Demographic shifts and plant succession along a late Holocene soil chronosequence in the Sonoran Desert of Baja California

Abstract

Three distinct alluvial terraces possess different vegetational assemblages. The oldest terrace is dominated by Larrea tridentata; higher densities of Idria columnaris and Pachycereus pringlei and greater species diversities characterise the two younger terraces. Demographic data indicate the vegetational differences are due to successional changes over time. On the oldest terrace, populations of Idria and Pachycereus exhibit higher per capita mortality and lower recruitment, indicating declines from what were originally denser populations. The rarity of Larrea on the younger terraces is attributed to exceedingly slow recruitment combined with the relatively short period of time that the youngest terraces have existed.