Soil seed banks, alternative stable state theory and ecosystem resilience

Abstract:

In many management contexts two alternative states exist: desired and degraded, sometimes separated by thresholds. Often the transition from desired to degraded state is based solely on the composition of the aboveground plant community. However, if the belowground propagules, such as the seed bank, still reflect the desired state then the system has inherent resilience and may not have crossed an irreversible threshold. We developed a conceptual framework integrating seed bank dynamics into alternative stable state theory, highlighting the important differences between aboveground and belowground composition. This integration highlights the role of resilience in systems that appear to have shifted to an “undesirable” state. A single system can exhibit both fast and slow dynamics simultaneously. That is, under chronic disturbance, such as grazing, aboveground vegetation may change faster than the soil seed bank because the seed bank represents an accumulation of historical vegetation while aboveground vegetation reflects the more immediate impacts of disturbance. Soil seed banks (and other forms of belowground propagules) provide buffering capacity and may serve as valuable indicators of potential resistance to state transition. In summary, ecosystem states may have multiple components that differ in their capacity to promote resilience. The application of alternative stable state theory from a management perspective should incorporate components of both above- and below-ground vegetation.