ABSENCE OF FLOWERING SHIFTS IN ARCTOSTAPHYLOS AND CEANOTHUS OVER THE PAST CENTURY OF CLIMATE WARMING

Abstract

Flowering phenology in five chaparral species was investigated using more than a century of data obtained from herbarium collections. Three species examined were from the genus Arctostaphylos (Ericaceae) and two from Ceanothus (Rhamnaceae). Collections of these species were examined relative to climate change data during the same time period. For all the species, no change in average flowering time occurred during the past century. Considerable variability was found in flowering phenology and this variability was explored using generalized linear (GLM) and generalized linear mixed models (GLMM) and different dimensions of temperature and precipitation timing. While the genera performed differently, both required combinations of precipitation, temperature, and their interactions to predict flowering date. Arctostaphylos responded the most to precipitation interactions, while Ceanothus responded the most to temperature interactions and the previous growing season's precipitation. In both genera, regression coefficients were combinations of both positive and negative variables, indicating that flowering dates are complex interactions among the different dimensions of precipitation and temperature.