Multiscale, Hierarchical Models of Pulse Dynamics in Arid Ecosystems

Ecological processes in arid landscapes are generally described using a pulse-dynamic framework due to the dependence of most of these processes on brief pulses of water in an otherwise water-limited system.  Species and ecosystems respond to these pulse rain events, which have consequences at multiple spatial and temporal scales.  Integrating across these scales is of increasing research interest, particularly due to the looming issue of climate change, which is predicted to affect both the frequency, timing, and duration of rain events in arid systems, which would thus affect their ecological processes at multiple scales.  These processes include physiology of individuals, population growth rates, species interactions, as well as the flux of nutrients and energy within and through the ecosystem at a larger landscape scale (see figure).  The authors of this review describe these processes and how they can be integrated across spatial and temporal scales using a hierarchical pulse-dynamics framework.  They describe this framework based on 1.) exchanges between carbon or nutrient pools, such as through the activity of microbes decomposing litter in soil, or in the stimulation of primary production 2.) interactions between species, which affect population and community dynamics 3.) transitions of patches or ecosystems to different states, such as from grasslands to woody shrub-dominated communities, and 4.) transfers of materials across landscapes, such as soil erosion and nutrient loss during large-scale run-off events caused by extreme rain events.  These processes influence each other from the bottom up, (1 influencing 2, 2 influencing 3, etc), but can also feedback so that higher levels influence ones lower down in the hierarchy, which is organized by the temporal and spatial grain of the processes occurring at each level, moving from smaller to larger.  Although this framework is primarily conceptual, its hierarchical design makes it expandable into a more explicit multiscale model in the future.

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Collins, S. L. et al. (2014) A Multiscale, Hierarchical Model of Pulse Dynamics in Arid-Land Ecosystems. Annu. Rev. Ecol. Evol. Syst. 45, 397–419.