State-and-transition background (Optional)

BACKGROUND

State-and-transition models are an increasingly common conceptual method of organizing knowledge of successional dynamics in ecosystems. Unlike older successional theories they allow for multiple successional pathways, do not assume a single “climax” and do not assume that successional change is reversible. They assume that a given ecosystem might be capable of shifting among multiple stable states, when a specific “trigger” leads to a transition. The model seeks to identify the primary stable states, and key phases within those states, and the transitions among them. States and phases are defined by structural properties such as dominant plants and other biota or biodiversity, and functional properties/processes such as frequent fire return intervals or high soil aggregate stability. The properties of states and phases may be dynamic (e.g. plant cover & community composition) or inherent (e.g. climate, soil properties, landscape physiography), and may confer resistance (the ability to maintain the same set of structural/functional properties, i.e. not change) or resilience (the ability to experience change but return to the original set of structural/functional properties) to ecosystem change. Phases within states are different varieties of a state, and transitions from one phase to another tend to be fairly common, easily triggered, and often reversible. Phases may also be spatial variants of a state, dictated by inherent factors. There are particular phases which are at-risk to transition to degraded states, due to their structural or functional properties. Dynamics within a state, i.e. shifts from phase to phase, tend to be characterized by negative feedbacks which confer resilience. In contrast, transitions among stable states, may be abrupt, may exhibit threshold behaviors. Every transition has an underlying trigger, or combination of triggers, for example introduction of grazing. The trigger initiates a change in structural or functional properties of the ecosystem (e.g. loss of vegetative cover, and disruption of soil surface aggregates), which may engage new processes which bring about a transition to a new state. These transitions may be monitored with indicators.

If you would like more background on the current state-and-transition modeling framework we suggest reading:

Briske et al. 2008. Rangeland Ecology & Management 61:359–367.

Bestelmeyer et al. 2009. Rangeland Ecology & Management 62:1-15.