Phenological patterns of nine perennial plants in an intertropical semi-arid Mexican scrub

We explore the relationships between environmental factors and vegetative and reproductive phenology in nine dominant perennial plant species in a semi-arid ecosystem in central Mexico. In spite of the highly seasonal environment at the study site, and a relatively long dry period, at least one species was always in some phase of growth or reproduction for the duration of the study (April 1996June 1998). Two patterns in leafing were observed. Some shrub species maintained their leaves during the entire year, whereas others lost their leaves during the dry season. The cacti Neobuxbaumia tetetzo andCephalocereus columna-trajani showed slow growth, however they produced areoles throughout the study. Echinocactus platyacanthus ceased areolar production during the driest period of the study. Throughout the both years, the dispersion of flowering and fruiting peaks among all the species studied were random. However, these species formed four distinct groups based on reproductive phenology and life form. (1) Shrubs with a general root system (01m depth), Mimosa luisana andCaesalpinia melanadenia , and the succulent nanophanerophyte with shallow roots, E. platyacanthus, flowered and fruited during the rainy season; (2) Phreatophytic shrubs, Prosopis laevigata and Cercidium praecox, and succulent mesophanerophytes with shallow roots, N. tetetzo and C. columna-trajani, flowered and fruited before the rainy season; (3) Castela tortuosa, a shrub with general root system, was the only species to flower and fruit all year long; (4) The semisucculent shrub with general root system, Ipomoea arborescens, flowered and fruited after the rainy season. These phenological patterns were correlated principally with soil moisture, maximum temperature, and to a lesser degree, relative humidity and photoperiod. Our results support the hypothesis that the coexistence of these species in arid zones is due to differences in resource utilization.