Fig 1.
Five stages of shrub expansion at which different shrub-permafrost interactions become “activated”, with the presence and relative magnitude of the effect outlined for each stage.
The bottom of the figure characterises the areal expansion of shrubs, which can occur independently of the vertical expansion of shrubs. Stages 1–4 represent the effects of purely vertical shrub expansion, while Stage 5 is caused by the areal expansion of tall shrubs to a degree that snow redistribution by wind is impeded. This framework can help us categorize the changing presence and magnitude of shrub-permafrost effects, and can help us explain the complex effects of shrubs on permafrost that we have observed. Figure designed by Lauren Thomas.