Nutrient availability and programmed senescence spatially structure the dynamics of an ecosystem engineer

Disentangling the extrinsic and intrinsic drivers on population dynamics is challenging due to the lack of relevant physiological and population information over appropriate space and time scales. Novel remote observations of giant kelp biomass and photosynthetic pigment concentrations are used to show that spatiotemporal patterns of physiological condition, and thus growth and production, are regulated by different processes depending on the scale of observation. Regional scale dynamics were linked to extrinsic nutrient supply and kelp forest stands in regions with elevated mean nutrient supply were more persistent over decadal timescales. However on local scales, intrinsic senescence processes, related to the age of canopy emergence, determined patterns of biomass loss across individual kelp forests, despite uniform nutrient conditions. Nascent technologies can quantify the roles of extrinsic and intrinsic factors at appropriate spatial and temporal scales to better understand plant population dynamics in global ecosystems.