The Population Dynamics of Columnar and Other Cacti: A Review

ABSTRACT

In this article, we review the population cycles of cacti, with an emphasis on the large, often keystone columnar cacti of the North American deserts. These and many other cacti often experience dramatic increases and declines in their numbers. Seeds that germinate in years that provide favourable conditions for regeneration and subsequently survive establish a cohort. We first review the limitations to estimating the age of any given individual; without this information, we cannot reconstruct the age of a population and reconstruct its age structure and demography. We then discuss the techniques for so doing, the data that are available, and the work that has been carried out on a few limited and isolated populations, primarily of Carnegiea gigantea. We then link century-scale population fluctuations with micro, local, regional and global climate factors, which include nurse-plant relationships, periodic freezing and El Niño events, and proceed to elaborate on the factors that influence cactus demographics, such as dispersal, pollination, human impacts and climate change.