Conceptual four stage mechanistic model of phenological changes in P. pyrenaicus growth, resource allocation and rhizome source-sink strength during the temperate northern hemisphere growing season (adapted from Jones et al. 2018). LAI = leaf area index. Note linkage of above and belowground growth processes with changes in source-sink strength and that rhizome tissue sink strength increases through the winter from November, reaching a peak in April-June during senescence.