Oecologia (Berl.) 14, 295--306 (1974) 9 by Springer-Verlag 1974 Seasonal Carbon Allocation in Heteromeles arbutifolia, a California Evergreen Shrub H. A. Mooney and Celia Chu Department of Biological Sciences, Stanford University, Stanford, California 94305 Received November 2, 1973 Summary. The seasonal patterning of carbon gain and allocation was studied in the California evergreen sclerophyll shrub, Heteromeles arbuti/olia. Specifically an analysis was made of the seasonal structural allocations to stems, leaves, roots and reproductive parts as well as to functional categories of cell structure, metabolism, storage, and secondary compounds (predator protection). The differential partitioning during the various seasons is viewed in terms of the overall carbon economy of the shrub. It is suggested that not all functions can be met simultaneously, even though there is year round carbon gain, because of the heavy allocation demands to meet a particular environmental stress during a given season. For example, during the spring there is a priority allocation to the develop- ment of the canopy, apparently for competitive purposes, with little going to repro- duction, storage and secondary compounds. Introduction Plants allocate their carbon resources to diverse functions including growth, storage, maintenance, and protection. The timing, forms and amounts of these allocations represent the means by which plants meet the demands of their environment. Although these generalities are well established there are few studies which quantify these relationships (Mooney, 1972). Oechel et al. (1972) have described for a desert shrub, Larrea divari- cata, a fairly uniform partitioning of photosynthates within the plant through the entire year. Would this pattern also be true in plants in more light limited and competitive enviromments ? In order to investigate these relationships an evergreen sclerophyll shrub, Heteromeles arbuti- /oliaM. t~oem. (toyon), was chosen for study. This plant is a characteristic species of the California chaparral and is found throughout the geogra- phical extent of this vegetation type (Morrow, 1971). It is a rosaceous, deep-rooted shrub attaining average heights of two meters. In certain coastal areas however, this plant may attain tree-like proportions. Carbon Gain and the Environment The distribution of Heteromeles is centered in the mediterranean cli- mate regions of California. The summers are hot and dry and the winters 21 Oecologia (Berl.), VoI. 14