Abstract
The spatial pattern of vegetation patchiness may follow universal characteristic rules when the system is close to critical transitions between alternative states, which improves the anticipation of ecosystem-level state changes which are currently difficult to detect in real systems. However, the spatial patterning of vegetation patches in temperature-driven ecosystems have not been investigated yet. Here, using high-resolution imagery from 1972 to 2013 and a stochastic cellular automata model, we show that in a North American coastal ecosystem where woody plant encroachment has been happening, the size distribution of woody patches follows a power law when the system approaches a critical transition, which is sustained by the local positive feedbacks between vegetation and the surrounding microclimate. Therefore, the observed power law distribution of woody vegetation patchiness may be suggestive of critical transitions associated with temperature-driven woody plant encroachment in coastal and potentially other ecosystems.
Highlights
The spatial pattern of vegetation patchiness may follow universal characteristic rules when the system is close to critical transitions between alternative states, which improves the anticipation of ecosystem-level state changes which are currently difficult to detect in real systems
Previous work suggests that temporal dynamics of vegetation patterns may provide robust evidence of ecosystem regime shifts[28], recent modeling studies questioned the universality of indicators of critical transitions based on patch size distribution[29]
Our parametrized model shows the emergence of a critical transition as a result of this positive feedback[7], suggesting that the observed shift in plant cover is associated with a bifurcation in the underlying plant community dynamics
Summary
The spatial pattern of vegetation patchiness may follow universal characteristic rules when the system is close to critical transitions between alternative states, which improves the anticipation of ecosystem-level state changes which are currently difficult to detect in real systems. Woody canopies can absorb part of the nighttime long-wave radiation from the ground surface and reflect or reradiate it back to the ground, reducing radiative cooling and creating a warmer microclimate compared to adjacent open canopy areas and grasslands[16,18] Because of this positive feedback, a non-linear shift from one stable state with grass cover to another with woody plant dominance may occur in many cold-stressed ecotones worldwide when the minimum temperature increases above a critical threshold[8,16]. We investigate the spatiotemporal dynamics of woody plant encroachment and document how, as they approach the critical point, spatial patterns of vegetation exhibit power-law distributions of patch size
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