PHENOLOGY OF TETRAPLOID CREOSOTEBUSH, LARREA TRIDENTATA (DC.) COV., AT THE NORTHEASTERN EDGE OF THE SONORAN DESERT.

摘要

Phenology of tetraploid Larrea tridentata was studied at four sites, one east and three west of Tucson, Pima County, Arizona in 1972-1974 and 1981. Leaf initiation, stem elongation, flower buds, flowers, maturing fruits and mature fruits were recorded at regular intervals on a sample of 10 tagged plants at each site. Quantitative production of maturing fruits on each sampled plant was estimated during the 1981 spring and summer seasons. The time required for individual new flowers to develop into mature fruits was determined for 1981. These phenological data were related to precipitation and temperature during 1972-1974 and 1981.; Leaf initiation and stem elongation were continuously active on at least some parts of all sampled plants throughout the study, indicating year-round vegetative growth of Larrea in this part of the Sonoran Desert.; One or more of the four reproductive phenophases were present throughout the 1972-1974 and 1981 periods. Flower buds were initiated during any time of the year. Spring flowering was the most dependable, summer flowering was frequent but less consistent and fall and winter flowerings were occasional, irregular and far more variable. Spring flowering persisted longer than summer flowering. Maturing fruit production was much greater in the spring than in the summer. Approximately 53 to 65 days were required in the spring and 42 to 47 days in the summer for new flowers to develop into mature fruits.; Active vegetative growth invariably preceded the renewal of any reproductive activity. The emergence of flower buds appears to be triggered and sustained by the availability of sufficient soil moisture with minimal influence by temperature. However, higher temperatures tend to speed up the development of flower buds and flowers and fruit maturation. Differences in phenological responses among the four study sites appear to be caused mainly by local fluctuations in precipitation.; The year-round vegetative growth activity and the frequent recurrence of reproductive activities observed in this study represent adaptive responses of Larrea to the biseasonal regime and the moderate winter temperatures characteristic of the northeastern portion of the Sonoran Desert.