Phenology of the Drought-Deciduous Shrub Lotus scoparius: Climatic Controls and Adaptive Significance

In regions of mediterranean climate drought deciduousness has been considered an important adaptation for many species. This investigation focuses on the influences of a mediterranean climate on the phenology of a drought-deciduous shrub Lotus scoparius ssp. scoparius. Two research sites were chosen in the Santa Ynez mountains northwest of Santa Barbara, California for the field investigations. Phenological progressions of leaf production, leaf composition, shoot elongation, lateral branch production, and flowering in even-aged stands of Lotus scoparius were correlated with such factors as temperature, relative humidity, soil moisture, plant water relations, and photoperiod. These correlations were determined during a characteristic and uncharacteristic growing season for this mediterranean-climate region. Field correlations were the basis for the design of laboratory experiments in which the influences of photoperiod, temperature, water stress, and total daily photon flux on the phenological development of Lotus scoparius were studied. Climatic controls over Lotus scoparius phenology are complex with water relations and photoperiod having the greatest influence. Photoperiodic control over leaf abscission during water stress, and leaf production following dormancy, were two important phenological phenomena related to the unpredictably fluctuating mediterranean climate of southern California. The complex climatic control over phenology in Lotus scoparius constitutes an adaptation to the California mediterranean climate.