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Question: We know of no study that has linked volcanic eruptions occurring anywhere worldwide and the local population cycles of any species. The keystone saguaro cactus (Carnegiea gigantea) establishes in cohorts. We test whether there is a statistical relationship between Carnegiea gigantea establishment and volcanic eruptions.

Location: Northern Sonoran Desert, Arizona, USA.

Methods: We use both a region-wide dataset made up of 30 populations, and a dataset from a marginal site. We incorporate data for over 750 individuals over an area of more than 50 000 km(2). We created a 111-year time series of population peaks and troughs and correlated this over the 111-year record with the annual Weighted Historical Dust Veil Index (WHDVI). A t-test compared establishment patterns with the WHDVI.

Results: We found a significant relationship between volcanism and C. gigantea regeneration at both the marginal site, and in the region-wide dataset.

Conclusions: We suggest that while different populations are influenced by temporary global temperature ameliorations to different extents, our results show that populations do derive significant benefits from volcanic eruptions that promote their regeneration over large portions of their range, as is also exhibited locally at our marginal site, where populations are most susceptible to the inhospitable conditions that are witnessed at the edge of their range. This paper draws a link between the population fluctuations and regeneration of a species locally with geologic events from distant parts of the earth.