Inter- and intra-annual variation in the pulsed flowering phenology of the columnar cactus Pilosocereus leucocephalus and its relation to temperature, rainfall and plant size

Abstract

Floral phenology involves the initiation and development of ecological and physiological processes (e.g. pollination, germination, etc.) that contribute to the successful recruitment of a plant species. However, aspects related to the inter and intra-annual variation of flowering patterns have been poorly studied, including pulsed flowering, which is a rare phenology in angiosperm plants with only three cases known in the family Cactaceae. Here, we analyzed the pulsed flowering phenology of the columnar cactus Pilosocereus leucocephalus between and within years and its relation to rainfall, environmental temperature, and plant size. We recorded the number of receptive flowers displayed by an initial population of 82 individual plants for five consecutive years in central Veracruz, Mexico. We calculated and compared 14 descriptors of the phenological pattern and found variation in flower production both within and between years; however, across years, the phenological pattern was consistently extended, pulsed, slightly synchronous, and with a low reproductive potential. Flower production was positively correlated with the maximum temperature of the fifteenth day before anthesis and poorly correlated with rainfall at the study site. The accumulated flower number over five years was positively related to cactus size. Overall, our results support the idea that the pulsed floral phenology of this cactus is a result of resource limitation that forces individuals to rest and restore the resources needed for flower production.