stable but disturbance susceptible. We reinforce the conceptual model with qualitative examples and discussion of experiments on grassland-stabilized dunes in Canada. Overall, our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields. (C) 2013 Elsevier B.V. All rights reserved.