The effects of psammophilous plants on sand dune dynamics

Abstract

Mathematical models of sand dune dynamics have considered different types of sand dune cover. However, despite the important role of psammophilous plants (plants that flourish in moving-sand environments) in dune dynamics, the incorporation of their effects into mathematical models of sand dunes remains a challenging task. Here we propose a nonlinear physical model for the role of psammophilous plants in the stabilization and destabilization of sand dunes. There are two main mechanisms by which the wind affects these plants: (i) sand drift results in the burial and exposure of plants, a process that is known to result in an enhanced growth rate, and (ii) strong winds remove shoots and rhizomes and seed them in nearby locations, enhancing their growth rate. Our model describes the temporal evolution of the fractions of surface cover of regular vegetation, biogenic soil crust, and psammophilous plants. The latter reach their optimal growth under either (i) specific sand drift or (ii) specific wind power. The model exhibits complex bifurcation diagrams and dynamics, which explain observed phenomena, and it predicts new dune stabilization scenarios. Depending on the climatological conditions, it is possible to obtain one, two, or, predicted here for the first time, three stable dune states. Our model shows that the development of the different cover types depends on the precipitation rate and the wind power and that the psammophilous plants are not always the first to grow and stabilize the dunes.

Biocrust as one of multiple stable states in global drylands

“…Across the environmental (aridity or precipitation) gradient, ecosystems displayed bistable states (bare soil and biocrust), one stable mixed state (biocrust and vascular plants), bistable states (mixed state and vascular plants), and one stable state (vascular plants). A similar pattern has been reported previously in theoretical studies that involved biocrusts as a system state variable (16,23,24). The crossed fold bifurcation differs from the classic fold bifurcation, for which two detached branches of stable states are separated by one unstable transition state (Fig.…”

Stability and bistability in a one‐dimensional model of coastal foredune height

“…This finding is supported by a bimodal distribution of observed foredune elevations from the Virginia Barrier Islands, USA [ Durán and Moore , ]. Multiple stable states have been observed in the fixed versus active state of sand dunes [ Yizahq et al ., , ; Kinast et al ., ; Bel and Ashkenazy , ] as well as other ecogeomorphic systems [e.g., Fagherazzi et al ., ; Coco et al ., ; Heffernan , ; Marani et al ., ; Carr et al ., ].…”

Predictability of dune activity in real dune fields under unidirectional wind regimes

“…Second, q brink is fully empirical, avoiding the numerous poorly understood issues with moisture, ice, and snow (prevalent at many of our sites) [e.g., Barchyn and Hugenholtz , ]. Third, q brink avoids poorly evaluated and unreliable sand flux equations, and derivative simplified comparison schemes such as “drift potential” [ Bel and Ashkenazy , ; Barchyn et al ., ]. Fourth, q brink produces an estimate that is local, not from a wind record tens or hundreds of kilometers away, or low‐resolution weather reanalyses.…”

“…The first problem is a lack of congruency between aspatial [e.g., Lancaster, 1988;Yizhaq et al, 2009;Bel and Ashkenazy, 2014] and spatial models [e.g., Durán and Herrmann, 2006]. The resultant fundamental relations between climate forcing and dune vegetation cover are profoundly different.…”