A dynamical system model of eco‐geomorphic response to landslide disturbance

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AbstractVegetated landscapes form through the interactions of ecologic and geomorphic processes. These interactions are generally slow and steady, but they are occasionally the subject of abrupt disturbance. In humid uplands, for example, landslides episodically disrupt forest growth and regolith development, suddenly mobilize soil, regolith and bedrock, and facilitate runoff‐driven erosion by abruptly removing canopy protection over a wide area. Here we model such an environment as a stochastically perturbed dynamical system whose simplified low dimensionality makes its eco‐geomorphic interactions easier to explore and understand. The model captures some of the spatial variability across a catchment by treating an ensemble of subcatchments: in each, aggregated biomass and regolith coevolve as a two‐dimensional dynamical system subject to episodic disturbance by slope failure. This coevolution gives rise to a notional stable equilibrium between regolith and biomass, but one that is not achieved in practice where landslide disturbance is significant. Instead, a catchment‐scale, ensemble‐average state arises in which higher storm frequency entails thinner regolith, less biomass, and weaker canopy protection against runoff erosion. The model makes the counter‐intuitive prediction that, as rainfall‐triggered landslides become more frequent, their contribution to the erosion of weathered bedrock will diminish as the role from storm runoff erosion rises. In some environments apparently dominated by landsliding, the model predicts that runoff erosion may be more important in the removal of regolith and fine sediment from hillslopes than mass wasting.