Model Category: Conceptual
Image: 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.
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.
Following disturbance such as prolonged cultivation and erosion, ecosystems start recovering along trajectories that will eventually lead to a stable state. Not all ecosystems, however, can reach the same pre-disturbance stable state (D'Odorico et al. 2001, Scheffer et al. 2001, Ridolfi et al. 2011, Runyan et al. 2012). In fact, when key ecosystem functions are lost, a new, degraded state may develop and persist, with reduced capacity to exchange and store water, carbon, and nutrients (see figure above). Thus we hypothesize that from a dynamical system point of view (e.g., Strogatz, 1994; Ridolfi et al. 2011), the negative effects of feedbacks and nonlinear interactions are responsible for the emergence of alternative attractors (exemplified by minima of potential wells in the figure). 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.
D'Odorico, P., A. Porporato, and L. Ridolfi. 2001. Transition between stable states in the dynamics of soil development. Geophysical Research Letters 28:595-598.
Ridolfi, L., P. D'Odorico, and F. Laio. 2011. Noise-Induced Phenomena in the Environmental Sciences. Cambridge University Press, Cambridge. 322 p.
Runyan, C. W., P. D'Odorico, and D. Lawrence. 2012. Physical and biological feedbacks of deforestation. Reviews of Geophysics 50.
Scheffer, M., S. Carpenter, J. A. Foley, C. Folke, and B. Walker. 2001. Catastrophic shifts in ecosystems. Nature 413:591-596.
Strogatz S. H., 1994, Nonlinear Dynamics and Chaos: With Applications To Physics, Biology, Chemistry, And Engineering, Westview Press.