Conceptual Models
We hypothesize that from a dynamical system point of view (e.g., Strogatz, 1994; Ridolfi et al. 2011), negative effects of feedbacks and nonlinear interactions are responsible for the emergence of alternate attractors. From a physical point of view, such attractors are understood to be stable (or ‘steady-state’) compared to the typical timescales of plant and soil organic matter evolution. This ‘alternative steady-state’ hypothesis will be tested using observations from all field sites and a minimalist ecosystem-level model describing key dynamics of soil-plant-water interactions.
Schematic of land degradation effects on ecosystem trajectories and dynamic equilibria. Cultivation, through erosion and loss of hydraulic and biogeochemical function of the surface soil, is hypothesized to modify the dynamics of the system such that it may be locked into alternative ‘stable’ states characterized by low ecosystem productivity and reduced function. The figure highlights current time point, hypothesized undisturbed and altered equilibria, and the attractor of ecosystem dynamics.
Dynamic Persistence
Dynamic Persistence of Alternative States
Following disturbance, ecosystems start recovering along trajectories that will eventually lead to a stable state.
In CZs altered by land degradation and soil erosion, loss of surficial horizons, and reductions in infiltration, deep rooting, macroinvertebrates, and aggregation, impede redevelopment of forests and CZs with high productivity, standing biomass, and environmental services characteristic of forests never converted to cultivation agriculture.
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