Fate of cohorts in Melocactus (Cactaceae) species is affected by rainfall uncertainty and microrelief structures

Abstract

Associations between plants and substrate in drylands enhance the ability of nutrient pools buildup and seedling establishment. However, this relationship has not been extensively demonstrated in populations of lithophytic plants. We report the effects of microrelief and neighboring plants on the population structure of Melocactus species in the semi-arid region of northeastern Brazil. The size classes of five populations and the seedling fate in two populations were examined through point pattern analysis. Association patterns between size classes were positive between seedlings and adults in all the populations. Cohorts were positively related to rainfall (>60 %). Recruitment events were microhabitat-dependent and showed high mortality levels (>70 %). The spatio-temporal decoupling between seedling fate and adults may favor population dynamic changes under rainfall uncertainty. Based on our analyses, we suggest that the relationship among size classes, microhabitat, and rainfall in lithophytic populations of Melocactus is crucial to buffer negative effects of environmental severity in seedling recruitment and survival.